Confusing error message in macro expansion: “error: expected expression, found 1 + 1”
#71039
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A-diagnostics
Area: Messages for errors, warnings, and lints
A-macros
Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)
C-enhancement
Category: An issue proposing an enhancement or a PR with one.
D-papercut
Diagnostics: An error or lint that needs small tweaks.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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estebank
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Jul 31, 2023
…ment Partially address rust-lang#71039.
estebank
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Oct 10, 2023
…ment Partially address rust-lang#71039.
bors
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Oct 10, 2023
More detail when expecting expression but encountering bad macro argument Partially address rust-lang#71039. ``` error: expected expression, found `1 + 1` --> $DIR/trace_faulty_macros.rs:49:37 | LL | (let $p:pat = $e:expr) => {test!(($p,$e))}; | -- this is interpreted as pattern `1 + 1` (in expansion #2) ... LL | (($p:pat, $e:pat)) => {let $p = $e;}; | ^^ expected expression ... LL | test!(let x = 1+1); | ------------------ | | | | | this is interpreted as expression `1 + 1` (in expansion #1) | in this macro invocation | = note: this error originates in the macro `test` (in Nightly builds, run with -Z macro-backtrace for more info) ```
bors
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Oct 12, 2023
More detail when expecting expression but encountering bad macro argument Partially address rust-lang#71039. ``` error: expected expression, found `1 + 1` --> $DIR/trace_faulty_macros.rs:49:37 | LL | (let $p:pat = $e:expr) => {test!(($p,$e))}; | -- this is interpreted as pattern `1 + 1` (in expansion #2) ... LL | (($p:pat, $e:pat)) => {let $p = $e;}; | ^^ expected expression ... LL | test!(let x = 1+1); | ------------------ | | | | | this is interpreted as expression `1 + 1` (in expansion #1) | in this macro invocation | = note: this error originates in the macro `test` (in Nightly builds, run with -Z macro-backtrace for more info) ```
estebank
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Oct 15, 2023
…ment Partially address rust-lang#71039.
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Nov 16, 2023
…ment Partially address rust-lang#71039.
estebank
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Nov 16, 2023
…ment Partially address rust-lang#71039.
bors
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Nov 16, 2023
More detail when expecting expression but encountering bad macro argument Partially address rust-lang#71039. ``` error: expected expression, found pattern `1 + 1` --> $DIR/trace_faulty_macros.rs:49:37 | LL | (let $p:pat = $e:expr) => {test!(($p,$e))}; | ------- -- this is interpreted as expression, but it is expected to be pattern | | | this macro fragment matcher is expression ... LL | (($p:pat, $e:pat)) => {let $p = $e;}; | ------ ^^ expected expression | | | this macro fragment matcher is pattern ... LL | test!(let x = 1+1); | ------------------ | | | | | this is expected to be expression | in this macro invocation | = note: when forwarding a matched fragment to another macro-by-example, matchers in the second macro will see an opaque AST of the fragment type, not the underlying tokens = note: this error originates in the macro `test` (in Nightly builds, run with -Z macro-backtrace for more info) ```
nnethercote
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Jun 27, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
nnethercote
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Jun 28, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
nnethercote
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Jul 8, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
nnethercote
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Jul 19, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
nnethercote
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Jul 22, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
nnethercote
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Aug 5, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
nnethercote
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Sep 10, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
compiler-errors
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Sep 14, 2024
The one notable test change is `tests/ui/macros/trace_faulty_macros.rs`. This commit removes the complicated `Interpolated` handling in `expected_expression_found` that results in a longer error message. But I think the new, shorter message is actually an improvement. The original complaint was in rust-lang#71039, when the error message started with "error: expected expression, found `1 + 1`". That was confusing because `1 + 1` is an expression. Other than that, the reporter said "the whole error message is not too bad if you ignore the first line". Subsequently, extra complexity and wording was added to the error message. But I don't think the extra wording actually helps all that much. In particular, it still says of the `1+1` that "this is expected to be expression". This repeats the problem from the original complaint! This commit removes the extra complexity, reverting to a simpler error message. This is primarily because the traversal a pain without `Interpolated` tokens. Nonetheless, I think the error message is *improved*. It now starts with "expected expression, found `pat` metavariable", which is much clearer and the real problem. It also doesn't say anything specific about `1+1`, which is good, because the `1+1` isn't really relevant to the error -- it's the `$e:pat` that's important.
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I’ll admit, the whole error message is not too bad if you ignore the first line.
If only it wouldn’t suggest that
1 + 1is not an expression...(Playground)
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@rustbot modify labels to T-compiler, A-macros, C-enhancement, D-papercut, A-diagnostics
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