Confusing error message if you forget the width of the * format specifier #49384
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A-diagnostics
Area: Messages for errors, warnings, and lints
C-enhancement
Category: An issue proposing an enhancement or a PR with one.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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Centril
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Aug 2, 2019
…hton
On `format!()` arg count mismatch provide extra info
When positional width and precision formatting flags are present in a
formatting string that has an argument count mismatch, provide extra
information pointing at them making it easiser to understand where the
problem may lay:
```
error: 4 positional arguments in format string, but there are 3 arguments
--> $DIR/ifmt-bad-arg.rs:78:15
|
LL | println!("{} {:.*} {}", 1, 3.2, 4);
| ^^ ^^--^ ^^ --- this parameter corresponds to the precision flag
| |
| this precision flag adds an extra required argument at position 1, which is why there are 4 arguments expected
|
= note: positional arguments are zero-based
= note: for information about formatting flags, visit https://doc.rust-lang.org/std/fmt/index.html
error: 4 positional arguments in format string, but there are 3 arguments
--> $DIR/ifmt-bad-arg.rs:81:15
|
LL | println!("{} {:07$.*} {}", 1, 3.2, 4);
| ^^ ^^-----^ ^^ --- this parameter corresponds to the precision flag
| | |
| | this precision flag adds an extra required argument at position 1, which is why there are 4 arguments expected
| this width flag expects an `usize` argument at position 7, but there are 3 arguments
|
= note: positional arguments are zero-based
= note: for information about formatting flags, visit https://doc.rust-lang.org/std/fmt/index.html
error: invalid reference to positional argument 7 (there are 3 arguments)
--> $DIR/ifmt-bad-arg.rs:84:18
|
LL | println!("{} {:07$} {}", 1, 3.2, 4);
| ^^^--^
| |
| this width flag expects an `usize` argument at position 7, but there are 3 arguments
|
= note: positional arguments are zero-based
= note: for information about formatting flags, visit https://doc.rust-lang.org/std/fmt/index.html
```
Fix rust-lang#49384.
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Playground link: https://play.rust-lang.org/?gist=fea3e7d4c4151751bb66b69ba906ea88&version=stable
If the
*formatting specifier is used, it expects an additional argument. But it does not account for this when printing an error message, so in the above example where an argument was forgotten, the error is "error: 1 positional argument in format string, but there is 1 argument". It should indicate that there are in fact 2 positional arguments in the format string, due to*.The text was updated successfully, but these errors were encountered: