emacs/doc/misc/flymake.texi

\input texinfo   @c -*-texinfo-*-
@comment %**start of header
@setfilename ../../info/flymake.info
@set VERSION 0.3
@set UPDATED April 2004
@settitle GNU Flymake @value{VERSION}
@include ../emacs/docstyle.texi
@syncodeindex pg cp
@comment %**end of header

@copying
This manual is for GNU Flymake (version @value{VERSION}, @value{UPDATED}),
which is a universal on-the-fly syntax checker for GNU Emacs.

Copyright @copyright{} 2004--2017 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''.

(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.''
@end quotation
@end copying

@dircategory Emacs misc features
@direntry
* Flymake: (flymake).           A universal on-the-fly syntax checker.
@end direntry

@titlepage
@title GNU Flymake
@subtitle for version @value{VERSION}, @value{UPDATED}
@author Pavel Kobiakov(@email{pk_at_work@@yahoo.com}) and João Távora.
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top GNU Flymake
@insertcopying
@end ifnottex

@menu
* Overview of Flymake::
* Installing Flymake::
* Using Flymake::
* Extending Flymake::
* The legacy Proc backend::
* GNU Free Documentation License::
* Index::
@end menu

@node Overview of Flymake
@chapter Overview
@cindex Overview of Flymake

Flymake is a universal on-the-fly buffer checker implemented as an
Emacs minor mode. When enabled, Flymake visually annotates the buffer
with diagnostic information coming from one or more different sources,
or @emph{backends}.

Historically, Flymake used to accept diagnostics from a single, albeit
reasonably flexible, backend.

This backend isn't (yet) obsolete and so is still available as a
fallback and active by default(@pxref{The legacy Proc backend}). It works by
selecting a syntax check tool from a preconfigured list (compiler for
C++ files, @code{perl} for perl files, etc.), and executing it in the
background, passing it a temporary file which is a copy of the current
buffer, and parsing the output for known error/warning message
patterns.

Flymake annotates the buffer by highlighting problematic buffer
regions with a special space. It also displays an overall buffer
status in the mode line.  Status information displayed by Flymake
contains totals for different types of diagnostics.

@code{flymake-goto-next-error} and @code{flymake-goto-prev-error} are
commands that allow easy navigation to the next/previous erroneous
line, respectively. If might be a good idea to map them to @kbd{M-n}
and @kbd{M-p} in @code{flymake-mode}, by adding to your init file:

@lisp
(define-key flymake-mode-map (kbd "M-n") 'flymake-goto-next-error)
(define-key flymake-mode-map (kbd "M-p") 'flymake-goto-prev-error)
@end lisp

Syntax check is done ``on-the-fly''.  It is started whenever

@itemize @bullet
@item @code{flymake-mode} is started;
@item a newline character is added to the buffer;
@item some changes were made to the buffer more than @code{0.5} seconds ago (the
delay is configurable).
@end itemize

Flymake is a universal syntax checker in the sense that it's easily
extended to support new backends.  @xref{Customizable variables}.

@node Installing Flymake
@chapter Installing
@cindex Installing Flymake

Flymake is included with Emacs and its main commands, like
@code{flymake-mode}, are autoloaded. This means there is usually
nothing to do by way of installation.

@node Using Flymake
@chapter Using Flymake
@cindex Using Flymake

@menu
* Flymake mode::
* Running the syntax check::
* Navigating to error lines::   @c * Viewing error messages::
* Syntax check statuses::
* Troubleshooting::
* Customizable variables::
@end menu

@node Flymake mode
@section Flymake mode
@cindex flymake-mode

Flymake is an Emacs minor mode.  To use Flymake, you
must first activate @code{flymake-mode} by using the
@code{flymake-mode} function.

Instead of manually activating @code{flymake-mode}, you can configure
Flymake to automatically enable @code{flymake-mode} upon opening any
file for which syntax check is possible.  To do so, place the following
line in @code{.emacs}:

@lisp
(add-hook 'find-file-hook 'flymake-find-file-hook)
@end lisp

@node Running the syntax check
@section Running the syntax check
@cindex Manually starting the syntax check

When @code{flymake-mode} is active, syntax check is started
automatically on any of the three conditions mentioned above.  Syntax
check can also be started manually by using the @code{flymake-start}
function.

@node Navigating to error lines
@section Navigating to error lines
@cindex Navigating to error lines

After syntax check is completed, lines for which at least one error or
warning has been reported are highlighted, and total number of errors
and warning is shown in the mode line.  Use the following functions to
navigate the highlighted lines.

