automake-1.16: Yacc and Lex
8.8 Yacc and Lex support
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Automake has somewhat idiosyncratic support for Yacc and Lex.
Automake assumes that the ‘.c’ file generated by ‘yacc’ or ‘lex’
should be named using the basename of the input file. That is, for a
Yacc source file ‘foo.y’, Automake will cause the intermediate file to
be named ‘foo.c’ (as opposed to ‘y.tab.c’, which is more traditional).
The extension of a Yacc source file is used to determine the
extension of the resulting C or C++ source and header files. Be aware
that header files are generated only when the option ‘-d’ is given to
Yacc; see below for more information about this flag, and how to specify
it. Files with the extension ‘.y’ will thus be turned into ‘.c’ sources
and ‘.h’ headers; likewise, ‘.yy’ will become ‘.cc’ and ‘.hh’, ‘.y++’
will become ‘c++’ and ‘h++’, ‘.yxx’ will become ‘.cxx’ and ‘.hxx’, and
‘.ypp’ will become ‘.cpp’ and ‘.hpp’.
Similarly, Lex source files can be used to generate C or C++; the
extensions ‘.l’, ‘.ll’, ‘.l++’, ‘.lxx’, and ‘.lpp’ are recognized.
You should never explicitly mention the intermediate (C or C++) file
in any ‘SOURCES’ variable; only list the source file.
The intermediate files generated by ‘yacc’ (or ‘lex’) will be
included in any distribution that is made. That way the user doesn’t
need to have ‘yacc’ or ‘lex’.
If a Yacc source file is seen, then your ‘configure.ac’ must define
the variable ‘YACC’. This is most easily done by invoking the macro
‘AC_PROG_YACC’ (⇒Particular Program Checks (autoconf)Particular
Programs.).
When ‘yacc’ is invoked, it is passed ‘AM_YFLAGS’ and ‘YFLAGS’. The
latter is a user variable and the former is intended for the
‘Makefile.am’ author.
‘AM_YFLAGS’ is usually used to pass the ‘-d’ option to ‘yacc’.
Automake knows what this means and will automatically adjust its rules
to update and distribute the header file built by ‘yacc -d’. Caveat:
‘automake’ recognizes ‘-d’ in ‘AM_YFLAGS’ only if it is not clustered
with other options; for example, it won’t be recognized if ‘AM_YFLAGS’
is ‘-dt’, but it will be if ‘AM_YFLAGS’ is ‘-d -t’ or ‘-t -d’.
What Automake cannot guess, though, is where this header will be
used: it is up to you to ensure the header gets built before it is first
used. Typically this is necessary in order for dependency tracking to
work when the header is included by another file. The common solution
is listing the header file in ‘BUILT_SOURCES’ (⇒Sources) as
follows.
BUILT_SOURCES = parser.h
AM_YFLAGS = -d
bin_PROGRAMS = foo
foo_SOURCES = ... parser.y ...
If a Lex source file is seen, then your ‘configure.ac’ must define
the variable ‘LEX’. You can use ‘AC_PROG_LEX’ to do this (⇒
Particular Program Checks (autoconf)Particular Programs.), but using
the ‘AM_PROG_LEX’ macro (⇒Macros) is recommended.
When ‘lex’ is invoked, it is passed ‘AM_LFLAGS’ and ‘LFLAGS’. The
latter is a user variable and the former is intended for the
‘Makefile.am’ author.
When ‘AM_MAINTAINER_MODE’ (⇒maintainer-mode) is in effect, the
rebuild rules for distributed Yacc and Lex sources are only used when
‘maintainer-mode’ is enabled, or when the files have been erased.
When Yacc or Lex sources are used, ‘automake -a’ automatically
installs an auxiliary program called ‘ylwrap’ in your package (⇒
Auxiliary Programs). This program is used by the build rules to
rename the output of these tools, and makes it possible to include
multiple ‘yacc’ (or ‘lex’) source files in a single directory. This is
necessary because Yacc’s output file name is fixed, and a parallel make
could invoke more than one instance of ‘yacc’ simultaneously.
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automake-1.16: Program Variables
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automake-1.16: C++ Support