assert_eq failure message easier to read
By having the left and right strings aligned with one another it helps spot the difference between the two far quicker than if they are on the same line.
E.g.
Before:
```
thread 'tests::test_safe_filename' panicked at 'assertion failed: `(left == right)` left: `"-aandb--S123.html"` right: `"-aandb-S123.html"`',
```
After:
```
thread 'tests::test_safe_filename' panicked at 'assertion failed: `(left == right)`
left: `"-aandb--S123.html"`
right: `"-aandb-S123.html"`',
```
When the strings are both on the same line it take a lot longer to spot the difference. It is a small change but the small time savings add up with repetition. This would help Rust be an excellent language to write tests in out of the box.
Closes https://github.com/rust-lang/rust/issues/41615
core: allow messages in unimplemented!() macro
This makes `unimplemented!()` match `unreachable!()`, allowing a message and possible formatting to be provided to better explain what and/or why something is not implemented.
I've used this myself in hyper for a while, include the type and method name, to better help while prototyping new modules, like `unimplemented!("Conn::poll_complete")`, or `unimplemented!("Conn::poll; state={:?}", state)`.
By having the left and right strings above and below on the same line it helps spot the difference between the two. E.g.
thread 'tests::test_safe_filename' panicked at 'assertion failed: `(left == right)`
left: `"-aandb--S123.html"`
right: `"-aandb-S123.html"`',
When the strings are both on the same line it take a lot longer to spot the difference. It is a small change but the small time savings add up with repetition. This helps Rust be an excellent language to write tests in.
This change reduces duplication by linking the documentation for
`writeln!` to `write!`. It also restructures the `write!` documentation
to read in a more logical manner.
Updates #29329, #29381
Previously, `assert_eq!(left, right,)` (respectively, `assert_ne!(left,
right,)`; note the trailing comma) would result in a confusing "requires
at least a format string argument" error. In reality, a format string is
optional, but the trailing comma puts us into the "match a token tree of
zero or more tokens" branch of the macro (in order to support the
optional format string), and passing the empty token tree into
`format_args!` results in the confusing error. If instead we match a
token tree of one or more tokens, we get a much more sensible
"unexpected end of macro invocation" error.
While we're here, fix up a stray space before a comma in the match
guards.
Resolves#39369.
Document convention for using both fmt::Write and io::Write
Using a trait's methods (like `Write::write_fmt` as used in `writeln!` and other macros) requires importing that trait directly (not just the module containing it). Both `fmt::Write` and `io::Write` provide compatible `Write::write_fmt` methods, and code can use `writeln!` and other macros on both an object implementing `fmt::Write` (such as a `String`) and an object implementing `io::Write` (such as `Stderr`). However, importing both `Write` traits produces an error due to the name conflict.
The convention I've seen renames both of them on import, to `FmtWrite` and `IoWrite` respectively. Document that convention in the Rust documentation for `write!` and `writeln!`, with examples.
Copyediting on documentation for write! and writeln!
Fix various sentence fragments, missing articles, and other grammatical issues in the documentation for write! and writeln!.
Also fix the links (and link names) for common return types.
(Noticed when preparing https://github.com/rust-lang/rust/pull/37472 ; posted separately to avoid mixing the new documentation with copyedits to existing documentation.)
Fix various sentence fragments, missing articles, and other grammatical
issues in the documentation for write! and writeln!.
Also fix the links (and link names) for common return types.
Removes the `STATUSES` static which duplicates truth from the pattern
match in `collect_lang_features`.
Fixes existing duplicates by renaming:
- never_type{,_impls} on `impl`s on `!`
- concat_idents{,_macro} on `macro_rules! concat_idents`
Fixes#37013.
