stepping over a function containing a throw does not work

[weinand]

• Version: 6.0.0-6.2.1
• Platform: all
• Subsystem: debugging

Save this snippet as throw.js:

function throwAndCatch() {
    try {
        throw new Object();
    }
    catch (e) {
    }
}

console.log("before");
throwAndCatch();
console.log("after");
console.log("the end");

Debug snippet with node builtin debugger:

node debug throw.js

• step over console.log("before");
• step over throwAndCatch();

Observe: the first step works fine but the second doesn't. The program runs to the end.

Commenting out the line with the throw makes stepping work.

The same problem can be observed when debugging in node-inspector or VS Code.

In node versions < 6.0 stepping was working fine.

[cjihrig]

Looks like this is an issue with the new inspector debugger as well.

[weinand]

Still a problem in 6.2.2 and 7.0.0-nightly...

[bnoordhuis]

I can confirm. If you execute breakOnException before stepping over the function, the debugger will break on the exception and you can safely step out again.

I'm 95% sure it's a V8 bug because I can make it work with the small patch below:

diff --git a/deps/v8/src/debug/debug.cc b/deps/v8/src/debug/debug.cc
index 7c76742..30f79ee 100644
--- a/deps/v8/src/debug/debug.cc
+++ b/deps/v8/src/debug/debug.cc
@@ -970,6 +970,12 @@ void Debug::PrepareStepOnThrow() {

   if (it.done()) return;  // No suitable Javascript catch handler.

+  if (last_step_action() == StepNext) {
+    it.Advance();
+    if (it.done()) return;
+    if (!it.frame()->function()->shared()->IsSubjectToDebugging()) return;
+  }
+
   FloodWithOneShot(Handle<JSFunction>(it.frame()->function()));
 }

IOW, the bug appears to be that the wrong stack frame is flooded with breakpoints. I'll see if I can turn it into a patch that I can upstream.

[hashseed]

This should be the same as crbug.com/604495 and already fixed on ToT V8?