@multitable @columnfractions 0.25 0.75

@item @code{flymake-goto-next-error}
@tab Moves point to the next erroneous line, if any.

@item @code{flymake-goto-prev-error}
@tab Moves point to the previous erroneous line.

@end multitable

If the user option @code{flymake-wrap-around} is active
(@pxref{Customizable variables}), these functions treat diagnostics
as a linked list.  Therefore, @code{flymake-goto-next-error} will go
to the first diagnostic when invoked in the end of the buffer.

@node Syntax check statuses
@section Syntax check statuses
@cindex Syntax check statuses

After syntax check is finished, its status is displayed in the mode line.
The following statuses are defined.

@multitable @columnfractions 0.25 0.75
@item @code{Wait}
@tab  Some flymake backends haven't reported since the last time they
where questioned.

@item @code{!}
@tab All the configured Flymake backends have disabled themselves.
Left-clicking the ``Flymake'' mode line indicator beings the user
@code{*Flymake log*} buffer where these situations may be investigated

@item @code{?}
@tab There are no configured Flymake backends in
@code{flymake-diagnostic-functions}.

@item @emph{[nerrors nwarnings]}
@tab Normal operation, number of errors/warnings found by the syntax
check process.
@end multitable

@node Troubleshooting
@section Troubleshooting
@cindex Logging
@cindex Troubleshooting

Flymake uses a simple logging facility for indicating important points
in the control flow.  The logging facility sends logging messages to
the @file{*Flymake log*} buffer.  The information logged can be used for
resolving various problems related to Flymake.

Logging output is controlled by the Emacs @code{warning-minimum-log-level}
and @code{warning-minimum-level} variables.

@node Customizable variables
@section Customizable variables
@cindex Customizable variables

This section summarizes variables used for the configuration of the
Flymake user interface.

@table @code
@item flymake-no-changes-timeout
If any changes are made to the buffer, syntax check is automatically
started after @code{flymake-no-changes-timeout} seconds.

@item flymake-start-syntax-check-on-newline
A boolean flag indicating whether to start syntax check after a
newline character is added to the buffer.

@item flymake-error
A custom face for highlighting regions for which an error has been
reported.

@item flymake-warning
A custom face for highlighting regions for which a warning has been
reported.

@item flymake-note
A custom face for highlighting regions for which a note has been
reported.

@item flymake-error-bitmap
A bitmap used in the fringe to mark lines for which an error has
been reported.

@item flymake-warning-bitmap
A bitmap used in the fringe to mark lines for which a warning has
been reported.

@item flymake-fringe-indicator-position
Which fringe (if any) should show the warning/error bitmaps.

@item flymake-wrap-around
If non-nil, moving to errors with @code{flymake-goto-next-error} and
@code{flymake-goto-prev-error} wraps around buffer boundaries.

@end table

@node Extending Flymake
@chapter Extending Flymake
@cindex Extending Flymake

@node The legacy Proc backend
@chapter The legacy ``Proc'' backend
@cindex The legacy Proc backend

@menu
* Proc customization variables::
* Adding support for a new syntax check tool::
* Implementation overview::
* Making a temporary copy::
* Locating a master file::
* Getting the include directories::
* Locating the buildfile::
* Starting the syntax check process::
* Parsing the output::
* Interaction with other modes::
@end menu

The backend @code{flymake-proc-legacy-backend} was originally designed
to be extended for supporting new syntax check tools and error message
patterns. It is also controlled by its own set of customization variables

@node Proc customization variables
@section Customization variables for the Proc backend
@cindex Proc customization variables

@table @code
@item flymake-proc-allowed-file-name-masks
A list of @code{(filename-regexp, init-function, cleanup-function
getfname-function)} for configuring syntax check tools.  @xref{Adding
support for a new syntax check tool}.

@item flymake-proc-master-file-dirs
A list of directories for searching a master file.  @xref{Locating a
master file}.

@item flymake-proc-get-project-include-dirs-function
A function used for obtaining a list of project include dirs (C/C++
specific).  @xref{Getting the include directories}.

@item flymake-proc-master-file-count-limit
@itemx flymake-proc-check-file-limit
Used when looking for a master file.  @xref{Locating a master file}.

@item flymake-proc-err-line-patterns
Patterns for error/warning messages in the form @code{(regexp file-idx
line-idx col-idx err-text-idx)}.  @xref{Parsing the output}.

