[RFC 4/8] Add variable name styling

[Tom Tromey <tom@tromey.com>]

This adds style support for variable names.  For the time being, this
is only done in backtraces, not in ptype or print; those places do not
use ui-out and so would need ad hoc changes.

Because "name" is a relatively common MI field name, simple name
recognition does not work for variable names.  So, this patch changes
cli-out to track the enclosing list name, and only colorize "name"
when appearing somewhere within a list named "args".

This also adds styling to the names printed for local variables in
"backtrace full".  This code does not use ui-out, so the styling is
done using the low-level API.
---
 gdb/cli-out.c       | 8 ++++++++
 gdb/cli-out.h       | 3 +++
 gdb/cli/cli-style.c | 8 ++++++++
 gdb/cli/cli-style.h | 1 +
 gdb/printcmd.c      | 7 ++++++-
 5 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/gdb/cli-out.c b/gdb/cli-out.c
index eeb3a64cbae..4a5df6d3cff 100644
--- a/gdb/cli-out.c
+++ b/gdb/cli-out.c
@@ -80,6 +80,9 @@ cli_ui_out::do_table_header (int width, ui_align alignment,
 void
 cli_ui_out::do_begin (ui_out_type type, const char *id)
 {
+  m_in_args.push_back (id != nullptr && strcmp (id, "args") == 0);
+  if (m_in_args.back ())
+    ++m_in_args_count;
 }
 
 /* Mark end of a list */
@@ -87,6 +90,9 @@ cli_ui_out::do_begin (ui_out_type type, const char *id)
 void
 cli_ui_out::do_end (ui_out_type type)
 {
+  if (m_in_args.back ())
+    --m_in_args_count;
+  m_in_args.pop_back ();
 }
 
 /* output an int field */
@@ -167,6 +173,8 @@ cli_ui_out::do_field_string (int fldno, int width, ui_align align,
 	style = &file_name_style;
       else if (!strcmp (fldname, "func") || !strcmp (fldname, "function"))
 	style = &function_name_style;
+      else if (m_in_args_count > 0 && !strcmp (fldname, "name"))
+	style = &variable_name_style;
 
       if (style != nullptr)
 	set_output_style (m_streams.back (), style->style ());
diff --git a/gdb/cli-out.h b/gdb/cli-out.h
index f701da7bf38..2d26fd419a5 100644
--- a/gdb/cli-out.h
+++ b/gdb/cli-out.h
@@ -73,6 +73,9 @@ private:
 
   std::vector<ui_file *> m_streams;
   bool m_suppress_output;
+
+  std::vector<bool> m_in_args;
+  int m_in_args_count = 0;
 };
 
 extern cli_ui_out *cli_out_new (struct ui_file *stream);
diff --git a/gdb/cli/cli-style.c b/gdb/cli/cli-style.c
index 9b210863bd3..c5828d65c26 100644
--- a/gdb/cli/cli-style.c
+++ b/gdb/cli/cli-style.c
@@ -43,6 +43,7 @@ static const char * const cli_intensities[] = {
 
 cli_style_option file_name_style (ui_file_style::GREEN);
 cli_style_option function_name_style (ui_file_style::YELLOW);
+cli_style_option variable_name_style (ui_file_style::CYAN);
 
 cli_style_option::cli_style_option (ui_file_style::color fg)
   : m_foreground (cli_colors[fg - ui_file_style::NONE]),
@@ -204,4 +205,11 @@ Configure function name colors and display intensity"),
 					    "style function",
 					    &style_set_list,
 					    &style_show_list);
+  variable_name_style.add_setshow_commands ("variable", no_class,
+					    "style variable",
+					    _("\
+Variable name display styling\n\
+Configure variable name colors and display intensity"),
+					    &style_set_list,
+					    &style_show_list);
 }
diff --git a/gdb/cli/cli-style.h b/gdb/cli/cli-style.h
index d9c00003bd4..e2840c6f490 100644
--- a/gdb/cli/cli-style.h
+++ b/gdb/cli/cli-style.h
@@ -63,5 +63,6 @@ private:
 
 extern cli_style_option file_name_style;
 extern cli_style_option function_name_style;
+extern cli_style_option variable_name_style;
 
 #endif /* CLI_STYLE_H */
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 8c999188d71..c63d567e487 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -2156,7 +2156,12 @@ print_variable_and_value (const char *name, struct symbol *var,
   if (!name)
     name = SYMBOL_PRINT_NAME (var);
 
-  fprintf_filtered (stream, "%s%s = ", n_spaces (2 * indent), name);
+  fputs_filtered (n_spaces (2 * indent), stream);
+  set_output_style (stream, variable_name_style.style ());
+  fputs_filtered (name, stream);
+  set_output_style (stream, ui_file_style ());
+  fputs_filtered (" = ", stream);
+
   TRY
     {
       struct value *val;
-- 
2.13.6