compile(3)

NAME
compile - Erlang Compiler

DESCRIPTION

This module provides an interface to the standard Erlang compiler. It can generate either a file containing the object code or return a binary that can be loaded directly.

  Default Compiler Options

The (host operating system) environment variable ERL_COMPILER_OPTIONS can be used to give default compiler options. Its value must be a valid Erlang term. If the value is a list, it is used as is. If it is not a list, it is put into a list.

The list is appended to any options given to file/2, forms/2, and output_generated/2. Use the alternative functions noenv_file/2, noenv_forms/2, or noenv_output_generated/2 if you do not want the environment variable to be consulted, for example, if you are calling the compiler recursively from inside a parse transform.

The list can be retrieved with env_compiler_options/0.

  Order of Compiler Options

Options given in the compile() attribute in the source code take precedence over options given to the compiler, which in turn take precedence over options given in the environment.

A later compiler option takes precedence over an earlier one in the option list. Example:

    compile:file(something, [nowarn_missing_spec,warn_missing_spec]).

Warnings will be emitted for functions without specifications, unless the source code for module something contains a compile(nowarn_missing_spec) attribute.

CHANGE: In Erlang/OTP 26 and earlier, the option order was the opposite of what is described here.

  Inlining

The compiler can do function inlining within an Erlang module. Inlining means that a call to a function is replaced with the function body with the arguments replaced with the actual values. The semantics are preserved, except if exceptions are generated in the inlined code, in which case exceptions are reported as occurring in the function the body was inlined into. Also, function_clause exceptions are converted to similar case_clause exceptions.

When a function is inlined, the original function is kept if it is exported (either by an explicit export or if the option export_all was given) or if not all calls to the function are inlined.

Inlining does not necessarily improve running time. For example, inlining can increase Beam stack use, which probably is detrimental to performance for recursive functions.

Inlining is never default. It must be explicitly enabled with a compiler option or a -compile() attribute in the source module.

To enable inlining, either use the option inline to let the compiler decide which functions to inline, or {inline,[{Name,Arity},...]} to have the compiler inline all calls to the given functions. If the option is given inside a compile directive in an Erlang module, {Name,Arity} can be written as Name/Arity.

Example of explicit inlining:

    -compile({inline,[pi/0]}).
    pi() -> 3.1416.

Example of implicit inlining:

    -compile(inline).

The option {inline_size,Size} controls how large functions that are allowed to be inlined. Default is 24, which keeps the size of the inlined code roughly the same as the un-inlined version (only relatively small functions are inlined).

Example:

    %% Aggressive inlining - will increase code size.
    -compile(inline).
    -compile({inline_size,100}).

  Inlining of List Functions

The compiler can also inline various list manipulation functions from the module list in STDLIB.

This feature must be explicitly enabled with a compiler option or a -compile() attribute in the source module.

To enable inlining of list functions, use option inline_list_funcs.

The following functions are inlined:

    • lists:all/2

    • lists:any/2

    • lists:foreach/2

    • lists:map/2

    • lists:flatmap/2

    • lists:filter/2

    • lists:foldl/3

    • lists:foldr/3

    • lists:mapfoldl/3

    • lists:mapfoldr/3

  Parse Transformations

Parse transformations are used when a programmer wants to use Erlang syntax but with different semantics. The original Erlang code is then transformed into other Erlang code.

See erl_id_trans for an example and an explanation of the function parse_transform_info/0.

  Recommendations for Language Implementors

Except for Erlang, there are quite a few other languages that can run on the Erlang runtime system. Generally, such compilers produce a file or binary that is fed into the Erlang compiler. There are four ways to do that using documented functionality:

    • Erlang source code (.erl file): The file is compiled using compile:file/2 or erlc <FILE>.erl. This is the most straightforward and portable way. The main disadvantage is that it is hard or impossible to map each line of Erlang code back to the corresponding line in the original source file.