@item flymake-proc-diagnostic-type-pred
A function to classify a diagnostic text as particular type of
error. Should be a function taking an error text and returning one of
the symbols indexing @code{flymake-diagnostic-types-alist}. If non-nil
is returned but there is no such symbol in that table, a warning is
assumed. If nil is returned, an error is assumed. Can also be a
regular expression that should match only warnings.  This variable
replaces the old @code{flymake-warning-re} and
@code{flymake-warning-predicate}.

@item flymake-proc-compilation-prevents-syntax-check
A flag indicating whether compilation and syntax check of the same
file cannot be run simultaneously.
@end table

@node Adding support for a new syntax check tool
@section Adding support for a new syntax check tool
@cindex Adding support for a new syntax check tool

@menu
* Example---Configuring a tool called directly::
* Example---Configuring a tool called via make::
@end menu

Syntax check tools are configured using the
@code{flymake-proc-allowed-file-name-masks} list.  Each item of this list
has the following format:

@lisp
(filename-regexp, init-function, cleanup-function, getfname-function)
@end lisp

@table @code
@item filename-regexp
This field is used as a key for locating init/cleanup/getfname
functions for the buffer.  Items in
@code{flymake-proc-allowed-file-name-masks} are searched sequentially.
The first item with @code{filename-regexp} matching buffer filename is
selected.  If no match is found, @code{flymake-mode} is switched off.

@item init-function
@code{init-function} is required to initialize the syntax check,
usually by creating a temporary copy of the buffer contents.  The
function must return @code{(list cmd-name arg-list)}.  If
@code{init-function} returns null, syntax check is aborted, by
@code{flymake-mode} is not switched off.

@item cleanup-function
@code{cleanup-function} is called after the syntax check process is
complete and should take care of proper deinitialization, which is
usually deleting a temporary copy created by the @code{init-function}.

@item getfname-function
This function is used for translating filenames reported by the syntax
check tool into ``real'' filenames.  Filenames reported by the tool
will be different from the real ones, as actually the tool works with
the temporary copy.  In most cases, the default implementation
provided by Flymake, @code{flymake-proc-get-real-file-name}, can be
used as @code{getfname-function}.

@end table

To add support for a new syntax check tool, write corresponding
@code{init-function}, and, optionally @code{cleanup-function} and
@code{getfname-function}.  If the format of error messages reported by
the new tool is not yet supported by Flymake, add a new entry to
the @code{flymake-proc-err-line-patterns} list.

The following sections contain some examples of configuring Flymake
support for various syntax check tools.

@node Example---Configuring a tool called directly
@subsection Example---Configuring a tool called directly
@cindex Adding support for perl

In this example, we will add support for @code{perl} as a syntax check
tool.  @code{perl} supports the @code{-c} option which does syntax
checking.

First, we write the @code{init-function}:

@lisp
(defun flymake-proc-perl-init ()
  (let* ((temp-file (flymake-proc-init-create-temp-buffer-copy
                     'flymake-proc-create-temp-inplace))
         (local-file (file-relative-name
                      temp-file
                      (file-name-directory buffer-file-name))))
    (list "perl" (list "-wc " local-file))))
@end lisp

@code{flymake-proc-perl-init} creates a temporary copy of the buffer
contents with the help of
@code{flymake-proc-init-create-temp-buffer-copy}, and builds an appropriate
command line.

Next, we add a new entry to the
@code{flymake-proc-allowed-file-name-masks}:

@lisp
(setq flymake-proc-allowed-file-name-masks
      (cons '(".+\\.pl$"
              flymake-proc-perl-init
              flymake-proc-simple-cleanup
              flymake-proc-get-real-file-name)
            flymake-proc-allowed-file-name-masks))
@end lisp

Note that we use standard @code{cleanup-function} and
@code{getfname-function}.

Finally, we add an entry to @code{flymake-proc-err-line-patterns}:

@lisp
(setq flymake-proc-err-line-patterns
      (cons '("\\(.*\\) at \\([^ \n]+\\) line \\([0-9]+\\)[,.\n]"
              2 3 nil 1)
            flymake-proc-err-line-patterns))
@end lisp

@node Example---Configuring a tool called via make
@subsection Example---Configuring a tool called via make
@cindex Adding support for C (gcc+make)

In this example we will add support for C files syntax checked by
@command{gcc} called via @command{make}.

