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# Filing Parser Bug Reports
Guide to provide steps for filing actionable bug reports for parser failures.
Reducing a test case requires the `swift-parser-cli` utility that you can build by checking out `swift-syntax` and running `swift build --package-path SwiftParserCLI` or openning the `SwiftParserCLI` package and building the `swift-parser-cli` target in Xcode.
## Round-Trip Failure or Parser Crash
If you encounter a case where printing the parsed syntax tree does not reproduce the original source file, that’s a round-tripping failure and is considered a serious bug in SwiftSyntax – preserving the original source is a core principle of this library. To reproduce and reduce the failure, perform the following steps
1. Reduce the failure by running
```
swift-parser-cli reduce /pth/to/file/that/does/not/roundtrip.swift
```
2. File a bug report on <https://github.com/swiftlang/swift-syntax/issues/new/choose> with the reduced source code or fix the issue yourself by following the steps in <doc:FixingBugs>.
## Parse of Valid Source Failed or Bad Diagnostic Produced
If you have source code that is parsed correctly by the current Swift compiler (and thus the old parser written in C++), but that is rejected by the new parser or if you think that a diagnostic produced by the new parser is not very helpful, perform the following steps to reduce the failure:
1. Run the following command to see the diagnostics produced by the parser
```
swift-parser-cli print-diags /path/to/file.swift
```
2. Remove as much code as possible from your test file and check if it still produces the same diagnostic.
3. File a bug report on <https://github.com/swiftlang/swift-syntax/issues/new/choose> with the reduced source code or fix the issue yourself by following the steps in <doc:FixingBugs>.
## Parse of Valid Source Code Produced an Invalid Syntax Tree
If you have valid source code that produced a syntax tree which doesn’t represent the source code’s semantics correctly, perform the following steps:
1. Run the following command to print the parsed syntax tree
```
swift-parser-cli print-tree /path/to/file.swift
```
2. Remove as much code as possible from your test file and check if it still produces the same invalid tree
3. File a bug report on <https://github.com/swiftlang/swift-syntax/issues/new/choose> with the reduced source code or fix the issue yourself by following the steps in <doc:FixingBugs>.
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