[dev.regabi] go/types: factor out sorting of methods

This is a port of CL 285993 to go/types.

Change-Id: I7560cf1176fea5de2c54786a086e547c73294a60
Reviewed-on: https://go-review.googlesource.com/c/go/+/289717
Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

3 files changed, 24 insertions, 11 deletions

diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 148edbfb76..954a7ca987 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -6,8 +6,6 @@
 
 package types
 
-import "sort"
-
 func isNamed(typ Type) bool {
 	if _, ok := typ.(*Basic); ok {
 		return ok
@@ -273,8 +271,8 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 					p = p.prev
 				}
 				if debug {
-					assert(sort.IsSorted(byUniqueMethodName(a)))
-					assert(sort.IsSorted(byUniqueMethodName(b)))
+					assertSortedMethods(a)
+					assertSortedMethods(b)
 				}
 				for i, f := range a {
 					g := b[i]
diff --git a/src/go/types/type.go b/src/go/types/type.go
index 087cda429d..66e194e967 100644
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -4,8 +4,6 @@
 
 package types
 
-import "sort"
-
 // A Type represents a type of Go.
 // All types implement the Type interface.
 type Type interface {
@@ -301,8 +299,8 @@ func NewInterfaceType(methods []*Func, embeddeds []Type) *Interface {
 	}
 
 	// sort for API stability
-	sort.Sort(byUniqueMethodName(methods))
-	sort.Stable(byUniqueTypeName(embeddeds))
+	sortMethods(methods)
+	sortTypes(embeddeds)
 
 	typ.methods = methods
 	typ.embeddeds = embeddeds
@@ -396,7 +394,7 @@ func (t *Interface) Complete() *Interface {
 	}
 
 	if methods != nil {
-		sort.Sort(byUniqueMethodName(methods))
+		sortMethods(methods)
 		t.allMethods = methods
 	}
 
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 2b398010f4..311a970051 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -518,8 +518,8 @@ func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, d
 	}
 
 	// sort for API stability
-	sort.Sort(byUniqueMethodName(ityp.methods))
-	sort.Stable(byUniqueTypeName(ityp.embeddeds))
+	sortMethods(ityp.methods)
+	sortTypes(ityp.embeddeds)
 
 	check.later(func() { check.completeInterface(ityp) })
 }
@@ -613,6 +613,10 @@ func (check *Checker) completeInterface(ityp *Interface) {
 	}
 }
 
+func sortTypes(list []Type) {
+	sort.Stable(byUniqueTypeName(list))
+}
+
 // byUniqueTypeName named type lists can be sorted by their unique type names.
 type byUniqueTypeName []Type
 
@@ -627,6 +631,19 @@ func sortName(t Type) string {
 	return ""
 }
 
+func sortMethods(list []*Func) {
+	sort.Sort(byUniqueMethodName(list))
+}
+
+func assertSortedMethods(list []*Func) {
+	if !debug {
+		panic("internal error: assertSortedMethods called outside debug mode")
+	}
+	if !sort.IsSorted(byUniqueMethodName(list)) {
+		panic("internal error: methods not sorted")
+	}
+}
+
 // byUniqueMethodName method lists can be sorted by their unique method names.
 type byUniqueMethodName []*Func