[dev.typeparams] cmd/compile/internal/types2: move embedding positions from Checker to Interface

This change moves the position information to the place where it
is actually used. It also simplifies getting rid of it after use.

In the process, fixed a latent bug: Before this CL, embedded types
were sorted, but the corresponding embedding positions were not.
Removed the sorting altogether as it is not needed for type-checking.

Change-Id: I48003f317196d814326424430336b6cb222fdee6
Reviewed-on: https://go-review.googlesource.com/c/go/+/331514
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

5 files changed, 28 insertions, 43 deletions

diff --git a/src/cmd/compile/internal/types2/check.go b/src/cmd/compile/internal/types2/check.go
index 5d3c2c8ad2..071afef058 100644
--- a/src/cmd/compile/internal/types2/check.go
+++ b/src/cmd/compile/internal/types2/check.go
@@ -82,12 +82,11 @@ type Checker struct {
 	conf *Config
 	pkg  *Package
 	*Info
-	version version                     // accepted language version
-	nextID  uint64                      // unique Id for type parameters (first valid Id is 1)
-	objMap  map[Object]*declInfo        // maps package-level objects and (non-interface) methods to declaration info
-	impMap  map[importKey]*Package      // maps (import path, source directory) to (complete or fake) package
-	posMap  map[*Interface][]syntax.Pos // maps interface types to lists of embedded interface positions
-	typMap  map[string]*Named           // maps an instantiated named type hash to a *Named type
+	version version                // accepted language version
+	nextID  uint64                 // unique Id for type parameters (first valid Id is 1)
+	objMap  map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
+	impMap  map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
+	typMap  map[string]*Named      // maps an instantiated named type hash to a *Named type
 
 	// pkgPathMap maps package names to the set of distinct import paths we've
 	// seen for that name, anywhere in the import graph. It is used for
@@ -189,7 +188,6 @@ func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
 		version: version,
 		objMap:  make(map[Object]*declInfo),
 		impMap:  make(map[importKey]*Package),
-		posMap:  make(map[*Interface][]syntax.Pos),
 		typMap:  make(map[string]*Named),
 	}
 }
diff --git a/src/cmd/compile/internal/types2/interface.go b/src/cmd/compile/internal/types2/interface.go
index 499b078dc0..e667830db3 100644
--- a/src/cmd/compile/internal/types2/interface.go
+++ b/src/cmd/compile/internal/types2/interface.go
@@ -14,11 +14,18 @@ func (check *Checker) interfaceType(ityp *Interface, iface *syntax.InterfaceType
 	var tlist []syntax.Expr // types collected from all type lists
 	var tname *syntax.Name  // most recent "type" name
 
+	addEmbedded := func(pos syntax.Pos, typ Type) {
+		ityp.embeddeds = append(ityp.embeddeds, typ)
+		if ityp.embedPos == nil {
+			ityp.embedPos = new([]syntax.Pos)
+		}
+		*ityp.embedPos = append(*ityp.embedPos, pos)
+	}
+
 	for _, f := range iface.MethodList {
 		if f.Name == nil {
 			// We have an embedded type; possibly a union of types.
-			ityp.embeddeds = append(ityp.embeddeds, parseUnion(check, flattenUnion(nil, f.Type)))
-			check.posMap[ityp] = append(check.posMap[ityp], f.Type.Pos())
+			addEmbedded(f.Type.Pos(), parseUnion(check, flattenUnion(nil, f.Type)))
 			continue
 		}
 		// f.Name != nil
@@ -89,10 +96,9 @@ func (check *Checker) interfaceType(ityp *Interface, iface *syntax.InterfaceType
 
 	// If we saw a type list, add it like an embedded union.
 	if tlist != nil {
-		ityp.embeddeds = append(ityp.embeddeds, parseUnion(check, tlist))
 		// Types T in a type list are added as ~T expressions but we don't
 		// have the position of the '~'. Use the first type position instead.
-		check.posMap[ityp] = append(check.posMap[ityp], tlist[0].(*syntax.Operation).X.Pos())
+		addEmbedded(tlist[0].(*syntax.Operation).X.Pos(), parseUnion(check, tlist))
 	}
 
 	// All methods and embedded elements for this interface are collected;
@@ -106,8 +112,8 @@ func (check *Checker) interfaceType(ityp *Interface, iface *syntax.InterfaceType
 	}
 
 	// sort for API stability
+	// (don't sort embeddeds: they must correspond to *embedPos entries)
 	sortMethods(ityp.methods)
-	sortTypes(ityp.embeddeds)
 
