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Rollup merge of #124488 - est31:arbitrary_expressions_error, r=pnkfelix
Add a note to the ArbitraryExpressionInPattern error The current "arbitrary expressions aren't allowed in patterns" error is confusing, as it fires for code where it *looks* like a pattern but the compiler still treats it as an expression. That this is due to the `:expr` fragment specifier forcing the expression-ness property on the code. In the test suite, the "arbitrary expressions aren't allowed in patterns" error can only be found in combination with macro_rules macros that force expression-ness of their content, namely via `:expr` metavariables. I also can't come up with cases where there would be an expression instead of a pattern, so I think it's always coming from an `:expr`. In order to make the error less confusing, this adds a note explaining the weird `:expr` fragment behaviour. Fixes #99380
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,11 @@ | ||
macro_rules! foo { | ||
($p:expr) => { | ||
if let $p = Some(42) { | ||
return; | ||
} | ||
}; | ||
} | ||
|
||
fn main() { | ||
foo!(Some(3)); //~ ERROR arbitrary expressions aren't allowed in patterns | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,10 @@ | ||
error: arbitrary expressions aren't allowed in patterns | ||
--> $DIR/expr-in-pat-issue-99380.rs:10:10 | ||
| | ||
LL | foo!(Some(3)); | ||
| ^^^^^^^ | ||
| | ||
= note: the `expr` fragment specifier forces the metavariable's content to be an expression | ||
|
||
error: aborting due to 1 previous error | ||
|
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