[gdb/cli] Keep track of styling failures in source_cache

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.

Reviewed-By: Lancelot Six <lancelot.six@amd.com>

gdb/source-cache.c

@@ -281,7 +281,8 @@ 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);
@@ -291,7 +292,26 @@ 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);
+	      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);
 	}
     }
 

gdb/source-cache.h

@@ -66,6 +66,7 @@ public:
   {
     m_source_map.clear ();
     m_offset_cache.clear ();
+    m_no_styling_files.clear ();
   }
 
 private:
@@ -95,6 +96,9 @@ private:
   /* 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.  */