fix hashing of generic field names

Trying to make Go master work, I noticed that crypto/tls still failed to
build. The reason was generic structs; we would badly obfuscate their
field names when the types are instantiated:

	> garble build
	[stderr]
	# test/main
	Z4ZpcbMj.go:4: unknown field 'FOpszkrN' in struct literal of type SYdpWfK5[string]
	Z4ZpcbMj.go:5: m8hLTotb.FypXrbTd undefined (type SYdpWfK5[string] has no field or method FypXrbTd)
	exit status 2

See the added comment for what happened and how we fixed it. And add tests.

main.go

@@ -1359,14 +1359,14 @@ func (tf *transformer) typecheck(files []*ast.File) error {
 	// A bit hacky, but I could not find an easier way to do this.
 	for _, obj := range tf.info.Defs {
 		if obj != nil {
-			tf.recordType(obj.Type())
+			tf.recordType(obj.Type(), nil)
 		}
 	}
 	for name, obj := range tf.info.Uses {
 		if obj == nil {
 			continue
 		}
-		tf.recordType(obj.Type())
+		tf.recordType(obj.Type(), nil)
 
 		// Record into KnownEmbeddedAliasFields.
 		obj, ok := obj.(*types.TypeName)
@@ -1388,7 +1388,7 @@ func (tf *transformer) typecheck(files []*ast.File) error {
 		cachedOutput.KnownEmbeddedAliasFields[vrStr] = aliasTypeName
 	}
 	for _, tv := range tf.info.Types {
-		tf.recordType(tv.Type)
+		tf.recordType(tv.Type, nil)
 	}
 	return nil
 }
@@ -1396,27 +1396,38 @@ func (tf *transformer) typecheck(files []*ast.File) error {
 // recordType visits every reachable type after typechecking a package.
 // Right now, all it does is fill the fieldToStruct field.
 // Since types can be recursive, we need a map to avoid cycles.
-func (tf *transformer) recordType(t types.Type) {
-	if tf.recordTypeDone[t] {
+func (tf *transformer) recordType(used, origin types.Type) {
+	if tf.recordTypeDone[used] {
 		return
 	}
-	tf.recordTypeDone[t] = true
-	switch t := t.(type) {
-	case interface{ Elem() types.Type }:
-		tf.recordType(t.Elem())
-	case *types.Named:
-		tf.recordType(t.Underlying())
-	}
-	strct, _ := t.(*types.Struct)
-	if strct == nil {
-		return
+	if origin == nil {
+		origin = used
 	}
-	for i := 0; i < strct.NumFields(); i++ {
-		field := strct.Field(i)
-		tf.fieldToStruct[field] = strct
+	type Container interface{ Elem() types.Type }
+	tf.recordTypeDone[used] = true
+	switch used := used.(type) {
+	case Container:
+		origin := origin.(Container)
+		tf.recordType(used.Elem(), origin.Elem())
+	case *types.Named:
+		// If we have a generic struct like
+		//
+		//	type Foo[T any] struct { Bar T }
+		//
+		// then we want the hashing to use the original "Bar T",
+		// because otherwise different instances like "Bar int" and "Bar bool"
+		// will result in different hashes and the field names will break.
+		// Ensure we record the original generic struct, if there is one.
+		tf.recordType(used.Underlying(), used.Origin().Underlying())
+	case *types.Struct:
+		origin := origin.(*types.Struct)
+		for i := 0; i < used.NumFields(); i++ {
+			field := used.Field(i)
+			tf.fieldToStruct[field] = origin
 
-		if field.Embedded() {
-			tf.recordType(field.Type())
+			if field.Embedded() {
+				tf.recordType(field.Type(), origin.Field(i).Type())
+			}
 		}
 	}
 }

testdata/scripts/typeparams.txt

@@ -12,14 +12,22 @@ go 1.18
 package main
 
 func main() {
-	//var _ GenericVector[int]
 	GenericFunc[int, int](1, 2)
+	var _ GenericVector[int]
+
+	g := GenericGraph[string]{Content: "Foo"}
+	g.Edges = make([]GenericGraph[string], 1)
 }
 
 func GenericFunc[GenericParamA, B any](x GenericParamA, y B) {}
 
 type GenericVector[GenericParamT any] []GenericParamT
 
+type GenericGraph[T any] struct {
+	Content T
+	Edges []GenericGraph[T]
+}
+
 type PredeclaredSignedInteger interface {
 	int | int8 | int16 | int32 | int64
 }