[net7 Preview1][hot reload] Adding new methods in blazor wasm asserts at debug-mono-ppdb.c:499

[lambdageek]

Repro:

1. Install .NET 7 Preview 1
2. dotnet new blazorwasm
3. dotnet build ; dotnet run ctrl-C
4. dotnet watch
5. Add this to Counter.razor:

       private static void Message(string msg)
       {
           Console.WriteLine(msg);
       }
   

   and call it from IncrementCount:

      private void IncrementCount()
       {
           Message ("clicked");
           currentCount++;
       }
   

6. Save. dotnet watch says

      dotnet watch ⌚ File changed: ./Pages/Counter.razor.
      dotnet watch 🔥 Hot reload of changes succeeded.
   

7. Click the button. Look at the JS Console:

dotnet.7.0.0-preview…6.8.47lt4znjjb.js:3 /__w/1/s/src/mono/mono/metadata/debug-mono-ppdb.c:499 <disabled>
mono_wasm_trace_logger	@	dotnet.7.0.0-preview…6.8.47lt4znjjb.js:3
_mono_wasm_trace_logger	@	dotnet.7.0.0-preview….8.47lt4znjjb.js:13
$func119	@	00978d7e:0x9788
$func2516	@	00978d7e:0xa315f
$func8431	@	00978d7e:0x1b8ecc
$func8432	@	00978d7e:0x1b8efd
$func8433	@	00978d7e:0x1b8f30
$func1073	@	00978d7e:0x59dd7
$func1886	@	00978d7e:0x8374b
$func336	@	00978d7e:0x1df3e
$func388	@	00978d7e:0x28b21
$func232	@	00978d7e:0x1a8d2
$func178	@	00978d7e:0x18c0e
$func177	@	00978d7e:0xbd23
$func7742	@	00978d7e:0x198018
$func1910	@	00978d7e:0x84364
$func1908	@	00978d7e:0x842d6
$func1272	@	00978d7e:0x65691
$func267	@	00978d7e:0x1b757
$func238	@	00978d7e:0x1ad99
$func178	@	00978d7e:0xce6d
$func177	@	00978d7e:0xbd23
$func7742	@	00978d7e:0x198018
$func1910	@	00978d7e:0x84364
$func1914	@	00978d7e:0x849d1
$mono_wasm_invoke_method	@	00978d7e:0x994f
Module._mono_wasm_invoke_method	@	dotnet.7.0.0-preview….8.47lt4znjjb.js:13
_Microsoft_AspNetCore_Components_WebAssembly__Microsoft_AspNetCore_Components_WebAssembly_Services_DefaultWebAssemblyJSRuntime_BeginInvokeDotNet	@	_Microsoft_AspNetCor…eginInvokeDotNet:26
beginInvokeDotNetFromJS	@	blazor.webassembly.js:1
b	@	blazor.webassembly.js:1
invokeMethodAsync	@	blazor.webassembly.js:1
(anonymous)	@	blazor.webassembly.js:1
invokeWhenHeapUnlocked	@	blazor.webassembly.js:1
A	@	blazor.webassembly.js:1
_	@	blazor.webassembly.js:1
dispatchGlobalEventToAllElements	@	blazor.webassembly.js:1
onGlobalEvent

[lambdageek]

It's a bad bounds check that isn't hot reload aware:

runtime/src/mono/mono/metadata/debug-mono-ppdb.c

Lines 496 to 501 in cf14a83

	if (G_UNLIKELY (method_idx - 1 >= table_info_get_rows (methodbody_table))) {
	char *method_name = mono_method_full_name (method, FALSE);
	g_error ("Method idx %d is greater than number of rows (%d) in PPDB MethodDebugInformation table, for method %s in '%s'. Likely a malformed PDB file.",
	method_idx - 1, table_info_get_rows (methodbody_table), method_name, image->name);
	g_free (method_name);
	}

The question is why wasn't htis caught in CI. and I think it's because my console tests for adding methods don't send PPDB deltas. So at least part of the work here is to update the test infra to send pdb deltas.

[lambdageek]

Ah, we need the pdb delta, but we also need to set MONO_DEBUG=gen-seq-points (or attach a debugger)

[lambdageek]

Trying the fix with a real Blazor app, doesn't seem to resolve it.

[lambdageek]

Ah, I see.
What seems to happen with blazor is that we get the initial baseline .pdb files (they're packed up as part of the debug build of a wasm app), but dotnet watch doesn't send us the deltas. But sequence points are enabled, after all, for some reason (need to track down where that's coming from).

So we end up doing a lookup for the EnC debug info, don't get any, and fall through to the baseline lookup, which asserts.

[lambdageek]

Fixed by #65973 and #65867