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NAME

       xref  -  A  Cross  Reference  Tool  for analyzing dependencies between functions, modules,
       applications and releases.

DESCRIPTION

       Xref is a cross  reference  tool  that  can  be  used  for  finding  dependencies  between
       functions, modules, applications and releases.

       Calls  between  functions  are  either local calls like f(), or external calls like m:f().
       Module data, which are extracted  from  BEAM  files,  include  local  functions,  exported
       functions,  local calls and external calls. By default, calls to built-in functions () are
       ignored, but if the option builtins, accepted by some of this module's functions,  is  set
       to  true, calls to BIFs are included as well. It is the analyzing OTP version that decides
       what functions are BIFs. Functional objects are  assumed  to  be  called  where  they  are
       created  (and  nowhere  else).  Unresolved calls are calls to apply or spawn with variable
       module, variable function, or variable arguments. Examples are M:F(a), apply(M,  f,  [a]),
       and  spawn(m, f(), Args). Unresolved calls are represented by calls where variable modules
       have been replaced with the atom '$M_EXPR', variable functions have been replaced with the
       atom  '$F_EXPR',  and  variable number of arguments have been replaced with the number -1.
       The  above  mentioned  examples  are  represented  by  calls   to   '$M_EXPR':'$F_EXPR'/1,
       '$M_EXPR':f/1,  and  m:'$F_EXPR'/-1.  The  unresolved  calls  are a subset of the external
       calls.

   Warning:
       Unresolved calls make module data incomplete, which implies that the results  of  analyses
       may be invalid.

       Applications  are  collections of modules. The modules' BEAM files are located in the ebin
       subdirectory  of  the  application  directory.  The  name  of  the  application  directory
       determines  the  name  and  version  of  the  application.  Releases  are  collections  of
       applications located in the lib subdirectory of the release directory. There  is  more  to
       read about applications and releases in the Design Principles book.

       Xref servers are identified by names, supplied when creating new servers. Each Xref server
       holds a set of releases, a set of applications, and a set of  modules  with  module  data.
       Xref  servers are independent of each other, and all analyses are evaluated in the context
       of one single Xref server (exceptions are the functions m/1  and  d/1  which  do  not  use
       servers at all). The mode of an Xref server determines what module data are extracted from
       BEAM files as modules are added to the server. Starting with R7, BEAM files compiled  with
       the  option  debug_info  contain  so  called  debug  information,  which  is  an  abstract
       representation of the code. In functions mode, which is the default mode,  function  calls
       and  line numbers are extracted from debug information. In modules mode, debug information
       is ignored if present, but dependencies between modules are extracted from other parts  of
       the  BEAM  files. The modules mode is significantly less time and space consuming than the
       functions mode, but the analyses that can be done are limited.

       An analyzed module is a module that has been added to an Xref  server  together  with  its
       module  data.  A  library  module  is  a module located in some directory mentioned in the
       library path. A library module is said to be used if some of its  exported  functions  are
       used  by  some  analyzed module. An unknown module is a module that is neither an analyzed
       module nor a library module, but whose  exported  functions  are  used  by  some  analyzed
       module.  An  unknown  function is a used function that is neither local or exported by any
       analyzed module nor exported by any library module. An undefined function is an externally
       used  function  that  is  not exported by any analyzed module or library module. With this
       notion, a local function can be an undefined function, namely if  it  is  externally  used
       from some module. All unknown functions are also undefined functions; there is a figure in
       the User's Guide that illustrates this relationship.

       Starting with R9C, the module attribute tag deprecated can be used to  inform  Xref  about
       deprecated  functions  and  optionally  when  functions  are  planned to be removed. A few
       examples show the idea:

         -deprecated({f,1}).:
           The exported function f/1 is deprecated. Nothing is said whether f/1 will  be  removed
           or not.

         -deprecated({f,'_'}).:
           All exported functions f/0, f/1 and so on are deprecated.

         -deprecated(module).:
           All    exported    functions   in   the   module   are   deprecated.   Equivalent   to
           -deprecated({'_','_'})..

         -deprecated([{g,1,next_version}]).:
           The function g/1 is deprecated and will be removed in next version.

         -deprecated([{g,2,next_major_release}]).:
           The function g/2 is deprecated and will be removed in next major release.

         -deprecated([{g,3,eventually}]).:
           The function g/3 is deprecated and will eventually be removed.

         -deprecated({'_','_',eventually}).:
           All exported functions in the module are deprecated and will eventually be removed.

       Before any analysis can take place, module data must be set up. For  instance,  the  cross
       reference  and  the  unknown  functions  are  computed when all module data are known. The
       functions that need complete data (analyze, q, variables) take care  of  setting  up  data
       automatically.  Module  data  need  to  be  set  up (again) after calls to any of the add,
       replace, remove, set_library_path or update functions.

       The result of setting up module data is the Call Graph. A (directed) graph consists  of  a
       set  of  vertices  and  a  set  of  (directed) edges. The edges represent calls (From, To)
       between functions, modules, applications or releases. From is said to call To, and  To  is
       said  to  be  used by From. The vertices of the Call Graph are the functions of all module
       data: local and exported functions of analyzed modules; used BIFs; used exported functions
       of  library  modules;  and  unknown  functions. The functions module_info/0,1 added by the
       compiler are included among the exported functions, but only when called from some module.
       The  edges  are  the function calls of all module data. A consequence of the edges being a
       set is that there is only one edge if a function is locally  or  externally  used  several
       times on one and the same line of code.

       The  Call Graph is represented by Erlang terms (the sets are lists), which is suitable for
       many analyses. But for analyses that look at chains of calls,  a  list  representation  is
       much  too  slow.  Instead  the  representation  offered by the digraph module is used. The
       translation of the list representation of the Call Graph - or a subgraph thereof - to  the
       digraph representation does not come for free, so the language used for expressing queries
       to be described below has a special operator for this task and a possibility to  save  the
       digraph representation for subsequent analyses.

