GALA-E0106 — Type named like a Go predeclared type, builtin function or std

When it fires. A type is declared with one of these names:

a Go predeclared type: bool, byte, rune, string, error, any, comparable, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr, float32, float64, complex64 or complex128;
a Go builtin function: append, cap, clear, close, complex, copy, delete, imag, len, make, max, min, new, panic, print, println, real or recover;
std, the name of GALA’s standard library package.

The rule covers every kind of type declaration: a shorthand or block struct, an interface, an alias, an opaque type, a sealed type and each of its cases, and a type parameter, at the top level or in a body.

Minimal repro.

package main

struct error(Code int, Msg string)

func lookup(code int) error = error(code, "not found")

func main() {
    Println(lookup(404).Msg)
}

Error output.

error[GALA-E0106]: type error is named like a Go predeclared type
  --> main.gala:3:8
  |
3 | struct error(Code int, Msg string)
  |        ^^^^^ rename the type
  |
  = hint: rename the type; GALA reads error as Go's own type wherever it is written

Fix. Rename the type:

package main

struct NotFound(Code int, Msg string)

func lookup(code int) NotFound = NotFound(code, "not found")

func main() {
    Println(lookup(404).Msg)
}

Rationale. GALA reads a predeclared type name as Go’s type in every type position, so a type declared with that name could not be written as a type. In the repro, the result type error is Go’s error interface, not the struct, and the program used to fail on an unrelated-looking message (error does not implement error). A value, a field or a function may still take such a name: there the name means the binding, and in a type position Go’s type.

A type named like a builtin function or std hides, in the Go GALA generates for its package, the builtin or the package that Go calls, so the program would fail in go build or depend on which helpers the transpiler happens to use. The message and hint say which kind of name it is:

package main

struct len(Items int)

func main() {
    Println(len(3).Items)
}

error[GALA-E0106]: type len is named like a Go builtin function
  --> main.gala:3:8
  |
3 | struct len(Items int)
  |        ^^^ rename the type
  |
  = hint: rename the type; it would hide Go's builtin len, which the generated Go calls

GALA-E0106 — Type named like a Go predeclared type, builtin function or std

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