    • The abstract format: This format supports mapping every Erlang source line back to its corresponding line in the original source file. To compile from the abstract format, do one following:

        • Call compile:forms/2 to directly pass in the term representation of the abstract format.

        • Write the term representation to a file with the extension .abstr and compile that file using compile:file(<File>, [from_abstr]) or erlc <File>.abstr.

    • Core Erlang: While there is a specification for Core Erlang, certain details are left to the implementation via the primop expression. Primops can be added, deleted, or changed in any major release without notice. Note that by generating Core Erlang directly, it is possible to construct code that the Core-to-BEAM backend has never encountered before, and there are no guarantees that the final BEAM code will be safe.

    • BEAM assembly code: Strongly discouraged, as it is very hard to get right and requires continuous maintenance. New instructions are typically introduced in each major release (and sometimes old ones are removed). In particular, note that BEAM code that does not follow the correct conventions can cause the runtime system to crash (segfault).

Our recommendation is to use either the abstract format or Erlang source code.

See Also

epp, erl_expand_records, erl_id_trans, erl_lint, beam_lib

DATA TYPES

abstract_code() :: [erl_parse:abstract_form()].
bin_ret() :: {ok, module(), binary()} | {ok, module(), binary(), warnings()}.
comp_ret() :: mod_ret() | bin_ret() | err_ret().
err_ret() :: error | {error, errors(), warnings()}.
error_description() :: erl_lint:error_description().
error_info() :: erl_lint:error_info().
errors() :: [{file:filename(), [error_info()]}].
forms() :: abstract_code() | cerl:c_module().

    List of Erlang abstract or Core Erlang format representations, as used by forms/2.
mod_ret() :: {ok, module()} | {ok, module(), cerl:c_module()} | {ok, module() | [], abstract_code()} | {ok, module(), warnings()}.
option() :: atom() | {atom(), term()} | {d, atom(), term()}.

    See file/2 for detailed description.
warnings() :: [{file:filename(), [error_info()]}].

FUNCTIONS

env_compiler_options() -> [term()].

    Return compiler options given via the environment variable ERL_COMPILER_OPTIONS. If the value is a list, it is returned as is. If it is not a list, it is put into a list.
file(module() | file:filename()) -> CompRet :: comp_ret().

    Is the same as file(File, [verbose,report_errors,report_warnings]).
file(File :: module() | file:filename(), Options :: [option()] | option()) -> CompRet :: comp_ret().

    Compiles the code in the file File, which is an Erlang source code file without the .erl extension.

    Options determine the behavior of the compiler.

    Returns {ok,ModuleName} if successful, or error if there are errors. An object code file is created if the compilation succeeds without errors. It is considered to be an error if the module name in the source code is not the same as the basename of the output file.

    Available options: brief
        Restricts error and warning messages to a single line of output. As of Erlang/OTP 24, the compiler will by default also display the part of the source code that the message refers to.
    basic_validation
        This option is a fast way to test whether a module will compile successfully. This is useful for code generators that want to verify the code that they emit. No code is generated. If warnings are enabled, warnings generated by the erl_lint module (such as warnings for unused variables and functions) are also returned.

        Use option strong_validation to generate all warnings that the compiler would generate.
    strong_validation
        Similar to option basic_validation. No code is generated, but more compiler passes are run to ensure that warnings generated by the optimization passes are generated (such as clauses that will not match, or expressions that are guaranteed to fail with an exception at runtime).
    no_docs
        The compiler by default extracts documentation from -doc attributes and places them in the Docs chunk according to EEP-48.

        This option switches off the placement of -doc attributes in the Docs chunk.
    binary
        The compiler returns the object code in a binary instead of creating an object file. If successful, the compiler returns {ok,ModuleName,Binary}.
    bin_opt_info
        The compiler will emit informational warnings about binary matching optimizations (both successful and unsuccessful). For more information, see the section about bin_opt_info in the Efficiency Guide.
    {compile_info, [{atom(), term()}]}
        Allows compilers built on top of compile to attach extra compilation metadata to the compile_info chunk in the generated BEAM file.