       In  addition  to  the  Call  Graph there is a graph called the Inter Call Graph. This is a
       graph of calls (From, To) such that there is a chain of calls from From to To in the  Call
       Graph,  and  every  From  and  To is an exported function or an unused local function. The
       vertices are the same as for the Call Graph.

       Calls between modules, applications and releases are also directed graphs.  The  types  of
       the  vertices  and  edges  of  these graphs are (ranging from the most special to the most
       general): Fun for functions; Mod for modules; App for applications; and Rel for  releases.
       The  following  paragraphs will describe the different constructs of the language used for
       selecting and analyzing parts of the graphs, beginning with the constants:

         * Expression ::= Constants

         * Constants ::= Consts | Consts : Type | RegExpr

         * Consts ::= Constant | [Constant, ...] | {Constant, ...}

         * Constant ::= Call | Const

         * Call ::= FunSpec -> FunSpec | {MFA,  MFA}  |  AtomConst  ->  AtomConst  |  {AtomConst,
           AtomConst}

         * Const ::= AtomConst | FunSpec | MFA

         * AtomConst ::= Application | Module | Release

         * FunSpec ::= Module : Function / Arity

         * MFA ::= {Module, Function, Arity}

         * RegExpr ::= RegString : Type | RegFunc | RegFunc : Type

         * RegFunc ::= RegModule : RegFunction / RegArity

         * RegModule ::= RegAtom

         * RegFunction ::= RegAtom

         * RegArity ::= RegString | Number | _ | -1

         * RegAtom ::= RegString | Atom | _

         * RegString  ::=  -  a  regular  expression,  as described in the re module, enclosed in
           double quotes -

         * Type ::= Fun | Mod | App | Rel

         * Function ::= Atom

         * Application ::= Atom

         * Module ::= Atom

         * Release ::= Atom

         * Arity ::= Number | -1

         * Atom ::= - same as Erlang atoms -

         * Number ::= - same as non-negative Erlang integers -

       Examples of constants are: kernel, kernel->stdlib, [kernel, sasl],  [pg  ->  mnesia,  {tv,
       mnesia}]  :  Mod.  It is an error if an instance of Const does not match any vertex of any
       graph. If there are more than one vertex matching an untyped instance of  AtomConst,  then
       the one of the most general type is chosen. A list of constants is interpreted as a set of
       constants, all of the same type. A tuple of constants constitute a chain of  calls  (which
       may,  but  does  not  have  to,  correspond  to  an  actual chain of calls of some graph).
       Assigning a type to a list or tuple of Constant is equivalent to  assigning  the  type  to
       each Constant.

       Regular  expressions  are  used  as  a  means to select some of the vertices of a graph. A
       RegExpr consisting of a RegString and a type  -  an  example  is  "xref_.*"  :  Mod  -  is
       interpreted  as  those  modules  (or applications or releases, depending on the type) that
       match the expression. Similarly, a RegFunc is interpreted as those vertices  of  the  Call
       Graph  that  match the expression. An example is "xref_.*":"add_.*"/"(2|3)", which matches
       all add functions of arity two or three of any of the xref modules. Another  example,  one
       that  matches  all functions of arity 10 or more: _:_/"[1-9].+". Here _ is an abbreviation
       for ".*", that is, the regular expression that matches anything.

       The syntax of variables is simple:

         * Expression ::= Variable

         * Variable ::= - same as Erlang variables -

       There are two kinds of variables: predefined  variables  and  user  variables.  Predefined
       variables  hold  set  up  module data, and cannot be assigned to but only used in queries.
       User variables on the other hand can be assigned to, and are typically used for  temporary
       results while evaluating a query, and for keeping results of queries for use in subsequent
       queries. The predefined  variables  are  (variables  marked  with  (*)  are  available  in
       functions mode only):

         E:
           Call Graph Edges (*).

         V:
           Call Graph Vertices (*).

         M:
           Modules. All modules: analyzed modules, used library modules, and unknown modules.

         A:
           Applications.

         R:
           Releases.

         ME:
           Module Edges. All module calls.

         AE:
           Application Edges. All application calls.

         RE:
           Release Edges. All release calls.

         L:
           Local Functions (*). All local functions of analyzed modules.

         X:
           Exported  Functions.  All exported functions of analyzed modules and all used exported
           functions of library modules.

         F:
           Functions (*).

         B:
           Used BIFs. B is empty if builtins is false for all analyzed modules.

         U:
           Unknown Functions.

         UU:
           Unused Functions (*). All local and exported functions of analyzed modules  that  have
           not been used.

         XU:
           Externally Used Functions. Functions of all modules - including local functions - that
           have been used in some external call.

         LU:
           Locally Used Functions (*). Functions of all modules that have been used in some local
           call.

         LC:
           Local Calls (*).

         XC:
           External Calls (*).

         AM:
           Analyzed Modules.

         UM:
           Unknown Modules.

         LM:
           Used Library Modules.

         UC:
           Unresolved Calls. Empty in modules mode.

         EE:
           Inter Call Graph Edges (*).

         DF:
           Deprecated Functions. All deprecated exported functions and all used deprecated BIFs.

         DF_1:
           Deprecated Functions. All deprecated functions to be removed in next version.

         DF_2:
           Deprecated  Functions.  All deprecated functions to be removed in next version or next
           major release.

         DF_3:
           Deprecated Functions. All deprecated functions to be removed  in  next  version,  next
           major release, or later.

       These  are  a  few facts about the predefined variables (the set operators + (union) and -
       (difference) as well as the cast operator (Type) are described below):

         * F is equal to L + X.

         * V is equal to X + L + B + U, where X, L, B and U are pairwise disjoint (that is,  have
           no elements in common).

         * UU  is  equal  to  V  - (XU + LU), where LU and XU may have elements in common. Put in
           another way:

         * V is equal to UU + XU + LU.

         * E is equal to LC + XC. Note that LC and XC may have elements in common, namely if some
           function is locally and externally used from one and the same function.

         * U is a subset of XU.

         * B is a subset of XU.

         * LU is equal to range LC.

         * XU is equal to range XC.

         * LU is a subset of F.

         * UU is a subset of F.

         * range UC is a subset of U.

