mbe: Rework the `concat` metavariable expression by tgross35 · Pull Request #142975 · rust-lang/rust (original) (raw)

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Jun 24, 2025

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matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Jul 1, 2025

…ation, r=petrochenkov

mbe: Add tests and restructure metavariable expressions

Add tests that show better diagnostics, and factor concat handling to a separate function. Each commit message has further details.

This performs the nonfunctional perparation for further changes such as rust-lang#142950 and rust-lang#142975 .

rust-timer added a commit that referenced this pull request

Jul 1, 2025

Rollup merge of #143245 - tgross35:metavariable-expr-organization, r=petrochenkov

mbe: Add tests and restructure metavariable expressions

Add tests that show better diagnostics, and factor concat handling to a separate function. Each commit message has further details.

This performs the nonfunctional perparation for further changes such as #142950 and #142975 .

Give a more user-friendly diagnostic about the following:

Trailing tokens within braces, e.g. ${foo() extra}
Missing parentheses, e.g. ${foo}
Incorrect number of arguments, with a hint about correct usage.

Change to a structural diagnostic, update the valid list, and move the valid list to a note.

The current messages have the potential to be more accurate; "expected identifier or string literal" is printed in a few cases where only an identifier should be expected, and it suggests removing string literals when that might not solve the problem. Add a new diagnostic for these kind of errors that gives more context and a better description.

For count and ignore this should likely be combined with the diagnositcs for eat_dollar to produce a helpful error if they get anything other than a metavariable first argument. I am planning to do this in a followup.