gdb: style filenames in separate debug file warnings

After the commit:

  commit 6647f05df023b63bbe056e9167e9e234172fa2ca
  Date:   Tue Jan 24 18:13:38 2023 +0100

      gdb: defer warnings when loading separate debug files

It was pointed out[1] that the warnings being deferred and then later
emitted lacked styling.  The warnings lacked styling before the above
commit, but it was suggested that the filenames in these warnings
should be styled, and this commit does this.

There were a couple of previous attempts[2][3][4] to solve this
problem, but these all tried to extend the mechanism introduced in the
above commit, the deferred warnings were placed directly into a
std::vector, but now we tried to, when appropriate, style these
warnings.  The review feedback that this approach looked too complex.

So instead, this revision adds a new helper class 'deferred_warnings'
which can be used to collect a set of deferred warnings, and then emit
these deferred warnings later, if needed.  This helper class hides the
complexity, so at the point the deferred warning is created no extra
logic is required.

The deferred_warnings class will style the deferred warnings only if
gdb_stderr supports styling.  GDB's warnings are sent to gdb_stderr,
so this should ensure we only style when expected.

There was also review feedback[5] that all of the warnings should be
bundled into a single string_file, this has not been done.  I feel
pretty strongly that separate warnings should be emitted using
separate "warning" calls.  If we do end up with multiple warnings in
this case they aren't really related, one will be about looking up
debug via .gnu_debuglink, while the other will be about build-id based
lookup.  So I'd really rather keep the warnings separate.

[1] https://inbox.sourceware.org/gdb-patches/87edr9pcku.fsf@tromey.com/
[2] https://inbox.sourceware.org/gdb-patches/20230216195604.2685177-1-ahajkova@redhat.com/
[3] https://inbox.sourceware.org/gdb-patches/20230217123547.2737612-1-ahajkova@redhat.com/
[4] https://inbox.sourceware.org/gdb-patches/20230320145638.1202335-1-ahajkova@redhat.com/
[5] https://inbox.sourceware.org/gdb-patches/87o7nh1g8h.fsf@tromey.com/

Co-Authored-By: Alexandra Hájková <ahajkova@redhat.com>
Approved-By: Simon Marchi <simon.marchi@efficios.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/gdb/utils.h b/gdb/utils.h
index ad0a867..c5364fa 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -367,4 +367,56 @@ assign_return_if_changed (T &lval, const T &val)
   return true;
 }
 
+/* In some cases GDB needs to try several different solutions to a problem,
+   if any of the solutions work then as far as the user is concerned the
+   problem is solved, and GDB should continue without warnings.  However,
+   if none of the solutions work then GDB should emit any warnings that
+   occurred while trying each possible solution.
+
+   One example of this is locating separate debug info.  There are several
+   different approaches for this; following the .gnu_debuglink, a build-id
+   based lookup, or using debuginfod.  If any works, and debug info is
+   located, then the user doesn't want to see warnings from the earlier
+   approaches that were tried and failed.
+
+   However, GDB should emit all the warnings using separate calls to
+   warning -- this ensures that each warning is formatted on its own line,
+   and that any styling is emitted correctly.
+
+   This class helps with deferring warnings.  Warnings can be added to an
+   instance of this class with the 'warn' function, and all warnings can be
+   emitted with a single call to 'emit'.  */
+
+struct deferred_warnings
+{
+  /* Add a warning to the list of deferred warnings.  */
+  void warn (const char *format, ...) ATTRIBUTE_PRINTF(2,3)
+  {
+    /* Generate the warning text into a string_file.  We allow the text to
+       be styled only if gdb_stderr allows styling -- warnings are sent to
+       gdb_stderr.  */
+    string_file msg (gdb_stderr->can_emit_style_escape ());
+
+    va_list args;
+    va_start (args, format);
+    msg.vprintf (format, args);
+    va_end (args);
+
+    /* Move the text into the list of deferred warnings.  */
+    m_warnings.emplace_back (std::move (msg));
+  }
+
+  /* Emit all warnings.  */
+  void emit () const
+  {
+    for (const auto &w : m_warnings)
+      warning ("%s", w.c_str ());
+  }
+
+private:
+
+  /* The list of all deferred warnings.  */
+  std::vector<string_file> m_warnings;
+};
+
 #endif /* UTILS_H */