         * M is equal to AM + LM + UM, where AM, LM and UM are pairwise disjoint.

         * ME is equal to (Mod) E.

         * AE is equal to (App) E.

         * RE is equal to (Rel) E.

         * (Mod)  V  is  a  subset  of M. Equality holds if all analyzed modules have some local,
           exported, or unknown function.

         * (App) M is a subset of A. Equality holds if all applications have some module.

         * (Rel) A is a subset of R. Equality holds if all releases have some application.

         * DF_1 is a subset of DF_2.

         * DF_2 is a subset of DF_3.

         * DF_3 is a subset of DF.

         * DF is a subset of X + B.

       An important notion is that of conversion of expressions. The syntax of a cast  expression
       is:

         * Expression ::= ( Type ) Expression

       The  interpretation  of  the  cast  operator  depends  on the named type Type, the type of
       Expression, and the structure of the elements of the interpretation of Expression. If  the
       named  type  is  equal  to  the  expression  type,  no  conversion is done. Otherwise, the
       conversion is done one step at a time; (Fun) (App) RE,  for  instance,  is  equivalent  to
       (Fun)  (Mod)  (App)  RE.  Now  assume  that  the  interpretation of Expression is a set of
       constants (functions, modules, applications or  releases).  If  the  named  type  is  more
       general than the expression type, say Mod and Fun respectively, then the interpretation of
       the cast expression is the set of modules that  have  at  least  one  of  their  functions
       mentioned  in the interpretation of the expression. If the named type is more special than
       the expression type, say Fun and Mod, then the  interpretation  is  the  set  of  all  the
       functions  of  the  modules  (in  modules  mode, the conversion is partial since the local
       functions are not known). The conversions to  and  from  applications  and  releases  work
       analogously.  For  instance,  (App) "xref_.*" : Mod returns all applications containing at
       least one module such that xref_ is a prefix of the module name.

       Now assume that the interpretation of Expression is a set of calls. If the named  type  is
       more   general  than  the  expression  type,  say  Mod  and  Fun  respectively,  then  the
       interpretation of the cast expression  is  the  set  of  calls  (M1,  M2)  such  that  the
       interpretation of the expression contains a call from some function of M1 to some function
       of M2. If the named type is more special than the expression type, say Fun and  Mod,  then
       the  interpretation is the set of all function calls (F1, F2) such that the interpretation
       of the expression contains a call (M1, M2) and F1 is a function of M1 and F2 is a function
       of  M2  (in  modules mode, there are no functions calls, so a cast to Fun always yields an
       empty set). Again, the conversions to and from applications and releases work analogously.

       The interpretation of constants and variables are sets, and those sets can be used as  the
       basis for forming new sets by the application of set operators. The syntax:

         * Expression ::= Expression BinarySetOp Expression

         * BinarySetOp ::= + | * | -

       +,  *  and - are interpreted as union, intersection and difference respectively: the union
       of two sets contains the elements of both sets; the intersection of two sets contains  the
       elements  common to both sets; and the difference of two sets contains the elements of the
       first set that are not members of the second set. The elements of the two sets must be  of
       the  same structure; for instance, a function call cannot be combined with a function. But
       if a cast operator can make the elements compatible, then the more  general  elements  are
       converted to the less general element type. For instance, M + F is equivalent to (Fun) M +
       F, and E - AE is equivalent to E - (Fun)  AE.  One  more  example:  X  *  xref  :  Mod  is
       interpreted  as  the set of functions exported by the module xref; xref : Mod is converted
       to the more special type of X (Fun, that is) yielding  all  functions  of  xref,  and  the
       intersection  with  X  (all functions exported by analyzed modules and library modules) is
       interpreted as those functions that are exported by some module and functions of xref.

       There are also unary set operators:

         * Expression ::= UnarySetOp Expression

         * UnarySetOp ::= domain | range | strict

       Recall that a call is a pair (From, To). domain applied to a set of calls  is  interpreted
       as  the  set  of  all  vertices  From,  and  range  as  the  set  of  all vertices To. The
       interpretation of the strict operator is the operand with all calls on  the  form  (A,  A)
       removed.

       The interpretation of the restriction operators is a subset of the first operand, a set of
       calls. The second operand, a set of vertices, is  converted  to  the  type  of  the  first
       operand. The syntax of the restriction operators:

         * Expression ::= Expression RestrOp Expression

         * RestrOp ::= |

         * RestrOp ::= ||

         * RestrOp ::= |||

       The interpretation in some detail for the three operators:

         |:
           The subset of calls from any of the vertices.

         ||:
           The subset of calls to any of the vertices.

         |||:
           The  subset of calls to and from any of the vertices. For all sets of calls CS and all
           sets of vertices VS, CS ||| VS  is equivalent to CS | VS * CS || VS.

       Two functions (modules, applications, releases) belong  to  the  same  strongly  connected
       component  if  they  call  each  other  (in)directly. The interpretation of the components
       operator is the set of strongly connected components of a set of calls.  The  condensation
       of  a  set  of  calls is a new set of calls between the strongly connected components such
       that there is an edge between two components if  there  is  some  constant  of  the  first
       component that calls some constant of the second component.

       The  interpretation of the of operator is a chain of calls of the second operand (a set of
       calls) that passes throw all of the vertices of the first operand (a tuple of  constants),
       in  the given order. The second operand is converted to the type of the first operand. For
       instance, the of operator can be used for finding out whether  a  function  calls  another
       function  indirectly,  and  the  chain  of calls demonstrates how. The syntax of the graph
       analyzing operators:

         * Expression ::= Expression GraphOp Expression

         * GraphOp ::= components | condensation | of

       As was mentioned before, the graph analyses  operate  on  the  digraph  representation  of
       graphs. By default, the digraph representation is created when needed (and deleted when no
       longer used), but it can also be created explicitly by use of the closure operator:

         * Expression ::= ClosureOp Expression

         * ClosureOp ::= closure

       The interpretation of the closure operator is the transitive closure of the operand.

