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[DebuggingTheCompiler] Add a note about using -debug-cycles to debug request evaluator cycles. #79772

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Mar 5, 2025
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[DebuggingTheCompiler] Add a note about using -debug-cycles to debug request evaluator cycles. #79772

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20 changes: 20 additions & 0 deletions docs/DebuggingTheCompiler.md
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Expand Up @@ -219,6 +219,26 @@ passing the flag `-Xfrontend -debug-constraints`:
$ swift repl -Xfrontend -debug-constraints
1> let foo = 1

### Debugging Evaluator Cycles

When triggering code in the type checker, one can by mistake cause a cycle in
the request evaluator. The error looks as follows:

```
<unknown>:0: error: circular reference
file.swift:18:22: note: through reference here
16 |
17 | extension MyType {
18 | public static func test() -> MyType { ... }
| `- note: through reference here
19 | }
20 |
```

To determine the actual circular request that is occuring, one can pass in the
flag `-debug-cycles` to the compiler which will cause the compiler to dump out
the linear chain of requests that led to the cycle.

## Debugging on SIL Level

### Options for Dumping the SIL
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