        It is advised for compilers to remove all non-deterministic information if the deterministic option is supported and it was supplied by the user.
    compressed
        The compiler will compress the generated object code, which can be useful for embedded systems.
    debug_info
        Includes debug information in the form of Erlang Abstract Format in the debug_info chunk of the compiled beam module. Tools such as Debugger, Xref, and Cover require the debug information to be included.

        Warning: Source code can be reconstructed from the debug information. Use encrypted debug information (encrypt_debug_info) to prevent this.

        For details, see beam_lib(3).
    {debug_info, {Backend, Data}}
        Includes custom debug information in the form of a Backend module with custom Data in the compiled beam module. The given module must implement a debug_info/4 function and is responsible for generating different code representations, as described in the debug_info under beam_lib(3).

        Warning: Source code can be reconstructed from the debug information. Use encrypted debug information (encrypt_debug_info) to prevent this.

        • {debug_info_key,KeyString}
    {debug_info_key,{Mode,KeyString}}
        Includes debug information, but encrypts it so that it cannot be accessed without supplying the key. (To give option debug_info as well is allowed, but not necessary.) Using this option is a good way to always have the debug information available during testing, yet protecting the source code.

        Mode is the type of crypto algorithm to be used for encrypting the debug information. The default (and currently the only) type is des3_cbc.

        For details, see beam_lib(3).
    encrypt_debug_info
        Similar to the debug_info_key option, but the key is read from an .erlang.crypt file.

        For details, see beam_lib(3).
    deterministic
        Omit the options and source tuples in the list returned by Module:module_info(compile), and reduce the paths in stack traces to the module name alone. This option will make it easier to achieve reproducible builds.
    {feature, Feature, enable | disable}
        Enable (disable) the feature Feature during compilation. The special feature all can be used to enable (disable) all features.

        NOTE: This option has no effect when used in a -compile(..) attribute. Instead, the -feature(..) directive (described next) should be used. A feature can also be enabled (disabled) using the -feature(Feature, enable | disable). module directive. Note that this directive can only be present in a prefix of the file, before exports and function definitions. This is the preferred method of enabling and disabling features, since it is a local property of a module.
    makedep
        Produces a Makefile rule to track headers dependencies. No object file is produced.

        By default, this rule is written to <File>.Pbeam. However, if option binary is set, nothing is written and the rule is returned in Binary.

        The output will be encoded in UTF-8.

        For example, if you have the following module:

            -module(module).
            -include_lib("eunit/include/eunit.hrl").
            -include("header.hrl").

        The Makefile rule generated by this option looks as follows:

            module.beam: module.erl \
              /usr/local/lib/erlang/lib/eunit/include/eunit.hrl \
              header.hrl
    makedep_side_effect
        The dependencies are created as a side effect to the normal compilation process. This means that the object file will also be produced. This option override the makedep option.
    {makedep_output, Output}
        Writes generated rules to Output instead of the default <File>.Pbeam. Output can be a filename or an io_device(). To write to stdout, use standard_io. However, if binary is set, nothing is written to Output and the result is returned to the caller with {ok, ModuleName, Binary}.
    {makedep_target, Target}
        Changes the name of the rule emitted to Target.
    makedep_quote_target
        Characters in Target special to make(1) are quoted.
    makedep_add_missing
        Considers missing headers as generated files and adds them to the dependencies.
    makedep_phony
        Adds a phony target for each dependency.
        Produces a listing of the parsed code, after preprocessing and parse transforms, in the file <File>.P. No object file is produced.
        Produces a listing of the code, after all source code transformations have been performed, in the file <File>.E. No object file is produced.
        Produces a listing of the assembler code in the file <File>.S. No object file is produced.
    recv_opt_info
        The compiler will emit informational warnings about selective receive optimizations (both successful and unsuccessful). For more information, see the section about selective receive optimization in the Efficiency Guide.
    report_errors/report_warnings
        Causes errors/warnings to be printed as they occur.
    report
        A short form for both report_errors and report_warnings.
    return_errors
        If this flag is set, {error,ErrorList,WarningList} is returned when there are errors.
    return_warnings
        If this flag is set, an extra field, containing WarningList, is added to the tuples returned on success.
    warnings_as_errors
        Causes warnings to be treated as errors.
    {error_location,line | column}
        If the value of this flag is line, the location ErrorLocation of warnings and errors is a line number. If the value is column, ErrorLocation includes both a line number and a column number. Default is column. This option is supported since Erlang/OTP 24.0.

