This is a work in progress PR that potentially should fix#29084, #28308, #25385, #28288, #31011. I think this may also adresse parts of #2887.
The problem in this issues seems to be that when transcribing macro arguments, we just clone the argument Nonterminal, which still has to original spans. This leads to the unprintable spans. One solution would be to update the spans of the inserted argument to match the argument in the macro definition. So for [this testcase](https://github.com/rust-lang/rust/compare/master...fhahn:macro-ice?expand=1#diff-f7def7420c51621640707b6337726876R2) the error message would be displayed in the macro definition:
src/test/compile-fail/issue-31011.rs:4:12: 4:22 error: attempted access of field `trace` on type `&T`, but no field with that name was found
src/test/compile-fail/issue-31011.rs:4 if $ctx.trace {
Currently I've added a very simple `update_span` function, which updates the span of the outer-most expression of a `NtExpr`, but this `update_span` function should be updated to handle all Nonterminals. But I'm pretty new to the macro system and would like to check if this approach makes sense, before doing that.
This is achieved by adding the scan_back method. This method looks back
through the source_text of the StringReader until it finds the target
char, returning it's offset in the source. We use this method to find
the offset of the opening single quote, and use that offset as the start
of the error.
Given this code:
```rust
fn main() {
let _ = 'abcd';
}
```
The compiler would give a message like:
```
error: character literal may only contain one codepoint: ';
let _ = 'abcd';
^~
```
With this change, the message now displays:
```
error: character literal may only contain one codepoint: 'abcd';
let _ = 'abcd';
^~~~~~~
```
Fixes#30033
[breaking-change]
syntax::errors::Handler::new has been renamed to with_tty_emitter
Many functions which used to take a syntax::errors::ColorConfig, now take a rustc::session::config::ErrorOutputType. If you previously used ColorConfig::Auto as a default, you should now use ErrorOutputType::default().
Given this code:
fn main() {
let _ = 'abcd';
}
The compiler would give a message like:
error: character literal may only contain one codepoint: ';
let _ = 'abcd';
^~
With this change, the message now displays:
error: character literal may only contain one codepoint: 'abcd'
let _ = 'abcd'
^~~~~~
Fixes#30033
This PR fixes an ICE due to an DiagnosticsBuilder not being canceld or emitted.
Ideally it would use `Handler::cancel`, but I did not manage to get a `&mut` reference to the diagnostics handler.
The motivation (other than removing boilerplate) is that this is a baby step towards a parser with error recovery.
[breaking-change] if you use any of the changed functions, you'll need to remove a try! or panictry!
The current help message is too much about "normal" macros to be used
as general message. Keep it for normal macros, and add custom help and
error messages for macro definitions.
The current help message is too much about "normal" macros to be used
as general message. Keep it for normal macros, and add custom help and
error messages for macro definitions.
This PR is a rebase of the original PR by @eddyb https://github.com/rust-lang/rust/pull/21836 with some unrebasable parts manually reapplied, feature gate added + type equality restriction added as described below.
This implementation is partial because the type equality restriction is applied to all type ascription expressions and not only those in lvalue contexts. Thus, all difficulties with detection of these contexts and translation of coercions having effect in runtime are avoided.
So, you can't write things with coercions like `let slice = &[1, 2, 3]: &[u8];`. It obviously makes type ascription less useful than it should be, but it's still much more useful than not having type ascription at all.
In particular, things like `let v = something.iter().collect(): Vec<_>;` and `let u = t.into(): U;` work as expected and I'm pretty happy with these improvements alone.
Part of https://github.com/rust-lang/rust/issues/23416