       The restriction operators are defined for closures as well; closure E  |  xref  :  Mod  is
       interpreted  as  the  direct  or  indirect  function calls from the xref module, while the
       interpretation of E | xref : Mod is the set of direct calls from xref. If some graph is to
       be  used  in several graph analyses, it saves time to assign the digraph representation of
       the graph to a user variable, and then make sure that every  graph  analysis  operates  on
       that variable instead of the list representation of the graph.

       The  lines where functions are defined (more precisely: where the first clause begins) and
       the lines where functions are used are available in functions mode. The line numbers refer
       to  the files where the functions are defined. This holds also for files included with the
       -include and -include_lib directives, which may result in functions defined apparently  in
       the same line. The line operators are used for assigning line numbers to functions and for
       assigning sets of line numbers to function calls. The syntax is similar to the one of  the
       cast operator:

         * Expression ::= ( LineOp) Expression

         * Expression ::= ( XLineOp) Expression

         * LineOp ::= Lin | ELin | LLin | XLin

         * XLineOp ::= XXL

       The  interpretation  of  the  Lin  operator  applied to a set of functions assigns to each
       function the line number where the function is defined. Unknown functions and functions of
       library modules are assigned the number 0.

       The  interpretation  of some LineOp operator applied to a set of function calls assigns to
       each call the set of line numbers where the first function calls the second function.  Not
       all calls are assigned line numbers by all operators:

         * the Lin operator is defined for Call Graph Edges;

         * the LLin operator is defined for Local Calls.

         * the XLin operator is defined for External Calls.

         * the ELin operator is defined for Inter Call Graph Edges.

       The  Lin (LLin, XLin) operator assigns the lines where calls (local calls, external calls)
       are made. The ELin operator assigns to each call (From, To),  for  which  it  is  defined,
       every  line L such that there is a chain of calls from From to To beginning with a call on
       line L.

       The XXL operator is defined for the interpretation of any of the LineOp operators  applied
       to  a set of function calls. The result is that of replacing the function call with a line
       numbered function call, that is, each of the two functions of the call is  replaced  by  a
       pair  of  the  function  and the line where the function is defined. The effect of the XXL
       operator can be undone by the LineOp operators. For  instance,  (Lin)  (XXL)  (Lin)  E  is
       equivalent to (Lin) E.

       The +, -, * and # operators are defined for line number expressions, provided the operands
       are compatible. The LineOp operators are  also  defined  for  modules,  applications,  and
       releases;  the  operand is implicitly converted to functions. Similarly, the cast operator
       is defined for the interpretation of the LineOp operators.

       The interpretation of the counting operator is the  number  of  elements  of  a  set.  The
       operator  is  undefined  for  closures.  The  +,  - and * operators are interpreted as the
       obvious arithmetical operators when  applied  to  numbers.  The  syntax  of  the  counting
       operator:

         * Expression ::= CountOp Expression

         * CountOp ::= #

       All  binary operators are left associative; for instance, A | B || C is equivalent to (A |
       B) || C. The following is a list of all operators, in increasing order of precedence:

         * +, -

         * *

         * #

         * |, ||, |||

         * of

         * (Type)

         * closure, components, condensation, domain, range, strict

       Parentheses are used for grouping, either to  make  an  expression  more  readable  or  to
       override the default precedence of operators:

         * Expression ::= ( Expression )

       A  query  is  a non-empty sequence of statements. A statement is either an assignment of a
       user variable or an expression. The value of an assignment is the value of the right  hand
       side  expression.  It  makes  no sense to put a plain expression anywhere else but last in
       queries. The syntax of queries is summarized by these productions:

         * Query ::= Statement, ...

         * Statement ::= Assignment | Expression

         * Assignment ::= Variable := Expression | Variable = Expression

       A variable cannot be assigned a new value unless first removed. Variables assigned  to  by
       the  = operator are removed at the end of the query, while variables assigned to by the :=
       operator can only be removed by calls to forget. There are no user variables  when  module
       data  need  to  be  set up again; if any of the functions that make it necessary to set up
       module data again is called, all user variables are forgotten.

       Types

       application() = atom()
       arity() = int() | -1
       bool() = true | false
       call() = {atom(), atom()} | funcall()
       constant() = mfa() | module() | application() | release()
       directory() = string()
       file() = string()
       funcall() = {mfa(), mfa()}
       function() = atom()
       int() = integer() >= 0
       library() = atom()
       library_path() = path() | code_path
       mfa() = {module(), function(), arity()}
       mode() = functions | modules
       module() = atom()
       release() = atom()
       string_position() = int() | at_end
       variable() = atom()
       xref() = atom() | pid()

EXPORTS

       add_application(Xref, Directory [, Options]) -> {ok, application()} | Error

              Types:

                 Directory = directory()
                 Error = {error, module(), Reason}
                 Options = [Option] | Option
                 Option = {builtins, bool()}  |  {name,  application()}  |  {verbose,  bool()}  |
                 {warnings, bool()}
                 Reason   =  {application_clash,  {application(),  directory(),  directory()}}  |
                 {file_error, file(), error()} | {invalid_filename, term()}  |  {invalid_options,
                 term()} | - see also add_directory -
                 Xref = xref()

              Adds  an application, the modules of the application and module data of the modules
              to an Xref server. The modules will be members of the application. The  default  is
              to use the base name of the directory with the version removed as application name,
              but this can be overridden by the name option. Returns the name of the application.

              If the given directory has a subdirectory named  ebin,  modules  (BEAM  files)  are
              searched  for  in  that  directory, otherwise modules are searched for in the given
              directory.

              If the mode of the Xref server is functions,  BEAM  files  that  contain  no  debug
              information are ignored.

       add_directory(Xref, Directory [, Options]) -> {ok, Modules} | Error

              Types:

                 Directory = directory()
                 Error = {error, module(), Reason}
                 Modules = [module()]
                 Options = [Option] | Option
                 Option = {builtins, bool()} | {recurse, bool()} | {verbose, bool()} | {warnings,
                 bool()}
                 Reason  =  {file_error,  file(),  error()}  |   {invalid_filename,   term()}   |
                 {invalid_options,   term()}   |  {unrecognized_file,  file()}  |  -  error  from
                 beam_lib:chunks/2 -
                 Xref = xref()

              Adds the modules found in the given directory and the  modules'  data  to  an  Xref
              server. The default is not to examine subdirectories, but if the option recurse has
              the value true, modules are searched for in subdirectories on all levels as well as
              in the given directory. Returns a sorted list of the names of the added modules.