        If the value of this flag is column, debug information includes column information.
    return
        A short form for both return_errors and return_warnings.
    verbose
        Causes more verbose information from the compiler, describing what it is doing.
    {source,FileName}
        Overrides the source file name as presented in module_info(compile) and stack traces.
    absolute_source
        Turns the source file name (as presented in module_info(compile) and stack traces) into an absolute path, which helps external tools like perf and gdb find Erlang source code.
    {outdir,Dir}
        Sets a new directory for the object code. The current directory is used for output, except when a directory has been specified with this option.
    export_all
        Causes all functions in the module to be exported.
    {i,Dir}
        Adds Dir to the list of directories to be searched when including a file. When encountering an -include or -include_lib directive, the compiler searches for header files in the following directories:

            . ".", the current working directory of the file server

            . The base name of the compiled file

            . The directories specified using option i; the directory specified last is searched first

        • {d,Macro}
    {d,Macro,Value}
        Defines a macro Macro to have the value Value. Macro is of type atom, and Value can be any term. The default Value is true.
    {parse_transform,Module}
        Causes the parse transformation function Module:parse_transform/2 to be applied to the parsed code before the code is checked for errors.
    to_abstr
        Dumps the terms representing the abstract format, after preprocessing and parse transforms, in the file <File>.abstr. No object file is produced.
    to_exp
        Dumps the terms representing the abstract format, after all source code transformations have been performed, to the file <File>.exp. No object file is produced.
    from_abstr
        The input file is expected to contain Erlang terms representing forms in the abstract format as generated by the to_abstr option (default file suffix ".abstr"). Note that the format of such terms can change between releases.

        See also the no_lint option.
    from_asm
        The input file is expected to be BEAM assembly code as generated by the 'S' option (default file suffix ".S"). Note that the format of assembler files is not documented, and can change between releases.
    from_core
        The input file is expected to be Core Erlang code (default file suffix ".core"). Note that the exact format of Core Erlang files is not documented, and can change between releases.
    no_spawn_compiler_process
        By default, all code is compiled in a separate process which is terminated at the end of compilation. However, some tools, like Dialyzer or compilers for other BEAM languages, may already manage their own worker processes and spawning an extra process may slow the compilation down. In such scenarios, you can pass this option to stop the compiler from spawning an additional process.
    no_strict_record_tests
        This option is not recommended.

        By default, the generated code for operation Record#record_tag.field verifies that the tuple Record has the correct size for the record, and that the first element is the tag record_tag. Use this option to omit the verification code.
    no_error_module_mismatch
        Normally the compiler verifies that the module name given in the source code is the same as the base name of the output file and refuses to generate an output file if there is a mismatch. If there is a good reason for having a module name unrelated to the name of the output file, this option disables that verification (there will not even be a warning if there is a mismatch).
    {no_auto_import,[{F,A}, ...]}
        Makes the function F/A no longer being auto-imported from the erlang module, which resolves BIF name clashes. This option must be used to resolve name clashes with auto-imported BIFs that existed before Erlang/OTP R14A when calling a local function with the same name as an auto-imported BIF without module prefix.

