compiler: make sure zero-sized array sizeof/alignof/offset of are correct

compiler/sizes.go

@@ -21,12 +21,6 @@ func (s *stdSizes) Alignof(T types.Type) int64 {
 	// of alignment of the elements and fields, respectively.
 	switch t := T.Underlying().(type) {
 	case *types.Array:
-		if t.Len() == 0 {
-			// 0-sized arrays, always have 0 size.
-			// And from the spec, should have an alignment of _at least_ 1
-			return 1
-		}
-
 		// spec: "For a variable x of array type: unsafe.Alignof(x)
 		// is the same as unsafe.Alignof(x[0]), but at least 1."
 		return s.Alignof(t.Elem())
@@ -51,7 +45,11 @@ func (s *stdSizes) Alignof(T types.Type) int64 {
 		if t.Info()&types.IsString != 0 {
 			return s.PtrSize
 		}
+	case *types.Signature:
+		// Even though functions in tinygo are 2 pointers, they are not 2 pointer aligned
+		return s.PtrSize
 	}
+
 	a := s.Sizeof(T) // may be 0
 	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
 	if a < 1 {

testdata/reflect.go

@@ -347,6 +347,13 @@ func main() {
 		println("errorValue.Implements(errorType) was true, expected false")
 	}
 
+	println("\nalignment / offset:")
+	v2 := struct {
+		noCompare [0]func()
+		data      byte
+	}{}
+	println("struct{[0]func(); byte}:", unsafe.Offsetof(v2.data) == uintptr(unsafe.Pointer(&v2.data))-uintptr(unsafe.Pointer(&v2)))
+
 	println("\nstruct tags")
 	TestStructTag()
 

testdata/reflect.txt

@@ -405,6 +405,9 @@ offset for int64 matches: true
 offset for complex128 matches: true
 type assertion succeeded for unreferenced type
 
+alignment / offset:
+struct{[0]func(); byte}: true
+
 struct tags
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