              The modules added will not be members of any applications.

              If  the  mode  of  the  Xref  server is functions, BEAM files that contain no debug
              information are ignored.

       add_module(Xref, File [, Options]) -> {ok, module()} | Error

              Types:

                 Error = {error, module(), Reason}
                 File = file()
                 Options = [Option] | Option
                 Option = {builtins, bool()} | {verbose, bool()} | {warnings, bool()}
                 Reason  =  {file_error,  file(),  error()}  |   {invalid_filename,   term()}   |
                 {invalid_options,   term()}  |  {module_clash,  {module(),  file(),  file()}}  |
                 {no_debug_info, file()} | - error from beam_lib:chunks/2 -
                 Xref = xref()

              Adds a module and its module data to an Xref server. The module will not be  member
              of any application. Returns the name of the module.

              If  the  mode  of the Xref server is functions, and the BEAM file contains no debug
              information, the error message no_debug_info is returned.

       add_release(Xref, Directory [, Options]) -> {ok, release()} | Error

              Types:

                 Directory = directory()
                 Error = {error, module(), Reason}
                 Options = [Option] | Option
                 Option = {builtins, bool()} | {name, release()} | {verbose, bool()} | {warnings,
                 bool()}
                 Reason   =  {application_clash,  {application(),  directory(),  directory()}}  |
                 {file_error, file(), error()} | {invalid_filename, term()}  |  {invalid_options,
                 term()}  |  {release_clash,  {release(), directory(), directory()}} | - see also
                 add_directory -
                 Xref = xref()

              Adds a release, the applications of the release, the modules of  the  applications,
              and  module data of the modules to an Xref server. The applications will be members
              of the release, and the modules will be members of the applications. The default is
              to  use  the base name of the directory as release name, but this can be overridden
              by the name option. Returns the name of the release.

              If the given directory has a  subdirectory  named  lib,  the  directories  in  that
              directory  are  assumed to be application directories, otherwise all subdirectories
              of the given directory are assumed to be  application  directories.  If  there  are
              several versions of some application, the one with the highest version is chosen.

              If  the  mode  of  the  Xref  server is functions, BEAM files that contain no debug
              information are ignored.

       analyze(Xref, Analysis [, Options]) -> {ok, Answer} | Error

              Types:

                 Analysis = undefined_function_calls | undefined_functions  |  locals_not_used  |
                 exports_not_used   |   deprecated_function_calls  |  {deprecated_function_calls,
                 DeprFlag} | deprecated_functions |  {deprecated_functions,  DeprFlag}  |  {call,
                 FuncSpec}  |  {use, FuncSpec} | {module_call, ModSpec} | {module_use, ModSpec} |
                 {application_call,  AppSpec}  |  {application_use,  AppSpec}  |   {release_call,
                 RelSpec} | {release_use, RelSpec}
                 Answer = [term()]
                 AppSpec = application() | [application()]
                 DeprFlag = next_version | next_major_release | eventually
                 Error = {error, module(), Reason}
                 FuncSpec = mfa() | [mfa()]
                 ModSpec = module() | [module()]
                 Options = [Option] | Option
                 Option = {verbose, bool()}
                 RelSpec = release() | [release()]
                 Reason  = {invalid_options, term()} | {parse_error, string_position(), term()} |
                 {unavailable_analysis, term()} | {unknown_analysis, term()} | {unknown_constant,
                 string()} | {unknown_variable, variable()}
                 Xref = xref()

              Evaluates a predefined analysis. Returns a sorted list without duplicates of call()
              or constant(), depending on the chosen analysis.  The  predefined  analyses,  which
              operate  on  all  analyzed  modules, are (analyses marked with (*) are available in
              functionsmode only):

                undefined_function_calls(*):
                  Returns a list of calls to undefined functions.

                undefined_functions:
                  Returns a list of undefined functions.

                locals_not_used(*):
                  Returns a list of local functions that have not been locally used.

                exports_not_used:
                  Returns a list of exported functions that have not been externally used.

                deprecated_function_calls(*):
                  Returns a list of external calls to deprecated functions.

                {deprecated_function_calls, DeprFlag}(*):
                  Returns a list of external calls to deprecated functions. If DeprFlag is  equal
                  to next_version, calls to functions to be removed in next version are returned.
                  If DeprFlag is equal to next_major_release, calls to functions to be removed in
                  next  major release are returned as well as calls to functions to be removed in
                  next version. Finally, if  DeprFlag  is  equal  to  eventually,  all  calls  to
                  functions  to  be  removed  are  returned,  including  calls to functions to be
                  removed in next version or next major release.

                deprecated_functions:
                  Returns a list of externally used deprecated functions.

                {deprecated_functions, DeprFlag}:
                  Returns a list of externally used deprecated functions. If DeprFlag is equal to
                  next_version, functions to be removed in next version are returned. If DeprFlag
                  is equal to next_major_release, functions to be removed in next  major  release
                  are  returned  as  well as functions to be removed in next version. Finally, if
                  DeprFlag is equal to eventually, all functions  to  be  removed  are  returned,
                  including functions to be removed in next version or next major release.

                {call, FuncSpec}(*):
                  Returns a list of functions called by some of the given functions.

                {use, FuncSpec}(*):
                  Returns a list of functions that use some of the given functions.

                {module_call, ModSpec}:
                  Returns a list of modules called by some of the given modules.

                {module_use, ModSpec}:
                  Returns a list of modules that use some of the given modules.

                {application_call, AppSpec}:
                  Returns a list of applications called by some of the given applications.

                {application_use, AppSpec}:
                  Returns a list of applications that use some of the given applications.

                {release_call, RelSpec}:
                  Returns a list of releases called by some of the given releases.

