☂️ Syntax errors raised by the compiler

[dhruvmanila]

This is an umbrella issue to collect all the syntax errors that are raised by the CPython compiler. These are different than the ones that are raised by the parser. IOW, the source code which raises these errors are valid as per the grammar.

• Duplicate parameter names ([syntax-errors] Make duplicate parameter names a semantic error #17131)
• await outside async function (PLE1142) ([syntax-errors] await outside async functions #17363)
• yield outside function (F704) ([syntax-errors] yield, yield from, and await outside functions #17298)
• return outside function (F706) ([syntax-errors] return outside function #17300)
• await in annotations (extending the yield and named expression handling from [syntax-errors] Invalid syntax in annotations #17101) ([syntax-errors] Extend annotation checks to await #17282)
• PEP 649 annotations in annotated assignments ([syntax-errors] Check annotations in annotated assignments #17283)
• Ruff fails to reject invalid syntax in annotation scopes #11118 ([syntax-errors] Invalid syntax in annotations #17101)
  • PEP 649
• Duplicate key in mapping match pattern (case {"x": 1, "x": 2}:) ([syntax-errors] Detect duplicate keys in match mapping patterns #17129)
• Name assigned before global declaration (PLE0118) ([syntax-errors] Reimplement PLE0118 #17135)
• Flag starred expressions in return and yield #16520 ([syntax-errors] Starred expressions in return, yield, and for #17134)
• Ruff doesn't raise syntax error for single starred assignment target #13759 (cpython#100581)
• Multiple assignments to name 'a' in pattern (case [a, b, a]:)
• Irrefutable patterns are syntax errors
  • SyntaxError: name capture 'x' makes remaining patterns unreachable
  • SyntaxError: wildcard makes remaining patterns unreachable
• Ruff fails to detect duplicate type parameter names #11119
• No syntax error for [(a := ...) for a in b] #14395

A lot of them are mentioned in this comment. These all would be part of E999 rule.

Version-related errors

The following are both version-related and detected by the compiler. Many of them were originally tracked in #6591.

3.13

• global declarations in try nodes (cpython#111123) ([syntax-errors] Document behavior of global declarations in try nodes before 3.13 #17285)
  • Are now allowed in except blocks if the variable is only referenced in an else block
  • Are now disallowed in else blocks if the variable is only referenced in an except block

3.11

• Async comprehensions are now allowed when nested inside sync comprehensions in async functions (cpython#77527) ([syntax-errors] Async comprehension in sync comprehension #17177)

3.10

• del __debug__ is a syntax error on Python 3.10+ (cpython#89163)