We're not required to write any new functions, as Flymake already has
functions for @command{make}.  We just add a new entry to the
@code{flymake-proc-allowed-file-name-masks}:

@lisp
(setq flymake-proc-allowed-file-name-masks
      (cons '(".+\\.c$"
              flymake-proc-simple-make-init
              flymake-proc-simple-cleanup
              flymake-proc-get-real-file-name)
            flymake-proc-allowed-file-name-masks))
@end lisp

@code{flymake-proc-simple-make-init} builds the following @command{make}
command line:

@lisp
(list "make"
      (list "-s" "-C"
            base-dir
            (concat "CHK_SOURCES=" source)
            "SYNTAX_CHECK_MODE=1"
            "check-syntax"))
@end lisp

@code{base-dir} is a directory containing @code{Makefile}, see @ref{Locating the buildfile}.

Thus, @code{Makefile} must contain the @code{check-syntax} target.  In
our case this target might look like this:

@verbatim
check-syntax:
	gcc -o /dev/null -S ${CHK_SOURCES} || true
@end verbatim

@noindent
The format of error messages reported by @command{gcc} is already
supported by Flymake, so we don't have to add a new entry to
@code{flymake-err-line-patterns}.  Note that if you are using
Automake, you may want to replace @code{gcc} with the standard
Automake variable @code{COMPILE}:

@verbatim
check-syntax:
	$(COMPILE) -o /dev/null -S ${CHK_SOURCES} || true
@end verbatim

@node Implementation overview
@section Implementation overview
@cindex Syntax check models
@cindex Master file

@code{flymake-proc-legacy-backend} saves a copy of the buffer in a
temporary file in the buffer's directory (or in the system temp
directory, for java files), creates a syntax check command and
launches a process with this command.  The output is parsed using a
list of error message patterns, and error information (file name, line
number, type and text) is saved.  After the process has finished,
Flymake highlights erroneous lines in the buffer using the accumulated
error information.

Syntax check is considered possible if there's an entry in
@code{flymake-proc-allowed-file-name-masks} matching buffer's filename and
its @code{init-function} returns non-@code{nil} value.

Two syntax check modes are distinguished:

@enumerate

@item
Buffer can be syntax checked in a standalone fashion, that is, the
file (its temporary copy, in fact) can be passed over to the compiler to
do the syntax check.  Examples are C/C++ (.c, .cpp) and Java (.java)
sources.

@item
Buffer can be syntax checked, but additional file, called master file,
is required to perform this operation.  A master file is a file that
includes the current file, so that running a syntax check tool on it
will also check syntax in the current file.  Examples are C/C++ (.h,
.hpp) headers.

@end enumerate

These modes are handled inside init/cleanup/getfname functions, see
@ref{Adding support for a new syntax check tool}.

The Proc backend contains implementations of all functionality
required to support different syntax check modes described above
(making temporary copies, finding master files, etc.), as well as some
tool-specific (routines for Make, Ant, etc.)@: code.


@node Making a temporary copy
@section Making a temporary copy
@cindex Temporary copy of the buffer
@cindex Master file

After the possibility of the syntax check has been determined, a
temporary copy of the current buffer is made so that the most recent
unsaved changes could be seen by the syntax check tool.  Making a copy
is quite straightforward in a standalone case (mode @code{1}), as it's
just saving buffer contents to a temporary file.

Things get trickier, however, when master file is involved, as it
requires to

@itemize @bullet
@item locate a master file
@item patch it to include the current file using its new (temporary)
name.
@end itemize

Locating a master file is discussed in the following section.

Patching just changes all appropriate lines of the master file so that they
use the new (temporary) name of the current file.  For example, suppose current
file name is @code{file.h}, the master file is @code{file.cpp}, and
it includes current file via @code{#include "file.h"}.  Current file's copy
is saved to file @code{file_flymake.h}, so the include line must be
changed to @code{#include "file_flymake.h"}.  Finally, patched master file
is saved to @code{file_flymake_master.cpp}, and the last one is passed to
the syntax check tool.

@node Locating a master file
@section Locating a master file
@cindex Master file

Master file is located in two steps.

First, a list of possible master files is built.  A simple name
matching is used to find the files.  For a C++ header @code{file.h},
the Proc backend searches for all @code{.cpp} files in the directories
whose relative paths are stored in a customizable variable
@code{flymake-proc-master-file-dirs}, which usually contains something
like @code{("." "./src")}.  No more than
@code{flymake-proc-master-file-count-limit} entries is added to the
master file list.  The list is then sorted to move files with names
@code{file.cpp} to the top.

Next, each master file in a list is checked to contain the appropriate
include directives.  No more than @code{flymake-proc-check-file-limit} of each
file are parsed.

For @code{file.h}, the include directives to look for are
@code{#include "file.h"}, @code{#include "../file.h"}, etc.  Each
include is checked against a list of include directories
(see @ref{Getting the include directories}) to be sure it points to the
correct @code{file.h}.

