Refinement on the message for CS0103, or a new rule.

[otac0n]

Analyzer

Diagnostic ID: CS0103

Describe the improvement

• Given a CS0103 where the syntax => is available (e.g. replace x = x.foo with x => x.foo) (for one case but maybe more, with wider closure exceptions)
  • If the assignment is from an object reference's closure to the object reference (any expression on x that assigns to x but does not close over additional variables) (Consider that the assignment may be a typo for a lambda.)
    • Evaluate the replaced lambda (syntactically and async semantically?).
    • If replaced expression is valid (e.g. replace x = x.foo with x => x.foo)
      • Augment the CS0103 with a new warning to check for a typo of '=' vs '=>'

Describe suggestions on how to achieve the rule

As above, replace the syntax tree. If the parse is better (according to constrained analysis), update the existing diagnostic.

Additional context

.Select(x => x.word)

vs

.Select(x = x.word)

[otac0n]

These are all bad suggestions.

[huoyaoyuan]

x = x.word is a perfectly valid expression to be passed as an argument if x is an identifier.

[otac0n]

Yes, I'm aware. But in the case that this is a raised semantic error, I would prefer the message to be improved.