Comprehensively support trailing commas in std/core macros
I carefully organized the changes into four commits:
* Test cases
* Fixes for `macro_rules!` macros
* Fixes for builtin macros
* Docs for builtins
**I can easily scale this back to just the first two commits for now if such is desired.**
### Breaking (?) changes
* This fixes#48042, which is a breaking change that I hope people can agree is just a bugfix for an extremely dark corner case.
* To fix five of the builtins, this changes `syntax::ext::base::get_single_str_from_tts` to accept a trailing comma, and revises the documentation so that this aspect is not surprising. **I made this change under the (hopefully correct) understanding that `libsyntax` is private rustc implementation detail.** After reviewing all call sites (which were, you guessed it, *precisely those five macros*), I believe the revised semantics are closer to the intended spirit of the function.
### Changes which may require concensus
Up until now, it could be argued that some or all the following macros did not conceptually take a comma-separated list, because they only took one argument:
* **`cfg(unix,)`** (most notable since cfg! is unique in taking a meta tag)
* **`include{,_bytes,_str}("file.rs",)`** (in item form this might be written as "`include!{"file.rs",}`" which is even slightly more odd)
* **`compile_error("message",);`**
* **`option_env!("PATH",)`**
* **`try!(Ok(()),)`**
So I think these particular changes may require some sort of consensus. **All of the fixes for builtins are included this list, so if we want to defer these decisions to later then I can scale this PR back to just the first two commits.**
### Other notes/general requests for comment
* Do we have a big checklist somewhere of "things to do when adding macros?" My hope is for `run-pass/macro-comma-support.rs` to remain comprehensive.
* Originally I wanted the tests to also comprehensively forbid double trailing commas. However, this didn't work out too well: [see this gist and the giant FIXME in it](https://gist.github.com/ExpHP/6fc40e82f3d73267c4e590a9a94966f1#file-compile-fail_macro-comma-support-rs-L33-L50)
* I did not touch `select!`. It appears to me to be a complete mess, and its trailing comma mishaps are only the tip of the iceberg.
* There are [some compile-fail test cases](https://github.com/ExpHP/rust/blob/5fa97c35da2f0ee/src/test/compile-fail/macro-comma-behavior.rs#L49-L52) that didn't seem to work (rustc emits errors, but compile-fail doesn't acknowledge them), so they are disabled. Any clues? (Possibly related: These happen to be precisely the set of errors which are tagged by rustc as "this error originates in a macro outside of the current crate".)
---
Fixes#48042Closes#46241
Most notably this changes 'syntax::ext::base::get_single_str_from_tts'
to accept a trailing comma, and revises the documentation so that this
aspect is not surprising. I made this change under the understanding
that this crate is private rustc implementation detail (I hope this is
correct!). After reviewing all call sites, I believe the revised
semantics are closer to the intended spirit of the function.
Run rustfmt and add doc comments to libsyntax/ext/tt/macro_parser.rs
Similar to #47603
cc @theotherphil since you reviewed my other PR 😄
And because they are already assigned on #47603:
r? @arielb1
Run rustfmt and add doc comments to libsyntax/ext/tt/quoted.rs
I was already going to try to understand this code to try to implement rust-lang/rfcs#2298. I figured I would put that knowledge into comments and share... This PR contains _no changes_ to the code itself -- just formatting and comments.
I'm not sure what the best way to do this is. I plan to make more such PR for other files, but I figured it would have fewer conflicts if I do it file by file...
Point at unused arguments for format string
Avoid overlapping spans by only pointing at the arguments that are not
being used in the argument string. Enable libsyntax to have diagnostics
with multiple primary spans by accepting `Into<MultiSpan>` instead of
`Span`.
Partially addresses #41850.
Avoid overlapping spans by only pointing at the arguments that are not
being used in the argument string. Enable libsyntax to have diagnostics
with multiple primary spans by accepting `Into<MultiSpan>` instead of
`Span`.
Started rebasing @sgrif's PR #33135 off of current master. (Well, actually merging it into a new branch based off current master.)
The following files still need to be fixed or at least reviewed:
- `src/libsyntax/ext/tt/macro_parser.rs`: calls `Parser::parse_lifetime`, which doesn't exist anymore
- `src/libsyntax/parse/parser.rs`: @sgrif added an error message to `Parser::parse_lifetime`. Code has since been refactored, so I just took it out for now.
- `src/libsyntax/ext/tt/transcribe.rs`: This code has been refactored bigtime. Not sure whether @sgrif's changes here are still necessary. Took it out for this commit.
Do not expand a derive invocation when derive is not allowed
Closes#46655.
The first commit is what actually closes#46655. The second one is just a refactoring I have done while waiting on a test.
1. Change the return type of `expand_invoc()` and its subroutines to
`Option<Expansion>` from `Expansion`.
2. Return `None` when expanding a derive invocation if the item cannot
have derive on it (in `expand_derive_invoc()`).
Do not emit type errors on recovered blocks
When a parse error occurs on a block, the parser will recover and create
a block with the statements collected until that point. Now a flag
stating that a recovery has been performed in this block is propagated
so that the type checker knows that the type of the block (which will be
identified as `()`) shouldn't be checked against the expectation to
reduce the amount of irrelevant diagnostic errors shown to the user.
Fix#44579.
bors