[dev.typeparams] cmd/compile/internal/types2: use same sort criteria for methods as compiler

Note: This invalidates the implementation of MethodSet further (it
also has not been updated to accomodate for type parameters). But
types2 doesn't make use of it. We should remove it.

Change-Id: Ia2601bdd59b3f3ee0b72bc2512153c42bf5053b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/285994
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/types2/object.go

@@ -330,6 +330,36 @@ func (obj *Func) FullName() string {
 // Scope returns the scope of the function's body block.
 func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
 
+// Less reports whether function a is ordered before function b.
+//
+// Functions are ordered exported before non-exported, then by name,
+// and finally (for non-exported functions) by package path.
+//
+// TODO(gri) The compiler also sorts by package height before package
+//           path for non-exported names.
+func (a *Func) less(b *Func) bool {
+	if a == b {
+		return false
+	}
+
+	// Exported functions before non-exported.
+	ea := isExported(a.name)
+	eb := isExported(b.name)
+	if ea != eb {
+		return ea
+	}
+
+	// Order by name and then (for non-exported names) by package.
+	if a.name != b.name {
+		return a.name < b.name
+	}
+	if !ea {
+		return a.pkg.path < b.pkg.path
+	}
+
+	return false
+}
+
 func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
 
 // A Label represents a declared label.

src/cmd/compile/internal/types2/typexpr.go

@@ -1064,7 +1064,7 @@ func assertSortedMethods(list []*Func) {
 type byUniqueMethodName []*Func
 
 func (a byUniqueMethodName) Len() int           { return len(a) }
-func (a byUniqueMethodName) Less(i, j int) bool { return a[i].Id() < a[j].Id() }
+func (a byUniqueMethodName) Less(i, j int) bool { return a[i].less(a[j]) }
 func (a byUniqueMethodName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 
 func (check *Checker) tag(t *syntax.BasicLit) string {