Variables named `ref` cannot be used with method calls

[volsa]

Variables named ref cannot be used with method calls

Description

A local variable named ref (case-insensitive) fails to resolve method calls. The compiler's resolver incorrectly binds ref to the REF builtin function instead of the local variable when processing call operators, causing "Could not resolve reference" errors on any subsequent member access.

Minimal Reproduction

FUNCTION_BLOCK MyFb
    METHOD foo
        printf('MyFb::foo$N');
    END_METHOD
END_FUNCTION_BLOCK

FUNCTION main
    VAR
        ref: MyFb;
    END_VAR

    ref.foo();
END_FUNCTION

Expected Output

MyFb::foo

Actual Output

error[E048]: Could not resolve reference to foo
   ┌─ test.st:12:9
   │
12 │     ref.foo();
   │         ^^^ Could not resolve reference to foo

Root Cause

REF is registered as a builtin function in src/builtins.rs. When the resolver processes a call statement like ref.foo(), it resolves the operator using call_operator_scopes, which is ordered as [FunctionsOnly, Variable, POU, DataType]. Since FunctionsOnly runs first and matches the REF builtin (case-insensitive), the resolver annotates ref as Function { qualified_name: "REF" } instead of Variable { resulting_type: "MyFb" }. The subsequent .foo member lookup then fails because the REF function has no foo member.

Non-call contexts (e.g. assignments like ref := instance) are unaffected because they use the default resolving strategy [Variable, POU, DataType], where Variable runs first and correctly finds the local.

Notes

• Renaming the variable to anything other than ref (e.g. reference, myRef) works around the issue.
• The same problem would apply to any variable whose name collides with a builtin function name under case-insensitive matching.