                {release_use, RelSpec}:
                  Returns a list of releases that use some of the given releases.

       d(Directory) -> [DebugInfoResult] | [NoDebugInfoResult] | Error

              Types:

                 Directory = directory()
                 DebugInfoResult   =  {deprecated,  [funcall()]}  |  {undefined,  [funcall()]}  |
                 {unused, [mfa()]}
                 Error = {error, module(), Reason}
                 NoDebugInfoResult = {deprecated, [mfa()]} | {undefined, [mfa()]}
                 Reason  =  {file_error,  file(),  error()}  |   {invalid_filename,   term()}   |
                 {unrecognized_file, file()} | - error from beam_lib:chunks/2 -

              The  modules  found  in  the  given  directory  are checked for calls to deprecated
              functions, calls to undefined functions, and for unused local functions.  The  code
              path is used as library path.

              If  some  of the found BEAM files contain debug information, then those modules are
              checked and a list of tuples is returned. The first element of each  tuple  is  one
              of:

                * deprecated,  the  second  element  is  a  sorted  list  of  calls to deprecated
                  functions;

                * undefined, the second element is a sorted list of calls to undefined functions;

                * unused, the second element is a sorted list of unused local functions.

              If no BEAM file contains debug information, then a list of tuples is returned.  The
              first element of each tuple is one of:

                * deprecated,  the  second element is a sorted list of externally used deprecated
                  functions;

                * undefined, the second element is a sorted list of undefined functions.

       forget(Xref) -> ok
       forget(Xref, Variables) -> ok | Error

              Types:

                 Error = {error, module(), Reason}
                 Reason = {not_user_variable, term()}
                 Variables = [variable()] | variable()
                 Xref = xref()

              forget/1 and forget/2 remove all or some of the user variables of an xref server.

       format_error(Error) -> Chars

              Types:

                 Error = {error, module(), term()}
                 Chars = [char() | Chars]

              Given the error returned by any function of this module, the function  format_error
              returns a descriptive string of the error in English. For file errors, the function
              format_error/1 in the file module is called.

       get_default(Xref) -> [{Option, Value}]
       get_default(Xref, Option) -> {ok, Value} | Error

              Types:

                 Error = {error, module(), Reason}
                 Option = builtins | recurse | verbose | warnings
                 Reason = {invalid_options, term()}
                 Value = bool()
                 Xref = xref()

              Returns the default values of one or more options.

       get_library_path(Xref) -> {ok, LibraryPath}

              Types:

                 LibraryPath = library_path()
                 Xref = xref()

              Returns the library path.

       info(Xref) -> [Info]
       info(Xref, Category) -> [{Item, [Info]}]
       info(Xref, Category, Items) -> [{Item, [Info]}]

              Types:

                 Application = [] | [application()]
                 Category = modules | applications | releases | libraries
                 Info  =  {application,  Application}  |   {builtins,   bool()}   |   {directory,
                 directory()}    |    {library_path,   library_path()}   |   {mode,   mode()}   |
                 {no_analyzed_modules,   int()}   |   {no_applications,   int()}   |   {no_calls,
                 {NoResolved,  NoUnresolved}} | {no_function_calls, {NoLocal, NoResolvedExternal,
                 NoUnresolved}}     |      {no_functions,      {NoLocal,      NoExternal}}      |
                 {no_inter_function_calls,  int()}  | {no_releases, int()} | {release, Release} |
                 {version, Version}
                 Item = module() | application() | release() | library()
                 Items = Item | [Item]
                 NoLocal = NoExternal = NoResolvedExternal, NoResolved = NoUnresolved = int()
                 Release = [] | [release()]
                 Version = [int()]
                 Xref = xref()

              The info functions return information as a list of  pairs  {Tag,  term()}  in  some
              order about the state and the module data of an Xref server.

              info/1  returns  information  with  the  following  tags  (tags marked with (*) are
              available in functions mode only):

                * library_path, the library path;

                * mode, the mode;

                * no_releases, number of releases;

                * no_applications, total number of applications (of all releases);

                * no_analyzed_modules, total number of analyzed modules;

                * no_calls (*), total number of calls (in all modules),  regarding  instances  of
                  one function call in different lines as separate calls;

                * no_function_calls (*), total number of local calls, resolved external calls and
                  unresolved calls;

                * no_functions (*), total number of local and exported functions;

                * no_inter_function_calls (*), total number of calls of the Inter Call Graph.

              info/2 and info/3 return information about all or some  of  the  analyzed  modules,
              applications,  releases  or  library  modules  of  an  Xref  server.  The following
              information is returned for every analyzed module:

                * application, an empty list if the module does not belong  to  any  application,
                  otherwise a list of the application name;

                * builtins, whether calls to BIFs are included in the module's data;

                * directory, the directory where the module's BEAM file is located;

                * no_calls  (*),  number  of  calls,  regarding instances of one function call in
                  different lines as separate calls;

                * no_function_calls (*), number of  local  calls,  resolved  external  calls  and
                  unresolved calls;

                * no_functions (*), number of local and exported functions;

                * no_inter_function_calls (*), number of calls of the Inter Call Graph;

              The following information is returned for every application:

                * directory, the directory where the modules' BEAM files are located;

                * no_analyzed_modules, number of analyzed modules;

                * no_calls (*), number of calls of the application's modules, regarding instances
                  of one function call in different lines as separate calls;

                * no_function_calls (*), number of  local  calls,  resolved  external  calls  and
                  unresolved calls of the application's modules;

                * no_functions  (*),  number of local and exported functions of the application's
                  modules;

                * no_inter_function_calls (*), number of calls of the Inter  Call  Graph  of  the
                  application's modules;

                * release,  an  empty  list  if  the  application does not belong to any release,
                  otherwise a list of the release name;

                * version, the application's version as a list  of  numbers.  For  instance,  the
                  directory   "kernel-2.6"  results  in  the  application  name  kernel  and  the
                  application version [2,6]; "kernel" yields the name kernel and the version [].

