gdb: improve error reporting for 'save gdb-index'

While making recent changes to 'save gdb-index' command I triggered
some errors -- of the kind a user might be expected to trigger if they
do something wrong -- and I didn't find GDB's output as helpful as it
might be.

For example:

  $ gdb -q /tmp/hello.x
  ...
  (gdb) save gdb-index /non_existing_dir
  Error while writing index for `/tmp/hello': mkstemp: No such file or directory.

That the error message mentions '/tmp/hello', which does exist, but
doesn't mention '/non_existing_dir', which doesn't is, I think,
confusing.

Also, I find the 'mkstemp' in the error message confusing for a user
facing error.  A user might not know what mkstemp means, and even if
they do, that it appears in the error message is an internal GDB
detail.  The user doesn't care what function failed, but wants to know
what was wrong with their input, and what they should do to fix
things.

Similarly, for a directory that does exist, but can't be written to:

  (gdb) save gdb-index /no_access_dir
  Error while writing index for `/tmp/hello': mkstemp: Permission denied.

In this case, the 'Permission denied' might make the user thing there
is a permissions issue with '/tmp/hello', which is not the case.

After this patch, the new errors are:

  (gdb) save gdb-index /non_existing_dir
  Error while writing index for `/tmp/hello': `/non_existing_dir': No such file or directory.

and:

  (gdb) save gdb-index /no_access_dir
  Error while writing index for `/tmp/hello': `/no_access_dir': Permission denied.

we also have:

  (gdb) save gdb-index /tmp/not_a_directory
  Error while writing index for `/tmp/hello': `/tmp/not_a_directory': Is not a directory.

I think these do a better job of guiding the user towards fixing the
problem.

I've added a new test that exercises all of these cases, and also
checks the case where a user tries to use an executable that already
contains an index in order to generate an index.  As part of the new
test I've factored out some code from ensure_gdb_index (lib/gdb.exp)
into a new proc (get_index_type), which I've then used in the new
test.  I've confirmed that all the tests that use ensure_gdb_index
still pass.

During review it was pointed out that the testsuite proc
have_index (lib/gdb.exp) is similar to the new get_index_type proc, so
I've rewritten have_index to also use get_index_type, I've confirmed
that all the tests that use have_index still pass.

Nothing that worked correctly before this patch should give an error
after this patch; I've only changed the output when the user was going
to get an error anyway.

Reviewed-By: Tom de Vries <tdevries@suse.de>
Reviewed-By: Tom Tromey <tom@tromey.com>
Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
index b4a0117..842708a 100644
--- a/gdb/dwarf2/index-write.c
+++ b/gdb/dwarf2/index-write.c
@@ -1569,6 +1569,13 @@ struct index_wip_file
   index_wip_file (const char *dir, const char *basename,
 		  const char *suffix)
   {
+    /* Validate DIR is a valid directory.  */
+    struct stat buf;
+    if (stat (dir, &buf) == -1)
+      perror_with_name (string_printf (_("`%s'"), dir).c_str ());
+    if ((buf.st_mode & S_IFDIR) != S_IFDIR)
+      error (_("`%s': Is not a directory."), dir);
+
     filename = (std::string (dir) + SLASH_STRING + basename
 		+ suffix);
 
@@ -1577,7 +1584,8 @@ struct index_wip_file
     scoped_fd out_file_fd = gdb_mkostemp_cloexec (filename_temp.data (),
 						  O_BINARY);
     if (out_file_fd.get () == -1)
-      perror_with_name (("mkstemp"));
+      perror_with_name (string_printf (_("couldn't open `%s'"),
+				       filename_temp.data ()).c_str ());
 
     out_file = out_file_fd.to_file ("wb");