Only compute realpath when basenames_may_differ is set

A user noted that, when sources are symlinked, gdb annotations will
print the real path, rather than the name of the symlink.

It seems to me that it is better to print the name of the file that
was actually used in the build, unless there is some reason not to.

This patch implements this, with the caveat that it will not work when
basenames-may-differ is enabled.  The way this mode is currently
implemented, returning the symbolic (not real) path is not possible.

While I think it would be good to redo the source file name cache and
perhaps integrate it with class source_cache, I haven't done so here.

Regression tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-06-14  Tom Tromey  <tromey@adacore.com>

	* source.c (find_and_open_source): Respect basenames_may_differ.

gdb/testsuite/ChangeLog
2019-06-14  Tom Tromey  <tromey@adacore.com>

	* gdb.base/annotate-symlink.exp: New file.

4 files changed, 68 insertions, 5 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index f4f5b54..87575c8 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2019-06-14  Tom Tromey  <tromey@adacore.com>
+
+	* source.c (find_and_open_source): Respect basenames_may_differ.
+
 2019-06-14  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* annotate.c (annotate_breakpoints_invalid): Make use of
diff --git a/gdb/source.c b/gdb/source.c
index 00052e6..02df15a 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -987,7 +987,10 @@ find_and_open_source (const char *filename,
       result = gdb_open_cloexec (fullname->get (), OPEN_MODE, 0);
       if (result >= 0)
 	{
-	  *fullname = gdb_realpath (fullname->get ());
+	  if (basenames_may_differ)
+	    *fullname = gdb_realpath (fullname->get ());
+	  else
+	    *fullname = gdb_abspath (fullname->get ());
 	  return scoped_fd (result);
 	}
 
@@ -1031,15 +1034,16 @@ find_and_open_source (const char *filename,
   if (rewritten_filename != NULL)
     filename = rewritten_filename.get ();
 
-  result = openp (path, OPF_SEARCH_IN_PATH | OPF_RETURN_REALPATH, filename,
-		  OPEN_MODE, fullname);
+  openp_flags flags = OPF_SEARCH_IN_PATH;
+  if (basenames_may_differ)
+    flags |= OPF_RETURN_REALPATH;
+  result = openp (path, flags, filename, OPEN_MODE, fullname);
   if (result < 0)
     {
       /* Didn't work.  Try using just the basename.  */
       p = lbasename (filename);
       if (p != filename)
-	result = openp (path, OPF_SEARCH_IN_PATH | OPF_RETURN_REALPATH, p,
-			OPEN_MODE, fullname);
+	result = openp (path, flags, p, OPEN_MODE, fullname);
     }
 
   return scoped_fd (result);
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 8219486..4d89669 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2019-06-14  Tom Tromey  <tromey@adacore.com>
 
+	* gdb.base/annotate-symlink.exp: New file.
+
+2019-06-14  Tom Tromey  <tromey@adacore.com>
+
 	* gdb.ada/set_wstr.exp: Add reassignment test.
 
 2019-06-14  Tom Tromey  <tromey@adacore.com>
diff --git a/gdb/testsuite/gdb.base/annotate-symlink.exp b/gdb/testsuite/gdb.base/annotate-symlink.exp
new file mode 100644
index 0000000..6dba2fe
--- /dev/null
+++ b/gdb/testsuite/gdb.base/annotate-symlink.exp
@@ -0,0 +1,51 @@
+# Copyright (C) 2019 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/>.
+
+standard_testfile realname-expand.c realname-expand-real.c
+
+if [is_remote host] {
+    unsupported "compiling on a remote host does not support a filename with directory."
+    return 0
+}
+
+set srcdirabs [file join [pwd] $srcdir]
+set srcfilelink [standard_output_file realname-expand-link.c]
+
+remote_exec build "ln -sf ${srcdirabs}/${subdir}/${srcfile2} $srcfilelink"
+
+if { [file type $srcfilelink] != "link" } {
+    unsupported "target directory cannot have symbolic links"
+    return -1
+}
+
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile} ${srcfilelink}" "${binfile}" \
+		  executable {debug}] != "" } {
+    untested "failed to compile"
+    return -1
+}
+
+clean_restart ${testfile}
+
+if {![runto_main]} {
+    unsupported "failed to run to main"
+    return -1
+}
+
+gdb_breakpoint func message
+
+gdb_test_no_output "set annotate 1"
+
+gdb_test "continue" \
+    "Breakpoint .* func .*realname-expand-link.c:$decimal\r\n\032\032.*realname-expand-link.c:.*"