              The following information is returned for every release:

                * directory, the release directory;

                * no_analyzed_modules, number of analyzed modules;

                * no_applications, number of applications;

                * no_calls (*), number of calls of the release's modules, regarding instances  of
                  one function call in different lines as separate calls;

                * no_function_calls  (*),  number  of  local  calls,  resolved external calls and
                  unresolved calls of the release's modules;

                * no_functions (*), number of local  and  exported  functions  of  the  release's
                  modules;

                * no_inter_function_calls  (*),  number  of  calls of the Inter Call Graph of the
                  release's modules.

              The following information is returned for every library module:

                * directory, the directory where the library module's BEAM file is located.

              For every number of calls, functions etc. returned by the  no_  tags,  there  is  a
              query returning the same number. Listed below are examples of such queries. Some of
              the queries return the sum of a two or more of the no_ tags numbers. mod (app, rel)
              refers to any module (application, release).

                * no_analyzed_modules

                  * "# AM" (info/1)

                  * "# (Mod) app:App" (application)

                  * "# (Mod) rel:Rel" (release)

                * no_applications

                  * "# A" (info/1)

                * no_calls. The sum of the number of resolved and unresolved calls:

                  * "# (XLin) E + # (LLin) E" (info/1)

                  * "T = E | mod:Mod, # (LLin) T + # (XLin) T" (module)

                  * "T = E | app:App, # (LLin) T + # (XLin) T" (application)

                  * "T = E | rel:Rel, # (LLin) T + # (XLin) T" (release)

                * no_functions.  Functions  in  library modules and the functions module_info/0,1
                  are not counted by info. Assuming that "Extra := _:module_info/\"(0|1)\" +  LM"
                  has been evaluated, the sum of the number of local and exported functions are:

                  * "# (F - Extra)" (info/1)

                  * "# (F * mod:Mod - Extra)" (module)

                  * "# (F * app:App - Extra)" (application)

                  * "# (F * rel:Rel - Extra)" (release)

                * no_function_calls.  The  sum  of  the  number of local calls, resolved external
                  calls and unresolved calls:

                  * "# LC + # XC" (info/1)

                  * "# LC | mod:Mod + # XC | mod:Mod" (module)

                  * "# LC | app:App + # XC | app:App" (application)

                  * "# LC | rel:Rel + # XC | mod:Rel" (release)

                * no_inter_function_calls

                  * "# EE" (info/1)

                  * "# EE | mod:Mod" (module)

                  * "# EE | app:App" (application)

                  * "# EE | rel:Rel" (release)

                * no_releases

                  * "# R" (info/1)

       m(Module) -> [DebugInfoResult] | [NoDebugInfoResult] | Error
       m(File) -> [DebugInfoResult] | [NoDebugInfoResult] | Error

              Types:

                 DebugInfoResult  =  {deprecated,  [funcall()]}  |  {undefined,  [funcall()]}   |
                 {unused, [mfa()]}
                 Error = {error, module(), Reason}
                 File = file()
                 Module = module()
                 NoDebugInfoResult = {deprecated, [mfa()]} | {undefined, [mfa()]}
                 Reason   =   {file_error,   file(),   error()}   |   {interpreted,  module()}  |
                 {invalid_filename,  term()}  |  {cover_compiled,  module()}  |  {no_such_module,
                 module()} | - error from beam_lib:chunks/2 -

              The  given  BEAM  file  (with  or without the .beam extension) or the file found by
              calling code:which(Module) is checked for calls to deprecated functions,  calls  to
              undefined  functions,  and  for  unused  local  functions. The code path is used as
              library path.

              If the BEAM file contains debug information, then a list of tuples is returned. The
              first element of each tuple is one of:

                * deprecated,  the  second  element  is  a  sorted  list  of  calls to deprecated
                  functions;

                * undefined, the second element is a sorted list of calls to undefined functions;

                * unused, the second element is a sorted list of unused local functions.

              If the BEAM file does not contain debug information,  then  a  list  of  tuples  is
              returned. The first element of each tuple is one of:

                * deprecated,  the  second element is a sorted list of externally used deprecated
                  functions;

                * undefined, the second element is a sorted list of undefined functions.

       q(Xref, Query [, Options]) -> {ok, Answer} | Error

              Types:

                 Answer = false | [constant()] | [Call] | [Component]  |  int()  |  [DefineAt]  |
                 [CallAt] | [AllLines]
                 Call = call() | ComponentCall
                 ComponentCall = {Component, Component}
                 Component = [constant()]
                 DefineAt = {mfa(), LineNumber}
                 CallAt = {funcall(), LineNumbers}
                 AllLines = {{DefineAt, DefineAt}, LineNumbers}
                 Error = {error, module(), Reason}
                 LineNumbers = [LineNumber]
                 LineNumber = int()
                 Options = [Option] | Option
                 Option = {verbose, bool()}
                 Query = string() | atom()
                 Reason  = {invalid_options, term()} | {parse_error, string_position(), term()} |
                 {type_error,    string()}    |    {type_mismatch,    string(),    string()}    |
                 {unknown_analysis,  term()}  | {unknown_constant, string()} | {unknown_variable,
                 variable()} | {variable_reassigned, string()}
                 Xref = xref()

              Evaluates a query in the context of an Xref server, and returns the  value  of  the
              last statement. The syntax of the value depends on the expression:

                * A set of calls is represented by a sorted list without duplicates of call().

                * A  set  of  constants  is  represented  by  a sorted list without duplicates of
                  constant().

                * A set of strongly connected components is a sorted list without  duplicates  of
                  Component.

                * A  set  of calls between strongly connected components is a sorted list without
                  duplicates of ComponentCall.

                * A chain of calls is represented by a list of constant(). The list contains  the
                  From vertex of every call and the To vertex of the last call.

                * The  of operator returns false if no chain of calls between the given constants
                  can be found.

                * The value of the closure operator (the digraph representation)  is  represented
                  by the atom 'closure()'.

                * A  set  of  line  numbered  functions  is  represented by a sorted list without
                  duplicates of DefineAt.

                * A set of line numbered function calls is represented by a sorted  list  without
                  duplicates of CallAt.

                * A  set of line numbered functions and function calls is represented by a sorted
                  list without duplicates of AllLines.

