Add help message for missing `IndexMut` impl
Code:
```rust
let mut map = HashMap::new();
map.insert("peter", 23);
map["peter"] = 27;
```
Before:
```
error[E0594]: cannot assign to immutable indexed content
--> src/main.rs:7:5
|
7 | map["peter"] = 27;
| ^^^^^^^^^^^^^^^^^ cannot borrow as mutable
```
With this change (just the `help` was added):
```
error[E0594]: cannot assign to immutable indexed content
--> index-error.rs:7:5
|
7 | map["peter"] = 27;
| ^^^^^^^^^^^^^^^^^ cannot borrow as mutable
|
= help: trait `IndexMut` is required to modify indexed content, but it is not implemented for std::collections::HashMap<&str, i32>
```
---
Yesterday I did some pair programming with a Rust-beginner. We created a type and implemented `Index` for it. Trying to modify the value returned by the index operation returns in a rather vague error that was not very clear for the Rust beginner. So I tried to improve the situation.
## Notes/questions for reviewers:
- Is the formulation OK like that? I'm fine with changing it.
- Can we be absolutely sure that `IndexMut` is actually not implemented in the case my `help` message is added? I'm fairly sure myself, but there could be some cases I didn't think of. Also, I don't know the compiler very well, so I don't know what exactly certain enum variants are used for.
- It would be nice to test if `IndexMut` is in fact not implemented for the type, but I couldn't figure out how to check that. If you think that additional check would be beneficial, could you tell me how to check if a trait is implemented?
- Do you think I should change the error message instead of only adding an additional help message?
Rollup of 15 pull requests
Successful merges:
- #52773 (Avoid unnecessary pattern matching against Option and Result)
- #53082 (Fix doc link (again))
- #53094 (Automatically expand section if url id point to one of its component)
- #53106 (atomic ordering docs)
- #53110 (Account for --remap-path-prefix in save-analysis)
- #53116 (NetBSD: fix signedess of char)
- #53179 (Whitelist wasm32 simd128 target feature)
- #53183 (Suggest comma when missing in macro call)
- #53207 (Add individual docs for rotate_{left, right})
- #53211 ([nll] enable feature(nll) on various crates for bootstrap)
- #53214 ([nll] enable feature(nll) on various crates for bootstrap: part 2)
- #53215 (Slightly refactor syntax_ext/format)
- #53217 (inline some short functions)
- #53219 ([nll] enable feature(nll) on various crates for bootstrap: part 3)
- #53222 (A few cleanups for rustc_target)
A few cleanups for rustc_target
- remove redundant struct field names
- shorten a self-assignment
- prefer `unwrap_or_else` in case of function calls
- collapse an `if`
- collapse a double `map()`
- match on dereferenced objects
- consume `self` if it implements `Copy`
Slightly refactor syntax_ext/format
expand_preparsed_format_args:
- move a potential error `return` earlier in the processing
- pre-allocate some of the required space for `cx.pieces` and `cx.str_pieces`
- create `cx`-independent objects before `cx`
- build `pieces` and `errs` using `collect` instead of a `push` loop
describe_num_args:
- return `Cow<str>` instead of `String`
Suggest comma when missing in macro call
When missing a comma in a macro call, suggest it, regardless of
position. When a macro call doesn't match any of the patterns, check
if the call's token stream could be missing a comma between two idents,
and if so, create a new token stream containing the comma and try to
match against the macro patterns. If successful, emit the suggestion.
This works on arbitrary macros, with no need of special support from
the macro writers.
```
error: no rules expected the token `d`
--> $DIR/missing-comma.rs:26:18
|
LL | foo!(a, b, c d, e);
| -^
| |
| help: missing comma here
```
Follow up to #52397.
Apply some fixes to cross-language LTO (especially when targeting MSVC)
This PR contains a few fixes that were needed in order to get Firefox compiling with Rust/C++ cross-language ThinLTO on Windows. The commits are self-contained and should be self-explanatory.
r? @alexcrichton
Account for --remap-path-prefix in save-analysis
Fixes#52549.
Didn't add a test since save-analysis is still unstable, only tested this locally. Should I add a test for that? If so, is run-make-fulldeps an appropriate format?
Session is already created with remapped working directory, so use that instead of the actual cwd.
This was the only place affected, since the rest of the paths in save-analysis are directly derived from files in spans from `sess.codemap()`, which already creates remapped ones.
r? @nrc
clarify partially initialized Mutex issues
Using a `sys_common::mutex::Mutex` without calling `init` is dangerous, and yet there are some places that do this. I tried to find all of them and add an appropriate comment about reentrancy.
I found two places where (I think) reentrancy can actually occur, and was not able to come up with an argument for why this is okay. Someone who knows `io::lazy` and/or `sys_common::at_exit_imp` should have a careful look at this.
