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How to troubleshoot a build-time regression #67161

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Mar 7, 2023
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How to troubleshoot a build-time regression #67161

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How to troubleshoot a build-time regression
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16 changes: 16 additions & 0 deletions docs/wiki/Troubleshooting-tips.md
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Expand Up @@ -64,3 +64,19 @@ I recently had to test a [Roslyn change](https://github.com/dotnet/roslyn/pull/2
Using the 32-bit Task Manager (`%WINDIR%\SysWow64\TaskMgr.exe` so that SoS will work), right-click on the hung process to produce a `.dmp` file. You can then share the file with the team via some online drive (dropbox and the like).

![image](https://user-images.githubusercontent.com/12466233/42392334-4eed5286-8107-11e8-8212-26fa53383f19.png)

# Investigating build-time regressions

There are three significant candidates to investigate:
1. analyzer issue:
Use `/p:ReportAnalyzer=true` to add analyzer timing information to the binary log.
The binary log viewer can display that information.
2. difference in inputs:
Use `/p:Features=debug-determinism` to create an additional output file that documents all the inputs to a particular compilation.
The file is written next to the compilation output and has a `.key` suffix.
Comparing those files between slow and fast runs helps detect pertinent changes (new inputs, new references, etc).
3. compiler server issue:
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This would be #2 for me.

Inspect the binary log (search for `$message CompilerServer failed` or "Error:").
If the compiler server is having issues, there will be many such entries.
In that case, use the environment variable `set RoslynCommandLineLogFile=c:\some\dir\log.txt` to enable additional logging.
In that log, "Keep alive" entries indicate that the compiler server restarted (which we don't expect to happen very often).