Previously when breaking tokens into smaller pieces, the replace_token
function have been used. It replaced current token and updated span
information, but it did not clear the list of expected tokens, neither
did it update remaining info about last token. This could lead to
incorrect error message, like one described in the issue #24780:
expected one of ... `>` ... found `>`
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.
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
