When parsing a pattern, if we encounter something that isn't pattern
syntax, try parsing as an expression instead. We only need one-token
lookahead to distinguish pattern syntax from expression syntax.
Track a precedence group through pattern parsing so that we can allow
different kinds of expressions in a top-level pattern (such as the
operand of `let`) and in a nested pattern (such as a subpattern of a
tuple pattern or within grouping parens). For example, we do not allow
`case if ...`, and for now I've chosen to also not allow logical or
relational operators at the top level of a pattern, so `case 1 + 1` is
OK, but `case 1 == 1` and `case true and false` require parentheses.
This decision should be ratified or revisited by a design proposal.
Very basic check support is also provided, only sufficient to form an
`ExprPattern` instruction and nothing beyond that. For now, all pattern
matching against an `ExprPattern` fails with a TODO error. To support
that, I've switched from calling `BeginSubpattern` in the parent handler
of a pattern and `EndSubpatternAs*` in the pattern handler itself to
calling both functions in parent handlers, with `EndSubpattern`
converting an expression into an expression pattern where needed.
Depends on #6976.
Assisted-by: Gemini via Google Antigravity
Echoing what was added in #5608, updating existing uses. Unfortunately
there's divergent behavior for operators versus constructors, so keeping
the nolint on those.
Includes support for the `impls`, `=`, and `==` requirement operators to
the right of a `where`, but `and` to allow multiple requirements is
still a TODO.
---------
Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Per [#toolchain
discussion](https://discord.com/channels/655572317891461132/655578254970716160/1176632520834560211)
We'd at one point been trying to put `[[nodiscard]]` everywhere, but
then we stopped because it had felt verbose without finding many issues
(plus, people plain forgot to add it). Some history in #888.
Since newer code gets added without it, we now have code like:
```
auto GetLineInfo(Line line) -> LineInfo&;
[[nodiscard]] auto GetLineInfo(Line line) const -> const LineInfo&;
auto AddLine(LineInfo info) -> Line;
auto GetTokenInfo(Token token) -> TokenInfo&;
[[nodiscard]] auto GetTokenInfo(Token token) const -> const TokenInfo&;
auto AddToken(TokenInfo info) -> Token;
[[nodiscard]] auto GetTokenPrintWidths(Token token) const -> PrintWidths;
```
Here, the lack of `[[nodiscard]]` doesn't mean anything: for example,
`GetLineInfo` should not have its result discarded if it's called. But
the mix could be confusing for readers.
As a resolution, remove the attribute. `[[nodiscard]]` should be treated
like other attributes going forward, which essentially means "avoid in
general, add a comment to explain why the attribute is needed" rather
than use-as-default.
Continuing with #3070. Just a dir and file rename (only prefix change is
lexer_file_test). Everything in the lex dir should be marked as a move.
Note, I think this closes#3070. There may still be further cleanup
later, but the organizational changes suggested there are being
completed.
---------
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
Continuing with #3070. Just a dir and file rename (mostly removing
prefixes, although for parse_tree_fuzzer and parse_tree_file_test I'm
dropping "tree" instead of "parse"). Everything in the parse dir should
be marked as a move.
Richard Smith
Özgür
Geoff Romerandjosh11b
Dana Jansens
Jon Ross-Perkins
Chandler Carruth
