[gdb/testsuite] Extend gdb.base/index-cache.exp

The test-case gdb.base/index-cache.exp uses only one source file, which
contains main.

While doing "file $exec", in set_initial_language a symbol lookup of "main" is
done, causing the symtab containing main to be expanded.

Handling of main is special, and a future optimization may skip the lookup and
expansion.

Reliably exercise:
- the lookup of main, expanding the symtab containing main, by doing
  "ptype main", and
- the lookup of another symbol, expanding a symtab not containing main, by:
  - adding another source file containing function foo, and
  - doing "ptype foo".

This triggered a segfault with target board native-extended-gdbserver, filed
as PR symtab/30712, but that seems to be fixed by a previous commit in this
series.

Tested on x86_64-linux.

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

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30712

gdb/testsuite/gdb.base/index-cache-2.c

@@ -0,0 +1,24 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023 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/>.  */
+
+extern int foo (void);
+
+int
+foo (void)
+{
+  return 0;
+}

gdb/testsuite/gdb.base/index-cache.c

@@ -15,9 +15,11 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
+extern int foo (void);
+
 int
-main ()
+main (void)
 {
-  return 0;
+  return foo ();
 }
 

gdb/testsuite/gdb.base/index-cache.exp

@@ -16,9 +16,9 @@
 # This test checks that the index-cache feature generates the expected files at
 # the expected location.
 
-standard_testfile
+standard_testfile .c -2.c
 
-if { [build_executable "failed to prepare" $testfile $srcfile \
+if { [build_executable "failed to prepare" $testfile [list $srcfile $srcfile2] \
 	  {debug ldflags=-Wl,--build-id}] } {
     return
 }
@@ -147,6 +147,12 @@ proc_with_prefix test_cache_disabled { cache_dir test_prefix } {
 	    gdb_assert "$nfiles_created == 0" "no files were created"
 
 	    check_cache_stats 0 0
+
+	    # Trigger expansion of symtab containing main, if not already done.
+	    gdb_test "ptype main" "^type = int \\(void\\)"
+
+	    # Trigger expansion of symtab not containing main.
+	    gdb_test "ptype foo" "^type = int \\(void\\)"
 	}
     }
 }
@@ -192,6 +198,12 @@ proc_with_prefix test_cache_enabled_miss { cache_dir } {
 	} else {
 	    check_cache_stats 0 0
 	}
+
+	# Trigger expansion of symtab containing main, if not already done.
+	gdb_test "ptype main" "^type = int \\(void\\)"
+
+	# Trigger expansion of symtab not containing main.
+	gdb_test "ptype foo" "^type = int \\(void\\)"
     }
 }
 
@@ -221,6 +233,12 @@ proc_with_prefix test_cache_enabled_hit { cache_dir } {
 	} else {
 	    check_cache_stats 0 0
 	}
+
+	# Trigger expansion of symtab containing main, if not already done.
+	gdb_test "ptype main" "^type = int \\(void\\)"
+
+	# Trigger expansion of symtab not containing main.
+	gdb_test "ptype foo" "^type = int \\(void\\)"
     }
 }