[gdb/cli] Use debug info language to pick pygments lexer

Consider the following scenario:
...
$ cat hello

int
main (void)
{
  printf ("hello\n");
  return 0;
}
$ gcc -x c hello -g
$ gdb -q -iex "maint set gnu-source-highlight enabled off" a.out
Reading symbols from a.out...
(gdb) start
Temporary breakpoint 1 at 0x4005db: file hello, line 6.
Starting program: /data/vries/gdb/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Temporary breakpoint 1, main () at hello:6
6	  printf ("hello\n");
...

This doesn't produce highlighting for line 6, because:
- pygments is used for highlighting instead of source-highlight, and
- pygments guesses the language for highlighting only based on the filename,
  which in this case doesn't give a clue.

Fix this by:
- adding a language parameter to the extension_language_ops.colorize interface,
- passing the language as found in the debug info, and
- using it in gdb.styling.colorize to pick the pygments lexer.

The new test-case gdb.python/py-source-styling-2.exp excercises a slightly
different scenario: it compiles a c++ file with a .c extension, and checks
that c++ highlighting is done instead of c highlighting.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

PR cli/30966
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30966

2 files changed, 81 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.python/py-source-styling-2.c b/gdb/testsuite/gdb.python/py-source-styling-2.c
new file mode 100644
index 0000000..aaa3d69
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-source-styling-2.c
@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2025 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main ()
+{ /* List this line.  */
+  try
+    {}
+  catch (...)
+    {}
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.python/py-source-styling-2.exp b/gdb/testsuite/gdb.python/py-source-styling-2.exp
new file mode 100644
index 0000000..b13ee1f
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-source-styling-2.exp
@@ -0,0 +1,55 @@
+# Copyright (C) 2025 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Compile a c++ file using a .c extension, and check that pygments uses c++
+# highlighting instead of c highlighting.
+
+require allow_python_tests
+
+load_lib gdb-python.exp
+
+standard_testfile py-source-styling-2.c
+
+set line_number [gdb_get_line_number "List this line."]
+
+set opts {}
+lappend opts debug
+lappend opts c++
+
+if { [build_executable "failed to build" $testfile $srcfile $opts] == -1 } {
+    return
+}
+
+clean_restart
+
+gdb_test_no_output "maint set gnu-source-highlight enabled off"
+
+gdb_load $binfile
+
+require {gdb_py_module_available pygments}
+
+with_ansi_styling_terminal {
+    gdb_test_no_output "set style enabled on"
+
+    gdb_test_multiple "list $line_number" "Styling of c++ keyword try" {
+	-re -wrap "  try\r\n.*" {
+	    # Unstyled.
+	    fail $gdb_test_name
+	}
+	-re -wrap "" {
+	    pass $gdb_test_name
+	}
+    }
+}