[PATCH 4/5] Add ui_file_style::merge

[Tom Tromey <tom@tromey.com>]

This adds ui_file_style::merge, a new method allowing two styles to be
merged together.
---
 gdb/ui-style.h                  | 15 +++++++++++++++
 gdb/unittests/style-selftests.c |  8 ++++++++
 2 files changed, 23 insertions(+)

diff --git a/gdb/ui-style.h b/gdb/ui-style.h
index 52f5a5a104d..53df949bd85 100644
--- a/gdb/ui-style.h
+++ b/gdb/ui-style.h
@@ -419,6 +419,21 @@ struct ui_file_style
     return this;
   }
 
+  /* Combine STYLE with this style, returning a new merged style.  Any
+     non-"empty" attributes of STYLE override the corresponding
+     attributes of this style.  */
+  ui_file_style merge (const ui_file_style &style) const
+  {
+    ui_file_style result = *this;
+    if (!style.m_foreground.is_none ())
+      result.m_foreground = style.m_foreground;
+    if (!style.m_background.is_none ())
+      result.m_background = style.m_background;
+    result.m_intensity = style.m_intensity;
+    result.m_reverse = style.m_reverse;
+    return result;
+  }
+
   /* nullptr-terminated list of names corresponding to enum basic_color.  */
   static const std::vector<const char *> basic_color_enums;
 
diff --git a/gdb/unittests/style-selftests.c b/gdb/unittests/style-selftests.c
index 9035050bd6c..0fa8074f719 100644
--- a/gdb/unittests/style-selftests.c
+++ b/gdb/unittests/style-selftests.c
@@ -119,6 +119,14 @@ run_tests ()
   SELF_CHECK (!style.is_underline ());
   SELF_CHECK (style.is_reverse ());
   SELF_CHECK (style.to_ansi () == "\033[38;2;83;84;85;48;2;0;1;254;2;23;24;7m");
+
+  const ui_file_style redblack_style (ui_file_style::RED, ui_file_style::BLACK);
+  const ui_file_style rednone_style (ui_file_style::RED, ui_file_style::NONE);
+  const ui_file_style noneblack_style (ui_file_style::NONE, ui_file_style::BLACK);
+  SELF_CHECK (ui_file_style ().merge (redblack_style) == redblack_style);
+  SELF_CHECK (redblack_style.merge ({}) == redblack_style);
+  SELF_CHECK (rednone_style.merge (noneblack_style) == redblack_style);
+  SELF_CHECK (noneblack_style.merge (rednone_style) == redblack_style);
 }
 
 } /* namespace style */

-- 
2.49.0