[RFC] [gdb/cli] Allow source highlighting to be interrupted

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

In PR cli/30934, a problem is reported where gdb becomes unresponsive for
2m13s because the GNU source-highlight library is taking a lot of time to
annotate the source.

This is due to a problem in the library [1], for which I've posted a
patch [2], which brings down the annotation time to 3s.

However, GDB should not become unresponsive due to such a problem.

Fix this by installing a srchilite::HighlightEventListener that checks whether
^C was pressed, and if so abandons the highlighting by throwing an exception.

Abandoning the highlighting looks like this to the user:
...
$ gdb -q a.out -ex "b 56"
Reading symbols from a.out...
Breakpoint 1 at 0x400e2a: file test.cpp, line 56.
(gdb) r
Starting program: /data/vries/gdb/a.out

Breakpoint 1, Solution::numOfSubarrays (this=0x7fffffffdbcf, arr=...) at test.cpp:56
^Cwarning: Couldn't highlight source file /data/vries/gdb/test.cpp: Interrupted
56	        return (int) t;
(gdb)
...

RFC: is the warning a good idea, or overkill?

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30934

[1] https://savannah.gnu.org/bugs/?64747
[2] https://savannah.gnu.org/patch/index.php?10400
---
 gdb/source-cache.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/gdb/source-cache.c b/gdb/source-cache.c
index 77b357cb42b..bd466869276 100644
--- a/gdb/source-cache.c
+++ b/gdb/source-cache.c
@@ -37,6 +37,7 @@
 #include <sstream>
 #include <srchilite/sourcehighlight.h>
 #include <srchilite/langmap.h>
+#include <srchilite/highlighteventlistener.h>
 #endif
 
 /* The number of source files we'll cache.  */
@@ -189,6 +190,25 @@ get_language_name (enum language lang)
   return nullptr;
 }
 
+/* Class with notify function called during highlighting.  */
+
+class gdb_highlight_event_listener : public srchilite::HighlightEventListener
+{
+public:
+  void notify(const srchilite::HighlightEvent &event) override
+  {
+    if (check_quit_flag ())
+      {
+	/* Got SIGINT, interrupt highlighting, it may take too long.  */
+	throw_quit ("Interrupted");
+      }
+  }
+};
+
+/* Object with notify function called during highlighting.  */
+
+static gdb_highlight_event_listener the_gdb_highlight_event_listener;
+
 #endif /* HAVE_SOURCE_HIGHLIGHT */
 
 /* See source-cache.h.  */
@@ -247,6 +267,8 @@ source_cache::ensure (struct symtab *s)
 		{
 		  highlighter = new srchilite::SourceHighlight ("esc.outlang");
 		  highlighter->setStyleFile ("esc.style");
+		  highlighter->setHighlightEventListener
+		    (&the_gdb_highlight_event_listener);
 		}
 
 	      std::istringstream input (contents);
@@ -255,6 +277,11 @@ source_cache::ensure (struct symtab *s)
 	      contents = output.str ();
 	      already_styled = true;
 	    }
+	  catch (const gdb_exception_quit &ex)
+	    {
+	      warning (_("Failed to highlight source file %s: %s"),
+		       fullname.c_str (), ex.what ());
+	    }
 	  catch (...)
 	    {
 	      /* Source Highlight will throw an exception if

base-commit: f6ca448ab70c52e923b7010aecdf7be9c0d4d4fc
-- 
2.35.3