              For both CallAt and AllLines it holds that for no list element  is  LineNumbers  an
              empty  list;  such  elements  have been removed. The constants of component and the
              integers of LineNumbers are sorted and without duplicates.

       remove_application(Xref, Applications) -> ok | Error

              Types:

                 Applications = application() | [application()]
                 Error = {error, module(), Reason}
                 Reason = {no_such_application, application()}
                 Xref = xref()

              Removes applications and their modules and module data from an Xref server.

       remove_module(Xref, Modules) -> ok | Error

              Types:

                 Error = {error, module(), Reason}
                 Modules = module() | [module()]
                 Reason = {no_such_module, module()}
                 Xref = xref()

              Removes analyzed modules and module data from an Xref server.

       remove_release(Xref, Releases) -> ok | Error

              Types:

                 Error = {error, module(), Reason}
                 Reason = {no_such_release, release()}
                 Releases = release() | [release()]
                 Xref = xref()

              Removes releases and their applications, modules  and  module  data  from  an  Xref
              server.

       replace_application(Xref,  Application,  Directory  [,  Options]) -> {ok, application()} |
       Error

              Types:

                 Application = application()
                 Directory = directory()
                 Error = {error, module(), Reason}
                 Options = [Option] | Option
                 Option = {builtins, bool()} | {verbose, bool()} | {warnings, bool()}
                 Reason = {no_such_application, application()} | - see also add_application -
                 Xref = xref()

              Replaces the modules of an application with other modules read from an  application
              directory. Release membership of the application is retained. Note that the name of
              the application is kept; the name of the given directory is not used.

       replace_module(Xref, Module, File [, Options]) -> {ok, module()} | Error

              Types:

                 Error = {error, module(), Reason}
                 File = file()
                 Module = module()
                 Options = [Option] | Option
                 Option = {verbose, bool()} | {warnings, bool()}
                 ReadModule = module()
                 Reason = {module_mismatch, module(), ReadModule} | {no_such_module, module()}  |
                 - see also add_module -
                 Xref = xref()

              Replaces  module  data  of  an  analyzed  module  with  data read from a BEAM file.
              Application membership of the module is retained,  and  so  is  the  value  of  the
              builtins  option of the module. An error is returned if the name of the read module
              differs from the given module.

              The update function is an  alternative  for  updating  module  data  of  recompiled
              modules.

       set_default(Xref, Option, Value) -> {ok, OldValue} | Error
       set_default(Xref, OptionValues) -> ok | Error

              Types:

                 Error = {error, module(), Reason}
                 OptionValues = [OptionValue] | OptionValue
                 OptionValue = {Option, Value}
                 Option = builtins | recurse | verbose | warnings
                 Reason = {invalid_options, term()}
                 Value = bool()
                 Xref = xref()

              Sets the default value of one or more options. The options that can be set this way
              are:

                * builtins, with initial default value false;

                * recurse, with initial default value false;

                * verbose, with initial default value false;

                * warnings, with initial default value true.

              The initial default values are set when creating an Xref server.

       set_library_path(Xref, LibraryPath [, Options]) -> ok | Error

              Types:

                 Error = {error, module(), Reason}
                 LibraryPath = library_path()
                 Options = [Option] | Option
                 Option = {verbose, bool()}
                 Reason = {invalid_options, term()} | {invalid_path, term()}
                 Xref = xref()

              Sets the library path. If the given path is a  list  of  directories,  the  set  of
              library  modules  is  determined  by  choosing  the  first module encountered while
              traversing the directories in the given order, for those modules that occur in more
              than one directory. By default, the library path is an empty list.

              The  library  path  code_path is used by the functions m/1 and d/1, but can also be
              set explicitly. Note however that the code path will be  traversed  once  for  each
              used  library  module while setting up module data. On the other hand, if there are
              only a few modules that are used but not analyzed, using code_path  may  be  faster
              than setting the library path to code:get_path().

              If  the  library  path  is  set  to  code_path,  the  set of library modules is not
              determined, and the info functions will return empty lists of library modules.

       start(NameOrOptions) -> Return

              Types:

                 NameOrOptions = Name | Options
                 Name = atom()
                 Options = [Option] | Option
                 Option = {xref_mode, mode()} | term()
                 Return = {ok, pid()} | {error, {already_started, pid()}}

              Creates an Xref server. The process may optionally be given  a  name.  The  default
              mode  is  functions.  Options  that  are  not  recognized  by Xref are passed on to
              gen_server:start/4.

       start(Name, Options) -> Return

              Types:

                 Name = atom()
                 Options = [Option] | Option
                 Option = {xref_mode, mode()} | term()
                 Return = {ok, pid()} | {error, {already_started, pid()}}

              Creates an Xref server with a given name. The default mode  is  functions.  Options
              that are not recognized by Xref are passed on to gen_server:start/4.

       stop(Xref)

              Types:

                 Xref = xref()

              Stops an Xref server.

       update(Xref [, Options]) -> {ok, Modules} | Error

              Types:

                 Error = {error, module(), Reason}
                 Modules = [module()]
                 Options = [Option] | Option
                 Option = {verbose, bool()} | {warnings, bool()}
                 Reason = {invalid_options, term()} | {module_mismatch, module(), ReadModule} | -
                 see also add_module -
                 Xref = xref()

              Replaces the module data of all analyzed modules the BEAM files of which have  been
              modified  since  last  read by an add function or update. Application membership of
              the modules is retained, and so is the value of  the  builtins  option.  Returns  a
              sorted list of the names of the replaced modules.

       variables(Xref [, Options]) -> {ok, [VariableInfo]}

              Types:

                 Options = [Option] | Option
                 Option = predefined | user | {verbose, bool()}
                 Reason = {invalid_options, term()}
                 VariableInfo = {predefined, [variable()]} | {user, [variable()]}
                 Xref = xref()

              Returns a sorted lists of the names of the variables of an Xref server. The default
              is to return the user variables only.

SEE ALSO

       beam_lib(3erl), digraph(3erl), digraph_utils(3erl), re(3erl), TOOLS User's Guide