improve error message when two-arg assert_eq! receives a trailing comma #39554
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r? @BurntSushi (rust_highfive has picked a reviewer for you, use r? to override) |
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@zackmdavis Thanks! Is there a way to write a compile-fail test for this? |
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This would be a UI test, I imagine (see the |
Previously, `assert_eq!(left, right,)` (respectively, `assert_ne!(left, right,)`; note the trailing comma) would result in a confusing "requires at least a format string argument" error. In reality, a format string is optional, but the trailing comma puts us into the "match a token tree of zero or more tokens" branch of the macro (in order to support the optional format string), and passing the empty token tree into `format_args!` results in the confusing error. If instead we match a token tree of one or more tokens, we get a much more sensible "unexpected end of macro invocation" error. While we're here, fix up a stray space before a comma in the match guards. Resolves rust-lang#39369.
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@BurntSushi ping? |
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@bors r+ |
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📌 Commit 65435e1 has been approved by |
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@zackmdavis Sorry about that! Thank you! :-) |
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…age_when_given_a_trailing_comma, r=BurntSushi improve error message when two-arg assert_eq! receives a trailing comma Previously, `assert_eq!(left, right,)` (respectively, `assert_ne!(left, right,)`; note the trailing comma) would result in a confusing "requires at least a format string argument" error. In reality, a format string is optional, but the trailing comma puts us into the "match a token tree of zero or more tokens" branch of the macro (in order to support the optional format string), and passing the empty token tree into `format_args!` results in the confusing error. If instead we match a token tree of one or more tokens, we get a much more sensible "unexpected end of macro invocation" error. While we're here, fix up a stray space before a comma in the match guards. Resolves #39369. ----- **Before:** ``` $ rustc scratch.rs error: requires at least a format string argument --> scratch.rs:2:5 | 2 | assert_eq!(1, 2,); | ^^^^^^^^^^^^^^^^^^ | = note: this error originates in a macro outside of the current crate error: aborting due to previous error ``` **After:** ``` $ ./build/x86_64-unknown-linux-gnu/stage1/bin/rustc scratch.rs error: unexpected end of macro invocation --> scratch.rs:2:20 | 2 | assert_eq!(1, 2,); | ^ ```
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☀️ Test successful - status-appveyor, status-travis |
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Previously,
assert_eq!(left, right,)(respectively,assert_ne!(left, right,); note the trailing comma) would result in a confusing "requiresat least a format string argument" error. In reality, a format string is
optional, but the trailing comma puts us into the "match a token tree of
zero or more tokens" branch of the macro (in order to support the
optional format string), and passing the empty token tree into
format_args!results in the confusing error. If instead we match atoken tree of one or more tokens, we get a much more sensible
"unexpected end of macro invocation" error.
While we're here, fix up a stray space before a comma in the match
guards.
Resolves #39369.
Before:
After: