Improve diagnostics for misspelt 'assocatedtype'

[karwa]

Description

Almost everything in Swift uses camelCase. A notable exception is associatedtype. If a user happens to write associatedType in a protocol declaration we currently provide rather poor diagnostics, assuming they meant to declare a function requirement. We should improve those diagnostics, pointing them to the recognised spelling.

Steps to reproduce

Welcome to Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100).
Type :help for assistance.
  1> protocol A { 
  2.     associatedType Foo 
  3. }
expression failed to parse:
error: error while processing module import: error: repl.swift:2:5: error: expected 'func' keyword in instance method declaration
    associatedType Foo
    ^
    func 

error: repl.swift:2:20: error: found an unexpected second identifier in function declaration; is there an accidental break?
    associatedType Foo
                   ^

repl.swift:2:20: note: join the identifiers together
    associatedType Foo
    ~~~~~~~~~~~~~~~^~~
    associatedTypeFoo

error: repl.swift:2:23: error: expected '(' in argument list of function declaration
    associatedType Foo
                      ^



fixed expression suggested:
  protocol A {
    associatedType Foo
}

Note that the suggested "fixed" expression does not correct the capitalisation.

Expected behavior

Expect we would notice that a user writing associatedType is clearly trying to write associatedtype, and direct them to the correct spelling.

Environment

• Swift compiler version info

swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
Target: arm64-apple-macosx13.0

• Xcode version info

Xcode 14.3
Build version 14E222b

[AnthonyLatsis]

@ahoppen Should we start transferring parser recovery issues like these to swift-syntax?

[ahoppen]

Yes, we should track them in the swift-syntax repo + attach the SwiftParser keyword.

[ahoppen]

Tracked in Apple’s issue tracker as rdar://115385848

[AnthonyLatsis]

Yes, we should track them in the swift-syntax repo

Here are some more: #2196, #2204, #2198.