c++: support absolute api.location.file names

In the case a user wants to create location.hh elsewhere, it can be
helpful to define api.location.file to some possibly absolute path
such as -Dapi.location.file='"$(top_srcdir)/include/ast/location.hh"'.
Currently this does not work with `-o foo/parser.cc`, as we join foo/
and $(top_srcdir) together, the latter starting with slash.

We should not try to do that in m4, manipulating file names is quite
complex when you through Windows file name in.  Let m4 delegate this
to gnulib.

* src/scan-skel.l (at_output): Accept up to two arguments.
* data/bison.m4 (b4_output): Adjust.
* tests/skeletons.at (Fatal errors but M4 continues producing output):
Adjust to keep the error.

* data/location.cc, data/stack.hh: Leave the concatenation to @output.
* tests/output.at: Exercise api.location.file with an absolute path.

data/bison.m4

@@ -65,14 +65,16 @@ version 2.2 of Bison.])])
 ## Output.  ##
 ## -------- ##
 
-# b4_output_begin(FILE)
+# b4_output_begin(FILE1, FILE2)
-# ---------------------
+# -----------------------------
 # Enable output, i.e., send to diversion 0, expand after "#", and
 # generate the tag to output into FILE.  Must be followed by EOL.
+# FILE is FILE1 concatenated to FILE2.  FILE2 can be empty, or be
+# absolute: do the right thing.
 m4_define([b4_output_begin],
 [m4_changecom()
 m4_divert_push(0)dnl
-@output(m4_unquote([$1])@)@dnl
+@output(m4_unquote([$1])@,m4_unquote([$2])@)@dnl
 ])
 
 

data/location.cc

@@ -305,7 +305,7 @@ m4_define([b4_location_define],
 
 
 m4_ifdef([b4_position_file], [[
-]b4_output_begin([b4_dir_prefix[]b4_position_file])[
+]b4_output_begin([b4_dir_prefix], [b4_position_file])[
 // Starting with Bison 3.2, this file is useless: the structure it
 // used to define is now defined in "]b4_location_file[".
 //
@@ -323,7 +323,7 @@ m4_ifdef([b4_position_file], [[
 
 
 m4_ifdef([b4_location_file], [[
-]b4_output_begin([b4_dir_prefix[]b4_location_file])[
+]b4_output_begin([b4_dir_prefix], [b4_location_file])[
 ]b4_copyright([Locations for Bison parsers in C++])[
 
 /**

data/stack.hh

@@ -140,7 +140,7 @@ m4_define([b4_stack_define],
 
 
 m4_ifdef([b4_stack_file],
-[b4_output_begin([b4_dir_prefix[]b4_stack_file])[
+[b4_output_begin([b4_dir_prefix], [b4_stack_file])[
 // Starting with Bison 3.2, this file is useless: the structure it
 // used to define is now defined with the parser itself.
 //

src/scan-skel.l

@@ -29,8 +29,9 @@
 #define FLEX_PREFIX(Id) skel_ ## Id
 #include <src/flex-scanner.h>
 
-#include <dirname.h>
 #include <error.h>
+#include <dirname.h>
+#include <path-join.h>
 #include <quotearg.h>
 
 #include <src/complain.h>
@@ -236,14 +237,14 @@ at_complain (int argc, char *argv[], char **out_namep, int *out_linenop)
 static void
 at_output (int argc, char *argv[], char **out_namep, int *out_linenop)
 {
-  if (2 < argc)
+  if (3 < argc)
     fail_for_at_directive_too_many_args (argv[0]);
   if (*out_namep)
     {
       free (*out_namep);
       xfclose (yyout);
     }
-  *out_namep = xstrdup (argv[1]);
+  *out_namep = xpath_join (argv[1], 2 < argc ? argv[2] : NULL);
   output_file_name_check (out_namep, true);
   /* If there were errors, do not generate the output.  */
   yyout = xfopen (complaint_status ? "/dev/null" : *out_namep, "w");

tests/output.at

@@ -45,9 +45,13 @@ done
 [$2[
 %%
 foo: %empty {};
-]])[
+]])
 
-]AT_BISON_CHECK([$3 $1], [$5], [], [ignore])[
+# There is not AT_DATA_UNQUOTED.
+AT_CHECK([$PERL -pi -e 's{\$at_dir}'"{$at_group_dir}g" $1])
+
+
+AT_BISON_CHECK([$3 $1], [$5], [], [ignore])[
 # Ignore the files non-generated files
 ]AT_CHECK_FILES([$4], [$1])[
 ]$6[
@@ -206,8 +210,10 @@ AT_CHECK_OUTPUT([foo.yy],
                 [%skeleton "lalr1.cc" %defines %locations %define api.location.file "foo.loc.hh"],
                 [],
                 [foo.loc.hh foo.tab.cc foo.tab.hh])
+
+# Absolute paths.
 AT_CHECK_OUTPUT([foo.yy],
-                [%skeleton "lalr1.cc" %defines %define api.stack.file none %locations %define api.location.file "foo.loc.hh"],
+                [%skeleton "lalr1.cc" %defines %locations %define api.location.file "$at_dir/foo.loc.hh"],
                 [],
                 [foo.loc.hh foo.tab.cc foo.tab.hh])
 

tests/skeletons.at

@@ -306,7 +306,7 @@ use strict;
 my $M4 = "m4";
 my $DNL = "d"."nl";
 print "${M4}_divert_push(0)$DNL\n";
-print '@output(@,@)', "\n";
+print '@output(@,@,@)', "\n";
 (print "garbage"x10, "\n") for (1..1000);
 print "${M4}_divert_pop(0)\n";
 ]])