        If the BIF is to be called, use the erlang module prefix in the call, not {no_auto_import,[{F,A}, ...]}.

        If this option is written in the source code, as a -compile directive, the syntax F/A can be used instead of {F,A}. For example:

            -compile({no_auto_import,[error/1]}).
    no_auto_import
        Do not auto-import any functions from erlang module.
    no_line_info
        Omits line number information to produce a slightly smaller output file.
    no_lint
        Skips the pass that checks for errors and warnings. Only applicable together with the from_abstr option. This is mainly for implementations of other languages on top of Erlang, which have already done their own checks to guarantee correctness of the code.

        Caveat: When this option is used, there are no guarantees that the code output by the compiler is correct and safe to use. The responsibility for correctness lies on the code or person generating the abstract format. If the code contains errors, the compiler may crash or produce unsafe code.
    {extra_chunks, [{binary(), binary()}]}
        Pass extra chunks to be stored in the .beam file. The extra chunks must be a list of tuples with a four byte binary as chunk name followed by a binary with the chunk contents. See beam_lib for more information.
    {check_ssa, Tag :: atom()}
        Parse and check assertions on the structure and content of the BEAM SSA code produced by the compiler. The Tag indicates the set of assertions to check and after which compiler pass the check is performed. This option is internal to the compiler and can be changed or removed at any time without prior warning.
    line_coverage
        Instrument the compiled code for line coverage by inserting an executable_line instruction for each executable line in the source code. By default, this instruction will be ignored when loading the code.

        To activate the executable_line instructions, the runtime system must be started with the option +JPcover to enable a coverage mode. Alternatively, code:set_coverage_mode/1 can be used to set a coverage mode before loading the code.

        The coverage information gathered by the instrumented code can be retrieved by calling code:get_coverage(line, Module).
    force_line_counters
        When combined with option line_coverage, this module will be loaded in the line_counter coverage mode, regardless of the current coverage mode in the runtime system. This option is used by cover to load cover-compiled code.

    If warnings are turned on (option report_warnings described earlier), the following options control what type of warnings that are generated. Except from {warn_format,Verbosity}, the following options have two forms:

        • warn_xxx form, to turn on the warning.

        • nowarn_xxx form, to turn off the warning.

    In the descriptions that follow, the form that is used to change the default value are listed. {warn_format, Verbosity}
        Causes warnings to be emitted for malformed format strings as arguments to io:format and similar functions.

        Verbosity selects the number of warnings:

            • 0 = No warnings

            • 1 = Warnings for invalid format strings and incorrect number of arguments

            • 2 = Warnings also when the validity cannot be checked, for example, when the format string argument is a variable.

        The default verbosity is 1. Verbosity 0 can also be selected by option nowarn_format.
    nowarn_bif_clash
        This option is removed; it generates a fatal error if used.

        To resolve BIF clashes, use explicit module names or the {no_auto_import,[F/A]} compiler directive.
    {nowarn_bif_clash, FAs}
        This option is removed; it generates a fatal error if used.

