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Zack M. Davis
1f04597c3c
Programmers used to working in some other languages (such as Python or Go) might expect to be able to destructure values with comma-separated identifiers but no parentheses on the left side of an assignment. Previously, the first name in such code would get parsed as a single-indentifier pattern—recognizing, for example, the `let a` in `let a, b = (1, 2);`—whereupon we would have a fatal syntax error on seeing an unexpected comma rather than the expected semicolon (all the way nearer to the end of `parse_full_stmt`). Instead, let's look for that comma when parsing the pattern, and if we see it, momentarily make-believe that we're parsing the remaining elements in a tuple pattern, so that we can suggest wrapping it all in parentheses. We need to do this in a separate wrapper method called on the top-level pattern (or `|`-patterns) in a `let` statement, `for` loop, `if`- or `while let` expression, or match arm rather than within `parse_pat` itself, because `parse_pat` gets called recursively to parse the sub-patterns within a tuple pattern. Resolves #48492.
NB: This crate is part of the Rust compiler. For an overview of the
compiler as a whole, see
the README.md file found in librustc.
The syntax crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.