 	// Compute type set with a non-nil *Checker as soon as possible
 	// to report any errors. Subsequent uses of type sets should be
@@ -227,14 +233,13 @@ func newTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *TypeSet {
 
 	// collect embedded elements
 	var allTypes Type
-	var posList []syntax.Pos
-	if check != nil {
-		posList = check.posMap[ityp]
-	}
 	for i, typ := range ityp.embeddeds {
+		// The embedding position is nil for imported interfaces
+		// and also for interface copies after substitution (but
+		// in that case we don't need to report errors again).
 		var pos syntax.Pos // embedding position
-		if posList != nil {
-			pos = posList[i]
+		if ityp.embedPos != nil {
+			pos = (*ityp.embedPos)[i]
 		}
 		var types Type
 		switch t := under(typ).(type) {
@@ -268,6 +273,7 @@ func newTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *TypeSet {
 		}
 		allTypes = intersect(allTypes, types)
 	}
+	ityp.embedPos = nil // not needed anymore (errors have been reported)
 
 	// process todo's (this only happens if check == nil)
 	for i := 0; i < len(todo); i += 2 {
@@ -287,24 +293,6 @@ func newTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *TypeSet {
 	return ityp.tset
 }
 
-func sortTypes(list []Type) {
-	sort.Stable(byUniqueTypeName(list))
-}
-
-// byUniqueTypeName named type lists can be sorted by their unique type names.
-type byUniqueTypeName []Type
-
-func (a byUniqueTypeName) Len() int           { return len(a) }
-func (a byUniqueTypeName) Less(i, j int) bool { return sortObj(a[i]).less(sortObj(a[j])) }
-func (a byUniqueTypeName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
-
-func sortObj(t Type) *object {
-	if named := asNamed(t); named != nil {
-		return &named.obj.object
-	}
-	return nil
-}
-
 func sortMethods(list []*Func) {
 	sort.Sort(byUniqueMethodName(list))
 }
diff --git a/src/cmd/compile/internal/types2/sizeof_test.go b/src/cmd/compile/internal/types2/sizeof_test.go
index 0b1f7dacad..82e1221b67 100644
--- a/src/cmd/compile/internal/types2/sizeof_test.go
+++ b/src/cmd/compile/internal/types2/sizeof_test.go
@@ -28,7 +28,7 @@ func TestSizeof(t *testing.T) {
 		{Tuple{}, 12, 24},
 		{Signature{}, 44, 88},
 		{Union{}, 24, 48},
-		{Interface{}, 40, 80},
+		{Interface{}, 44, 88},
 		{Map{}, 16, 32},
 		{Chan{}, 12, 24},
 		{Named{}, 84, 160},
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 38bd07b8a2..db01c36f7a 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -316,7 +316,6 @@ func (subst *subster) typ(typ Type) Type {
 			if subst.check == nil {
 				panic("internal error: cannot instantiate interfaces yet")
 			}
-			subst.check.posMap[iface] = subst.check.posMap[t] // satisfy completeInterface requirement
 			return iface
 		}
 
diff --git a/src/cmd/compile/internal/types2/type.go b/src/cmd/compile/internal/types2/type.go
index 122e408ead..2cfcabbdb5 100644
--- a/src/cmd/compile/internal/types2/type.go
+++ b/src/cmd/compile/internal/types2/type.go
@@ -264,10 +264,11 @@ func (s *Signature) Variadic() bool { return s.variadic }
 
 // An Interface represents an interface type.
 type Interface struct {
-	obj       Object  // type name object defining this interface; or nil (for better error messages)
-	methods   []*Func // ordered list of explicitly declared methods
-	embeddeds []Type  // ordered list of explicitly embedded elements
-	complete  bool    // indicates that obj, methods, and embeddeds are set and type set can be computed
+	obj       Object        // type name object defining this interface; or nil (for better error messages)
+	methods   []*Func       // ordered list of explicitly declared methods
+	embeddeds []Type        // ordered list of explicitly embedded elements
+	embedPos  *[]syntax.Pos // positions of embedded elements; or nil (for error messages) - use pointer to save space
+	complete  bool          // indicates that all fields (except for tset) are set up
 
 	tset *TypeSet // type set described by this interface, computed lazily
 }
@@ -322,7 +323,6 @@ func NewInterfaceType(methods []*Func, embeddeds []Type) *Interface {
 
 	// sort for API stability
 	sortMethods(methods)
-	sortTypes(embeddeds)
 
 	typ.methods = methods
 	typ.embeddeds = embeddeds