        To resolve BIF clashes, use explicit module names or the {no_auto_import,[F/A]} compiler directive.
    nowarn_export_all
        Turns off warnings for uses of the export_all option. Default is to emit a warning if option export_all is also given.
    warn_export_vars
        Emits warnings for all implicitly exported variables referred to after the primitives where they were first defined. By default, the compiler only emits warnings for exported variables referred to in a pattern.
    nowarn_shadow_vars
        Turns off warnings for "fresh" variables in functional objects or list comprehensions with the same name as some already defined variable. Default is to emit warnings for such variables.
    warn_keywords
        Emits warnings when the code contains atoms that are used as keywords in some feature. When the feature is enabled, any occurrences will lead to a syntax error. To prevent this, the atom has to be renamed or quoted.
    nowarn_unused_function
        Turns off warnings for unused local functions. Default is to emit warnings for all local functions that are not called directly or indirectly by an exported function. The compiler does not include unused local functions in the generated BEAM file, but the warning is still useful to keep the source code cleaner.
    {nowarn_unused_function, FAs}
        Turns off warnings for unused local functions like nowarn_unused_function does, but only for the mentioned local functions. FAs is a tuple {Name,Arity} or a list of such tuples.
    nowarn_deprecated_function
        Turns off warnings for calls to deprecated functions. Default is to emit warnings for every call to a function known by the compiler to be deprecated. Notice that the compiler does not know about attribute -deprecated(), but uses an assembled list of deprecated functions in Erlang/OTP. To do a more general check, the Xref tool can be used. See also xref(3) and the function xref:m/1, also accessible through the function \c:xm/1.
    {nowarn_deprecated_function, MFAs}
        Turns off warnings for calls to deprecated functions like nowarn_deprecated_function does, but only for the mentioned functions. MFAs is a tuple {Module,Name,Arity} or a list of such tuples.
    nowarn_deprecated_type
        Turns off warnings for use of deprecated types. Default is to emit warnings for every use of a type known by the compiler to be deprecated.
    nowarn_deprecated_callback
        Turns off warnings for use of deprecated callbacks. Default is to emit warnings for every use of a callback known by the compiler to be deprecated.
    nowarn_deprecated_catch
        Turns off warnings for use of old style catch expressions of the form catch Expr instead of the modern try ... catch ... end.
    warn_obsolete_bool_op
        Turns on warnings for use of the and and or boolean operators.
    nowarn_match_alias_pats
        Turns off warnings for matches that unify constructors, such as the following: m({a,B} = {Y,Z}) -> . . .
    nowarn_export_var_subexpr
        Turns off warnings for exporting variables out of subexpressions.
    nowarn_removed
        Turns off warnings for calls to functions that have been removed. Default is to emit warnings for every call to a function known by the compiler to have been recently removed from Erlang/OTP.
    {nowarn_removed, ModulesOrMFAs}
        Turns off warnings for calls to modules or functions that have been removed. Default is to emit warnings for every call to a function known by the compiler to have been recently removed from Erlang/OTP.
    nowarn_obsolete_guard
        Turns off warnings for calls to old type testing BIFs, such as pid/1 and list/1. See the Erlang Reference Manual for a complete list of type testing BIFs and their old equivalents. Default is to emit warnings for calls to old type testing BIFs.
    warn_unused_import
        Emits warnings for unused imported functions. Default is to emit no warnings for unused imported functions.
    nowarn_underscore_match
        By default, warnings are emitted when a variable that begins with an underscore is matched after being bound. Use this option to turn off this kind of warning.
    nowarn_unused_vars
        By default, warnings are emitted for unused variables, except for variables beginning with an underscore ("Prolog style warnings"). Use this option to turn off this kind of warning.
    nowarn_unused_record
        Turns off warnings for unused record definitions. Default is to emit warnings for unused locally defined records.
    {nowarn_unused_record, RecordNames}
        Turns off warnings for unused record definitions. Default is to emit warnings for unused locally defined records.
    nowarn_unused_type
        Turns off warnings for unused type declarations. Default is to emit warnings for unused local type declarations.
    nowarn_nif_inline
        By default, warnings are emitted when inlining is enabled in a module that may load NIFs, as the compiler may inline NIF fallbacks by accident. Use this option to turn off this kind of warnings.

        • warn_missing_doc | warn_missing_doc_functions | warn_missing_doc_types | warn_missing_doc_callbacks By default, warnings are not emitted when -doc attribute for an exported function, callback or type is not given. Use these option to turn on this kind of warning. warn_missing_doc is equivalent to setting all of warn_missing_doc_functions, warn_missing_doc_types and warn_missing_doc_callbacks.

        • nowarn_missing_doc | nowarn_missing_doc_functions | nowarn_missing_doc_types | nowarn_missing_doc_callbacks If warnings are enabled by warn_missing_doc, then you can use these options turn those warnings off again. nowarn_missing_doc is equivalent to setting all of nowarn_missing_doc_functions, nowarn_missing_doc_types and nowarn_missing_doc_callbacks.

