compile - Erlang Compiler
Please see following description for synopsis
compile(3) Erlang Module Definition compile(3)
NAME
compile - Erlang Compiler
DESCRIPTION
This module provides an interface to the standard Erlang compiler. It
can generate either a new file, which contains the object code, or
return a binary, which can be loaded directly.
DATA TYPES
option() = term()
See file/2 for detailed description
forms() = term()
List of Erlang abstract or Core Erlang format representations,
as used by forms/2
EXPORTS
env_compiler_options()
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(File)
Is the same as file(File, [verbose,report_errors,report_warn-
ings]).
file(File, Options) -> CompRet
Types:
CompRet = ModRet | BinRet | ErrRet
ModRet = {ok,ModuleName} | {ok,ModuleName,Warnings}
BinRet = {ok,ModuleName,Binary} | {ok,ModuleName,Binary,Warn-
ings}
ErrRet = error | {error,Errors,Warnings}
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 suc-
ceeds 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 OTP 24, the compiler will by default also dis-
play 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 com-
pile successfully. This is useful for code generators that
want to verify the code that they emit. No code is gener-
ated. 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 guaran-
teed to fail with an exception at runtime).
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 gener-
ated 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 can-
not 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 informa-
tion available during testing, yet protecting the source
code.
Mode is the type of crypto algorithm to be used for encrypt-
ing 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.
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 dependecies 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.
'P':
Produces a listing of the parsed code, after preprocessing
and parse transforms, in the file <File>.P. No object file
is produced.
'E':
Produces a listing of the code, after all source code trans-
formations have been performed, in the file <File>.E. No
object file is produced.
'S':
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 selec-
tive receive optimizations (both successful and unsuccess-
ful). 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. This option is sup-
ported since R13B04.
{error_location,line | column}:
If the value of this flag is line, the location ErrorLoca-
tion 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, describ-
ing what it is doing.
{source,FileName}:
Overrides the source file name as presented in mod-
ule_info(compile) and stack traces.
{outdir,Dir}:
Sets a new directory for the object code. The current direc-
tory 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_trans-
form/2 to be applied to the parsed code before the code is
checked for errors.
from_abstr:
The input file is expected to contain Erlang terms repre-
senting forms in abstract format (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 assembler code (default
file suffix ".S"). Notice that the format of assembler files
is not documented, and can change between releases.
from_core:
The input file is expected to be core code (default file
suffix ".core"). Notice that the format of core 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 sce-
narios, 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 verifica-
tion 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 you have a good reason (or other 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 BIFs auto-
imported before R14A, if it is needed to call the local
function with the same name as an auto-imported BIF without
module prefix.
Note:
As from R14A and forward, the compiler resolves calls without
module prefix to local or imported functions before trying
with auto-imported BIFs. 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 guaran-
tee 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.
If warnings are turned on (option report_warnings described ear-
lier), the following options control what type of warnings that
are generated. Except from {warn_format,Verbosity}, the follow-
ing options have two forms:
* A warn_xxx form, to turn on the warning.
* A 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 num-
ber 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.
Warning:
As from beginning with R14A, the compiler no longer calls the
auto-imported BIF if the name clashes with a local or explic-
itly imported function, and a call without explicit module
name is issued. Instead, the local or imported function is
called. Still accepting nowarn_bif_clash would make a module
calling functions clashing with auto-imported BIFs compile
with both the old and new compilers, but with completely dif-
ferent semantics. This is why the option is removed.
The use of this option has always been discouraged. As from
R14A, it is an error to use it.
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.
Warning:
The use of this option has always been discouraged. As from
R14A, it is an error to use it.
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.
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 com-
piler 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 com-
piler to be deprecated.
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 equiva-
lents. 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_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_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.
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 warn-
ing for 1/0 but not for X/0, because 1/0 is a constant expres-
sion that the compiler will attempt to evaluate.
The absence of warnings does not mean that there are no remain-
ing 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 OTP 22, the option {nowarn_deprecated_function, MFAs} was
only recognized when given in the file with attribute -com-
pile(). (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 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 inter-
mediate 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 earli-
est pass takes effect.
Unrecognized options are ignored.
Both WarningList and ErrorList have the following format:
[{FileName,[ErrorInfo]}].
ErrorInfo is described later in this section. 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.
forms(Forms)
Is the same as forms(Forms, [verbose,report_errors,report_warn-
ings]).
forms(Forms, Options) -> CompRet
Types:
Forms = forms()
forms() = [erl_parse:abstract_form] | cerl:c_module()
Options = [option()]
CompRet = BinRet | ErrRet
BinRet = {ok,ModuleName,BinaryOrCode} | {ok,ModuleName,Bina-
ryOrCode,Warnings}
ModuleName = module()
BinaryOrCode = binary() | term()
ErrRet = error | {error,Errors,Warnings}
Warnings = Errors = [{file:filename(), [{erl_anno:location()
| 'none', module(), term()}]}]
Analogous to file/1, but takes a list of forms (in either Erlang
abstract or Core Erlang format representation) as first argu-
ment. 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.
format_error(ErrorDescriptor) -> chars()
Types:
ErrorDescriptor = errordesc()
Uses an ErrorDescriptor and returns a deep list of characters
that describes the error. This function is usually called
implicitly when an ErrorInfo structure (described in section
Error Information) is processed.
output_generated(Options) -> true | false
Types:
Options = [term()]
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.
noenv_file(File, Options) -> CompRet
Works like file/2, except that the environment variable ERL_COM-
PILER_OPTIONS is not consulted.
noenv_forms(Forms, Options) -> CompRet
Works like forms/2, except that the environment variable
ERL_COMPILER_OPTIONS is not consulted.
noenv_output_generated(Options) -> true | false
Types:
Options = [term()]
Works like output_generated/1, except that the environment vari-
able ERL_COMPILER_OPTIONS is not consulted.
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 out-
put_generated/2. Use the alternative functions noenv_file/2,
noenv_forms/2, or noenv_output_generated/2 if you do not want the envi-
ronment 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.
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 pre-
served, except if exceptions are generated in the inlined code. Excep-
tions 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, inlin-
ing can increase Beam stack use, which probably is detrimental to per-
formance for recursive functions.
Inlining is never default. It must be explicitly enabled with a com-
piler 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 rela-
tively 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(3) for an example and an explanation of the function
parse_transform_info/0.
ERROR INFORMATION
The ErrorInfo mentioned earlier is the standard ErrorInfo structure,
which is returned from all I/O modules. It has the following format:
{ErrorLocation, Module, ErrorDescriptor}
ErrorLocation is the atom none if the error does not correspond to a
specific location, for example, if the source file does not exist.
A string describing the error is obtained with the following call:
Module:format_error(ErrorDescriptor)
SEE ALSO
epp(3), erl_id_trans(3), erl_lint(3), beam_lib(3)
Ericsson AB compiler 8.0.4 compile(3)