Column breakpoints not working - breaking as if they were just line breakpoints

[DanTup]

While working on breakpoint resolution, I noticed that column breakpoints seem to behave as if they had no column specified.

Given the code:

void main() {
  a(a(a(a(a(a(a(a(a(a(a(a(a(a(a(a(a(null)))))))))))))))));
}

int counter = 1;
Object? a(Object? a) {
  print(counter++);
  return a;
}

And a column breakpoint added in the middle of all of the a() calls:

When I run, the debugger resolves and breaks on the innermost call to a() as if it was just a standard line breakpoint:

Here's the relevant log with annotations:

// Paused at startup

// Add breakpoint at "line":2,"column":21
[12:06:51] [General] [Info] [dart] ==> [VM] {"jsonrpc":"2.0","id":"31","method":"addBreakpointWithScriptUri","params":{"isolateId":"isolates/1999819261193331","scriptUri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart","line":2,"column":21}}
[12:06:51] [General] [Info] [dart] <== [VM] {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"BreakpointAdded","isolate":{"type":"@Isolate","id":"isolates/1999819261193331","name":"main","number":"1999819261193331","isSystemIsolate":false,"isolateGroupId":"isolateGroups/16408247551111255273"},"timestamp":1677586010986,"breakpoint":{"type":"Breakpoint","fixedId":true,"id":"breakpoints/1","enabled":true,"breakpointNumber":1,"resolved":false,"location":{"type":"UnresolvedSourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"line":2,"column":21}}}}}
[12:06:51] [General] [Info] [dart] <== [VM] {"jsonrpc":"2.0","result":{"type":"Breakpoint","fixedId":true,"id":"breakpoints/1","enabled":true,"breakpointNumber":1,"resolved":false,"location":{"type":"UnresolvedSourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart","_kind":"kernel"},"line":2,"column":21}},"id":"31"}

// Resume
[12:06:51] [General] [Info] [dart] ==> [VM] {"jsonrpc":"2.0","id":"32","method":"resume","params":{"isolateId":"isolates/1999819261193331"}}
[12:06:51] [General] [Info] [dart] <== [VM] {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"Resume","isolate":{"type":"@Isolate","id":"isolates/1999819261193331","name":"main","number":"1999819261193331","isSystemIsolate":false,"isolateGroupId":"isolateGroups/16408247551111255273"},"timestamp":1677586010994}}}
[12:06:51] [General] [Info] [dart] <== [VM] {"jsonrpc":"2.0","result":{"type":"Success"},"id":"32"}

// Brekapoint resolves to "tokenPos":48,"line":2,"column":35
[12:06:51] [General] [Info] [dart] <== [VM] {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"BreakpointResolved","isolate":{"type":"@Isolate","id":"isolates/1999819261193331","name":"main","number":"1999819261193331","isSystemIsolate":false,"isolateGroupId":"isolateGroups/16408247551111255273"},"timestamp":1677586010995,"breakpoint":{"type":"Breakpoint","fixedId":true,"id":"breakpoints/1","enabled":true,"breakpointNumber":1,"resolved":true,"location":{"type":"SourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"tokenPos":48,"line":2,"column":35}}}}}

// Breakpoint hit at "tokenPos":48,"line":2,"column":35
[12:06:51] [General] [Info] [dart] <== [VM] {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"PauseBreakpoint","isolate":{"type":"@Isolate","id":"isolates/1999819261193331","name":"main","number":"1999819261193331","isSystemIsolate":false,"isolateGroupId":"isolateGroups/16408247551111255273"},"timestamp":1677586010996,"pauseBreakpoints":[{"type":"Breakpoint","fixedId":true,"id":"breakpoints/1","enabled":true,"breakpointNumber":1,"resolved":true,"location":{"type":"SourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"tokenPos":48,"line":2,"column":35}}],"topFrame":{"type":"Frame","kind":"Regular","location":{"type":"SourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"tokenPos":48,"line":2,"column":35},"function":{"type":"@Function","fixedId":true,"id":"libraries/@18271130/functions/main","name":"main","owner":{"type":"@Library","fixedId":true,"id":"libraries/@18271130","name":"","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"static":true,"const":false,"implicit":false,"abstract":false,"location":{"type":"SourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"tokenPos":0,"endTokenPos":73,"line":1,"column":1}},"code":{"type":"@Code","fixedId":true,"id":"code/2544601bd-1169a3270","name":"[Unoptimized] main","kind":"Dart","function":{"type":"@Function","fixedId":true,"id":"libraries/@18271130/functions/main","name":"main","owner":{"type":"@Library","fixedId":true,"id":"libraries/@18271130","name":"","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"static":true,"const":false,"implicit":false,"abstract":false,"location":{"type":"SourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18271130/scripts/file%3A%2F%2F%2FUsers%2Fdanny%2FDesktop%2Fdart_sample%2Fbin%2Fcolbreakpoints.dart/18697eb12b1","uri":"file:///Users/danny/Desktop/dart_sample/bin/colbreakpoints.dart"},"tokenPos":0,"endTokenPos":73,"line":1,"column":1}}},"vars":[],"index":0}}}}