        • nowarn_hidden_doc | {nowarn_hidden_doc,NAs} By default, warnings are emitted when -doc false attribute is set on a callback or referenced type. You can set nowarn_hidden_doc to suppress all those warnings, or {nowarn_hidden_doc, NAs} to suppress specific callbacks or types. NAs is a tuple {Name, Arity} or a list of such tuples.
    warn_missing_spec
        By default, warnings are not emitted when a specification (or contract) for an exported function is not given. Use this option to turn on this kind of warning.
    warn_missing_spec_documented
        By default, warnings are not emitted when a specification (or contract) for a documented function is not given. Use this option to turn on this kind of warning.
    warn_missing_spec_all
        By default, warnings are not emitted when a specification (or contract) for an exported or unexported function is not given. Use this option to turn on this kind of warning.
    nowarn_redefined_builtin_type
        By default, a warning is emitted when a built-in type is locally redefined. Use this option to turn off this kind of warning.
    {nowarn_redefined_builtin_type, Types}
        By default, a warning is emitted when a built-in type is locally redefined. Use this option to turn off this kind of warning for the types in Types, where Types is a tuple {TypeName,Arity} or a list of such tuples.
    nowarn_behaviours
        By default, warnings are emitted for issues with behaviours. Use this option to turn off all warnings of this kind.
    nowarn_conflicting_behaviours
        By default, warnings are emitted when a module opts in to multiple behaviours that share the names of one or more callback functions. Use this option to turn off this kind of warning.
    nowarn_undefined_behaviour_func
        By default, a warning is emitted when a module that uses a behaviour does not export a mandatory callback function required by that behaviour. Use this option to turn off this kind of warning.
    nowarn_undefined_behaviour
        By default, a warning is emitted when a module attempts to us an unknown behaviour. Use this option to turn off this kind of warning.
    nowarn_undefined_behaviour_callbacks
        By default, a warning is emitted when behaviour_info(callbacks) in the behaviour module returns undefined instead of a list of callback functions. Use this option to turn off this kind of warning.
    nowarn_ill_defined_behaviour_callbacks
        By default, a warning is emitted when behaviour_info(callbacks) in the behaviour module returns a badly formed list of functions. Use this option to turn off this kind of warning.
    nowarn_ill_defined_optional_callbacks
        By default, a warning is emitted when behaviour_info(optional_callbacks) in the behaviour module returns a badly formed list of functions. Use this option to turn off this kind of warning.
    nowarn_novalue
        Disable warnings for creating a native record without giving values for all fields. Note that this kind of warning is only emitted when the module name for the record is explicitly given as the current module; when no module name is given, not initializing all fields is a compilation error.
    nowarn_undefined_field
        Disable warnings for referencing field names not present in the local native record definition. This warning is emitted when accessing, matching, or updating a native record. It can also be emitted when creating a record if the module name for the record is explicitly given as the current module.
    nowarn_native_record_header
        By default, a warning is emitted when a native record is defined in a header file. You can replace a native record definition in a header file with an -import_record() directive. Use this option to turn off this kind of warning.
    nowarn_unsafe_function
        Turns off warnings for calls to unsafe functions. Default is to emit warnings for every call to a function known by the compiler to be unsafe. Notice that the compiler does not know about attribute -unsafe(), but uses an assembled list of unsafe functions in Erlang/OTP. To do a more general check, the Xref tool can be used. See also xref(3) and the function xref:m/1, also accessible through the function \c:xm/1.
    {nowarn_unsafe_function, MFAs}
        Turns off warnings for calls to unsafe functions like nowarn_unsafe_function does, but only for the mentioned functions. MFAs is a tuple {Module,Name,Arity} or a list of such tuples.
    warn_possibly_unsafe_function
        Enables warnings for functions that are unsafe when used in a certain manner.