First matching master file found stops the search.  The master file is then
patched and saved to disk.  In case no master file is found, syntax check is
aborted, and corresponding status (!) is reported in the mode line.

@node Getting the include directories
@section Getting the include directories
@cindex Include directories (C/C++ specific)

Two sets of include directories are distinguished: system include directories
and project include directories.  The former is just the contents of the
@code{INCLUDE} environment variable.  The latter is not so easy to obtain,
and the way it can be obtained can vary greatly for different projects.
Therefore, a customizable variable
@code{flymake-proc-get-project-include-dirs-function} is used to provide the
way to implement the desired behavior.

The default implementation, @code{flymake-proc-get-project-include-dirs-imp},
uses a @command{make} call.  This requires a correct base directory, that is, a
directory containing a correct @file{Makefile}, to be determined.

As obtaining the project include directories might be a costly operation, its
return value is cached in the hash table.  The cache is cleared in the beginning
of every syntax check attempt.

@node Locating the buildfile
@section Locating the buildfile
@cindex Locating the buildfile
@cindex buildfile, locating
@cindex Makefile, locating

The Proc backend can be configured to use different tools for
performing syntax checks.  For example, it can use direct compiler
call to syntax check a perl script or a call to @command{make} for a
more complicated case of a @code{C/C++} source.  The general idea is
that simple files, like perl scripts and html pages, can be checked by
directly invoking a corresponding tool.  Files that are usually more
complex and generally used as part of larger projects, might require
non-trivial options to be passed to the syntax check tool, like
include directories for C++.  The latter files are syntax checked
using some build tool, like Make or Ant.

All Make configuration data is usually stored in a file called
@code{Makefile}.  To allow for future extensions, flymake uses a notion of
buildfile to reference the 'project configuration' file.

Special function, @code{flymake-proc-find-buildfile} is provided for locating buildfiles.
Searching for a buildfile is done in a manner similar to that of searching
for possible master files.
@ignore
A customizable variable
@code{flymake-proc-buildfile-dirs} holds a list of relative paths to the
buildfile.  They are checked sequentially until a buildfile is found.
@end ignore
In case there's no build file, syntax check is aborted.

Buildfile values are also cached.

@node Starting the syntax check process
@section Starting the syntax check process
@cindex Syntax check process

The command line (command name and the list of arguments) for
launching a process is returned by the initialization function.  The
Proc backend then just starts an asynchronous process and configures a
process filter and sentinel, which are used for processing the output
of the syntax check tool.  When exiting Emacs, running processes will
be killed without prompting the user.

@node Parsing the output
@section Parsing the output
@cindex Parsing the output

The output generated by the syntax check tool is parsed in the process
filter/sentinel using the error message patterns stored in the
@code{flymake-proc-err-line-patterns} variable.  This variable contains a
list of items of the form @code{(regexp file-idx line-idx
err-text-idx)}, used to determine whether a particular line is an
error message and extract file name, line number and error text,
respectively.  Error type (error/warning) is also guessed by matching
error text with the '@code{^[wW]arning}' pattern.  Anything that was not
classified as a warning is considered an error.  Type is then used to
sort error menu items, which shows error messages first.

The Proc backend is also able to interpret error message patterns
missing err-text-idx information.  This is done by merely taking the
rest of the matched line (@code{(substring line (match-end 0))}) as
error text.  This trick allows making use of a huge collection of
error message line patterns from @code{compile.el}.  All these error
patterns are appended to the end of
@code{flymake-proc-err-line-patterns}.

The error information obtained is saved in a buffer local
variable.  The buffer for which the process output belongs is
determined from the process-id@w{}->@w{}buffer mapping updated
after every process launch/exit.

@node Interaction with other modes
@section Interaction with other modes
@cindex Interaction with other modes
@cindex Interaction with compile mode

The only mode the Proc backend currently knows about is
@code{compile}.

The Proc backend can be configured to not start syntax check if it
thinks the compilation is in progress, by testing the
@code{compilation-in-progress} variable.  The reason why this might be
useful is saving CPU time in case both syntax check and compilation
are very CPU intensive.  The original reason for adding this feature,
though, was working around a locking problem with MS Visual C++
compiler.  The variable in question is
@code{flymake-proc-compilation-prevents-syntax-check}.

The Proc backend also provides an alternative command for starting
compilation, @code{flymake-proc-compile}. It just kills all the active
syntax check processes before calling @code{compile}.

@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include doclicense.texi

@node Index
@unnumbered Index

@printindex cp

@bye