Description
Description
New Swift programmers with a C-like language background or polyglot programmers often find themselves mistakenly using the C-style parameter declaration, e.g.
func cStyle(X x) {}Currently there's a diagnostic emitted for this case:
DiagnosticSpec(message: "expected ':' in parameter", fixIts: ["insert ':'"])Undeniably this is the most unsurprising diagnostic for anyone except for the beginners.
Notwithstanding, when the type is structural,
func cStyleWithStructuralType(Array.Index i) {}As structural types such as Array.Index cannot be identifiers, the parser should not recognize Array.Index as an identifier. However, the diagnostics currently emitted are suboptimal,
DiagnosticSpec(message: "expected ':' and type in parameter", fixIts: ["insert ':'"])
DiagnosticSpec(message: "unexpected code '.Index i' in parameter clause")Applying the fix-it "insert ':'" will result in an undesirable outcome,
func cStyleWithStructuralType(Array: <#type#>.Index i)This issue is also applicable to closure parameters and enum case parameters,
let cStyleWithStructuralType = { (Array.Index i) in }
case cStyleWithStructuralType(Array.Index i)We should improve diagnostics for the situations above by emitting diagnostics like these,
DiagnosticSpec(message: "expected ':' in parameter", fixIts: ["insert ':'"])
DiagnosticSpec(message: "'i' must precede 'Array.Index'", fixIts: ["move 'i' in front of 'Array.Index'"])