    Other kinds of warnings are opportunistic warnings. They are generated when the compiler happens to notice potential issues during optimization and code generation.

    NOTE: The compiler does not warn for expressions that it does not attempt to optimize. For example, the compiler will emit a warning for 1/0 but not for X/0, because 1/0 is a constant expression that the compiler will attempt to evaluate. The absence of warnings does not mean that there are no remaining errors in the code.

    Opportunistic warnings can be disabled using the following options: nowarn_opportunistic
        Disable all opportunistic warnings.
    nowarn_failed
        Disable warnings for expressions that will always fail (such as atom+42).
    nowarn_ignored
        Disable warnings for expressions whose values are ignored.
    nowarn_nomatch
        Disable warnings for patterns that will never match (such as a=b) and for guards that always evaluate to false.

    NOTE: All options, except the include path ({i,Dir}), can also be given in the file with attribute -compile([Option,...]). Attribute -compile() is allowed after the function definitions.

    NOTE: Before Erlang/OTP 22, the option {nowarn_deprecated_function, MFAs} was only recognized when given in the file with attribute -compile(). (The option {nowarn_unused_function,FAs} was incorrectly documented to only work in a file, but it also worked when given in the option list.) Starting from Erlang/OTP 22, all options that can be given in the file can also be given in the option list.

    For debugging of the compiler, or for pure curiosity, the intermediate code generated by each compiler pass can be inspected. To print a complete list of the options to produce list files, type compile:options() at the Erlang shell prompt. The options are printed in the order that the passes are executed. If more than one listing option is used, the one representing the earliest pass takes effect.

    Unrecognized options are ignored.

    Both WarningList and ErrorList have the following format:

        [{FileName,[ErrorInfo]}].

    The filename is included here, as the compiler uses the Erlang pre-processor epp, which allows the code to be included in other files. It is therefore important to know to which file the location of an error or a warning refers.

    The ErrorInfo structure has the following format:

        {ErrorLocation, Module, ErrorDescriptor}

    ErrorLocation is usually the tuple {Line, Column}. If option {error_location,line} has been given, ErrorLocation is only the line number. If the error does not correspond to a specific location (for example, if the source file does not exist), ErrorLocation is the atom none.

    A string describing the error is obtained with the following call:

        Module:format_error(ErrorDescriptor)
format_error(ErrorDescription :: error_description()) -> string().

    Uses an ErrorDescriptor and returns a deep list of characters that describes the error.

    This function is usually called implicitly when an ErrorInfo structure is processed.
forms(forms()) -> CompRet :: comp_ret().

    Is the same as forms(Forms, [verbose,report_errors,report_warnings]).
forms(Forms :: forms(), Options :: [option()] | option()) -> CompRet :: comp_ret().

    Analogous to file/1, but takes a list of forms (in either Erlang abstract or Core Erlang format representation) as first argument.

    Option binary is implicit, that is, no object code file is produced. For options that normally produce a listing file, such as 'E', the internal format for that compiler pass (an Erlang term, usually not a binary) is returned instead of a binary.
noenv_file(File :: module() | file:filename(), Options :: [option()] | option()) -> comp_ret().

    Works like file/2, except that the environment variable ERL_COMPILER_OPTIONS is not consulted.
noenv_forms(Forms :: forms(), Options :: [option()] | option()) -> comp_ret().

    Works like forms/2, except that the environment variable ERL_COMPILER_OPTIONS is not consulted.
noenv_output_generated(Options :: [option()]) -> boolean().

    Works like output_generated/1, except that the environment variable ERL_COMPILER_OPTIONS is not consulted.
output_generated(Options :: [option()]) -> boolean().

    Determines whether the compiler generates a BEAM file with the given options.

    true means that a BEAM file is generated. false means that the compiler generates some listing file, returns a binary, or merely checks the syntax of the source code.