The full log is here:

full_log.txt

[jacob314]

Fyi @bkonyi

[a-siva]

//cc @derekxu16

[derekxu16]

If I try to set the inline breakpoint before starting the debug session, the breakpoint incorrectly acts like a line breakpoint. But inline breakpoints do work if I follow the following procedure:

1. Add another arbitrary line at the start of main, for example print('hi);`
2. Set a breakpoint on that
3. Start the debug session
4. Add an inline breakpoint
5. Resume the program
6. Observe that the program correctly stops at the inline breakpoint

I tried setting an inline breakpoint in a similar JavaScript program before starting the debug session, and the breakpoint did correctly behave as an inline breakpoint, so I think something can be changed in the Dart Code extension to fix that flow. Do you mind looking into this when you get the chance @DanTup?

[DanTup]

I see the same behaviour described above, but I'm not sure how the VS Code extension can fix this - the requests to the VM Service are the same in both cases (allowing for the difference in code when adding an earlier breakpoint). It seems like the VM might be doing things incorrectly if the breakpoint is set before the script is loaded - but there's no way VS Code can wait before sending the breakpoint, because by then it will have been missed. Here's the VM call for the breakpoint that isn't working right, which shows the correct column (as does the response from the VM).

[4:09:25 PM] [General] [Info] [Dart] ==> [VM] {"jsonrpc":"2.0","id":"30","method":"addBreakpointWithScriptUri","params":{"isolateId":"isolates/1512056957684895","scriptUri":"file:///C:/Dev/Test%20Projects/dart_sdk_51563/bin/dart_sdk_51563.dart","line":2,"column":21}}
[4:09:25 PM] [General] [Info] [Dart] <== [VM] {"jsonrpc":"2.0","method":"streamNotify","params":{"streamId":"Debug","event":{"type":"Event","kind":"BreakpointAdded","isolate":{"type":"@Isolate","id":"isolates/1512056957684895","name":"main","number":"1512056957684895","isSystemIsolate":false,"isolateGroupId":"isolateGroups/15225165641369050677"},"timestamp":1686582565707,"breakpoint":{"type":"Breakpoint","fixedId":true,"id":"breakpoints/1","enabled":true,"breakpointNumber":1,"resolved":false,"location":{"type":"UnresolvedSourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18266854/scripts/file%3A%2F%2F%2FC%3A%2FDev%2FTest%2520Projects%2Fdart_sdk_51563%2Fbin%2Fdart_sdk_51563.dart/188b0279af6","uri":"file:///C:/Dev/Test%20Projects/dart_sdk_51563/bin/dart_sdk_51563.dart"},"line":2,"column":21}}}}}
[4:09:25 PM] [General] [Info] [Dart] <== [VM] {"jsonrpc":"2.0","result":{"type":"Breakpoint","fixedId":true,"id":"breakpoints/1","enabled":true,"breakpointNumber":1,"resolved":false,"location":{"type":"UnresolvedSourceLocation","script":{"type":"@Script","fixedId":true,"id":"libraries/@18266854/scripts/file%3A%2F%2F%2FC%3A%2FDev%2FTest%2520Projects%2Fdart_sdk_51563%2Fbin%2Fdart_sdk_51563.dart/188b0279af6","uri":"file:///C:/Dev/Test%20Projects/dart_sdk_51563/bin/dart_sdk_51563.dart","_kind":"kernel"},"line":2,"column":21}},"id":"30"}

What's been weirder, is that if I add an additional print line before it:

Then now the breakpoint happens after all of the calls on that line instead of before:

Again, the VM service call looks fine - line 3, column 21.

[DanTup]

Fix works great, thanks @derekxu16!