[PATCH v2 3/4] [gdb/cli] Keep track of styling failures in source_cache

[Tom de Vries <tdevries@suse.de>]

In source_cache::ensure, keep track of which files failed to be styled, and
don't attempt to style them again in case the file dropped out of the cache.

Tested on x86_64-linux.
---
 gdb/source-cache.c | 24 ++++++++++++++++++++++--
 gdb/source-cache.h |  4 ++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/gdb/source-cache.c b/gdb/source-cache.c
index 9757721e932..f8c98d7e23f 100644
--- a/gdb/source-cache.c
+++ b/gdb/source-cache.c
@@ -285,7 +285,8 @@ source_cache::ensure (struct symtab *s)
       return false;
     }
 
-  if (source_styling && gdb_stdout->can_emit_style_escape ())
+  if (source_styling && gdb_stdout->can_emit_style_escape ()
+      && m_no_styling_files.count (fullname) == 0)
     {
       bool already_styled
 	= try_source_highlight (contents, s->language (), fullname);
@@ -295,7 +296,26 @@ source_cache::ensure (struct symtab *s)
 	  gdb::optional<std::string> ext_contents;
 	  ext_contents = ext_lang_colorize (fullname, contents);
 	  if (ext_contents.has_value ())
-	    contents = std::move (*ext_contents);
+	    {
+	      contents = std::move (*ext_contents);
+	      already_styled = true;
+	    }
+	}
+
+      if (!already_styled)
+	{
+	  /* Styling failed.  Styling can fail for instance for these
+	     reasons:
+	     - the language is not supported.
+	     - the language cannot not be auto-detected from the file name.
+	     - no stylers available.
+
+	     Since styling failed, don't try styling the file again after it
+	     drops from the cache.
+
+	     Note that clearing the source cache also clears
+	     m_no_styling_files.  */
+	  m_no_styling_files.insert (fullname);
 	}
     }
 
diff --git a/gdb/source-cache.h b/gdb/source-cache.h
index bec6598ff9f..f1d30b43ce0 100644
--- a/gdb/source-cache.h
+++ b/gdb/source-cache.h
@@ -66,6 +66,7 @@ class source_cache
   {
     m_source_map.clear ();
     m_offset_cache.clear ();
+    m_no_styling_files.clear ();
   }
 
 private:
@@ -95,6 +96,9 @@ class source_cache
   /* The file offset cache.  The key is the full name of the source
      file.  */
   std::unordered_map<std::string, std::vector<off_t>> m_offset_cache;
+
+  /* The list of files where styling failed.  */
+  std::unordered_set<std::string> m_no_styling_files;
 };
 
 /* The global source cache.  */
-- 
2.35.3