Stack frames are sometimes missing location in source generators

[Fresa]

Version Used:
Compiler version: '4.12.0-3.24523.10 (16f58fa)'. Language version: 12.0.

I have written a source generator that tries to catch unhandled exceptions when generating code and output it through diagnostics. This works pretty good, disregarding the shortcomings of the Visual Studio Error List and description and messageFormat.

But when compiling again with no changes, the location of the stackframes in the stacktrace of the exception is gone.

If the registered source output changes then the location is reported again on next compilation.

Steps to Reproduce:

1. Throw an exception here: https://github.com/Fresa/Kafka.Protocol/blob/e8a776639f7b8143fcfb006d01f7a2eef326c5be/Kafka.Protocol.SourceGenerator/ProtocolGenerator.cs#L757
2. Attach a debugger here: https://github.com/Fresa/Kafka.Protocol/blob/e8a776639f7b8143fcfb006d01f7a2eef326c5be/Kafka.Protocol.SourceGenerator/ProtocolGenerator.cs#L811
3. Compile once (here's a project using the generator) -> stack frame has location.
4. Compile again -> stack frame is missing location.
5. Change anything in the method at 1. and compile again -> stack frame has location again.

I've tested both in Visual Studio (Version 17.12.0) and the dotnet cli (8.0.404) with the same behavior.

Diagnostic Id: N/A

Expected Behavior:
Stack frame location is the same when no code changes.

Actual Behavior:
Stack frame location is missing when running the source generator multiple times with no changes.