[syntax-errors] Irrefutable case pattern before final case #16905
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Summary -- Detects irrefutable `match` cases before the final case using a modified version of the existing `Pattern::is_irrefutable` method from the AST crate. The modified method helps to retrieve a more precise diagnostic range to match what Python 3.13 shows in the REPL. Test Plan -- New inline tests, as well as some updates to existing tests that had irrefutable patterns before the last block.
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Nice, this looks good!
We could improve the error messages as I think there are only two cases where this can occur - name and wildcard pattern. CPython provides the following error messages for the above cases:
SyntaxError: name capture 'foo' makes remaining patterns unreachableSyntaxError: wildcard makes remaining patterns unreachable
| let Stmt::Match(ast::StmtMatch { cases, .. }) = stmt else { | ||
| return; | ||
| }; |
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Should we move the match expression in check_stmt above now that we have multiple checks? That would also require updating the methods like irrefutable_match_case to accept the relevant AST node which needs to be checked like in this case it would accept StmtMatch which would also lead to a safer typed API.
Summary
Detects irrefutable
matchcases before the final case using a modified versionof the existing
Pattern::is_irrefutablemethod from the AST crate. Themodified method helps to retrieve a more precise diagnostic range to match what
Python 3.13 shows in the REPL.
Test Plan
New inline tests, as well as some updates to existing tests that had irrefutable
patterns before the last block.