Warn when a function name starts with a capital letter

[timfennis]

Struct names are conventionally capitalized and their constructors are ordinary function bindings (#197). A user-defined fn with a capitalized name can therefore collide with — or masquerade as — a constructor. Found while reviewing #197:

fn Point(x) { "the function" }
struct Point { x: Int }
print(Point("str"));  // "the function"
print(Point(1));      // Point {x: 1}

This is silently accepted (the two become type-dispatched overloads), while the reverse order — struct Point first, then fn Point(x) — errors with Illegal redefinition of function 'Point' with 1 parameter.

Proposal

Emit an analyser warning when a user-defined fn (named or via let) has a name starting with a capital letter, steering capitalized names toward struct constructors. Struct constructors themselves are of course exempt.

Open questions

• The language has no warning channel yet — analysis errors are fatal. Does this need warning infrastructure first (also useful elsewhere, e.g. unused variables), or should this specific case be an error?
• Should the asymmetry above also be fixed, so fn + struct collisions are rejected consistently in both orders?

🤖