go/types, types2: enable new type inference

Enable new type inference and compare result with old inference
implementation - the result must be identical in a correct program.

Change-Id: Ic802d29fcee744f6f826d5e433a3d0c0e73b68e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/464341
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>

7 files changed, 69 insertions, 36 deletions

diff --git a/src/cmd/compile/internal/types2/infer.go b/src/cmd/compile/internal/types2/infer.go
index be88f5db91..671ce6a640 100644
--- a/src/cmd/compile/internal/types2/infer.go
+++ b/src/cmd/compile/internal/types2/infer.go
@@ -13,13 +13,7 @@ import (
 	"strings"
 )
 
-// infer attempts to infer the complete set of type arguments for generic function instantiation/call
-// based on the given type parameters tparams, type arguments targs, function parameters params, and
-// function arguments args, if any. There must be at least one type parameter, no more type arguments
-// than type parameters, and params and args must match in number (incl. zero).
-// If successful, infer returns the complete list of type arguments, one for each type parameter.
-// Otherwise the result is nil and appropriate errors will be reported.
-//
+// infer1 is an implementation of infer.
 // Inference proceeds as follows. Starting with given type arguments:
 //
 //  1. apply FTI (function type inference) with typed arguments,
@@ -28,11 +22,7 @@ import (
 //  4. apply CTI.
 //
 // The process stops as soon as all type arguments are known or an error occurs.
-func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (result []Type) {
-	if useNewTypeInference {
-		return check.infer2(pos, tparams, targs, params, args)
-	}
-
+func (check *Checker) infer1(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand, silent bool) (result []Type) {
 	if debug {
 		defer func() {
 			assert(result == nil || len(result) == len(tparams))
@@ -142,6 +132,9 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type,
 	u := newUnifier(tparams, targs)
 
 	errorf := func(kind string, tpar, targ Type, arg *operand) {
+		if silent {
+			return
+		}
 		// provide a better error message if we can
 		targs, index := u.inferred()
 		if index == 0 {
@@ -260,7 +253,9 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type,
 	// At least one type argument couldn't be inferred.
 	assert(targs != nil && index >= 0 && targs[index] == nil)
 	tpar := tparams[index]
-	check.errorf(pos, CannotInferTypeArgs, "cannot infer %s (%s)", tpar.obj.name, tpar.obj.pos)
+	if !silent {
+		check.errorf(pos, CannotInferTypeArgs, "cannot infer %s (%s)", tpar.obj.name, tpar.obj.pos)
+	}
 	return nil
 }
 
diff --git a/src/cmd/compile/internal/types2/infer2.go b/src/cmd/compile/internal/types2/infer2.go
index 27e951ce01..6f0c1ddff5 100644
--- a/src/cmd/compile/internal/types2/infer2.go
+++ b/src/cmd/compile/internal/types2/infer2.go
@@ -11,14 +11,30 @@ import (
 	. "internal/types/errors"
 )
 
-const useNewTypeInference = false
-
-// infer2 attempts to infer the complete set of type arguments for generic function instantiation/call
+// infer attempts to infer the complete set of type arguments for generic function instantiation/call
 // based on the given type parameters tparams, type arguments targs, function parameters params, and
 // function arguments args, if any. There must be at least one type parameter, no more type arguments
 // than type parameters, and params and args must match in number (incl. zero).
 // If successful, infer returns the complete list of given and inferred type arguments, one for each
 // type parameter. Otherwise the result is nil and appropriate errors will be reported.
+func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) []Type {
+	r2 := check.infer2(pos, tparams, targs, params, args)
+	r1 := check.infer1(pos, tparams, targs, params, args, r2 == nil) // be silent on errors if infer2 failed
+	assert(len(r2) == len(r1))
+	for i, targ2 := range r2 {
+		targ1 := r1[i]
+		var c comparer
+		c.ignoreInvalids = true
+		if !c.identical(targ2, targ1, nil) {
+			tpar := tparams[i]
+			check.dump("%v: type argument for %s: infer1: %s, infer2: %s", tpar.Obj().Pos(), tpar, targ1, targ2)
+			panic("inconsistent type inference")
+		}
+	}
+	return r2
+}
+
+// infer2 is an implementation of infer.
 func (check *Checker) infer2(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (inferred []Type) {
 	if debug {
 		defer func() {
diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index c30badfe17..2e6067652b 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -201,7 +201,8 @@ func (p *ifacePair) identical(q *ifacePair) bool {
 
 // A comparer is used to compare types.
 type comparer struct {
-	ignoreTags bool // if set, identical ignores struct tags
+	ignoreTags     bool // if set, identical ignores struct tags
+	ignoreInvalids bool // if set, identical treats an invalid type as identical to any type
 }
 
 // For changes to this code the corresponding changes should be made to unifier.nify.
@@ -210,6 +211,10 @@ func (c *comparer) identical(x, y Type, p *ifacePair) bool {
 		return true
 	}
 
+	if c.ignoreInvalids && (x == Typ[Invalid] || y == Typ[Invalid]) {
+		return true
+	}
+
 	switch x := x.(type) {
 	case *Basic:
 		// Basic types are singletons except for the rune and byte
diff --git a/src/go/types/generate_test.go b/src/go/types/generate_test.go
index 707d17e920..c78e94eadc 100644
--- a/src/go/types/generate_test.go
+++ b/src/go/types/generate_test.go
@@ -207,7 +207,7 @@ func fixInferSig(f *ast.File) {
 	ast.Inspect(f, func(n ast.Node) bool {
 		switch n := n.(type) {
 		case *ast.FuncDecl:
-			if n.Name.Name == "infer" || n.Name.Name == "infer2" {
+			if n.Name.Name == "infer" || n.Name.Name == "infer1" || n.Name.Name == "infer2" {
 				// rewrite (pos token.Pos, ...) to (posn positioner, ...)
 				par := n.Type.Params.List[0]
 				if len(par.Names) == 1 && par.Names[0].Name == "pos" {
@@ -228,8 +228,9 @@ func fixInferSig(f *ast.File) {
 						n.Args[0] = arg
 						return false
 					}
-				case "errorf", "infer2":
+				case "errorf", "infer1", "infer2":
 					// rewrite check.errorf(pos, ...) to check.errorf(posn, ...)
+					// rewrite check.infer1(pos, ...) to check.infer1(posn, ...)
 					// rewrite check.infer2(pos, ...) to check.infer2(posn, ...)
 					if ident, _ := n.Args[0].(*ast.Ident); ident != nil && ident.Name == "pos" {
 						pos := n.Args[0].Pos()
diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index 3ee4f50413..93a43d39ea 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -15,13 +15,7 @@ import (
 	"strings"
 )
 
-// infer attempts to infer the complete set of type arguments for generic function instantiation/call
-// based on the given type parameters tparams, type arguments targs, function parameters params, and
-// function arguments args, if any. There must be at least one type parameter, no more type arguments
-// than type parameters, and params and args must match in number (incl. zero).
-// If successful, infer returns the complete list of type arguments, one for each type parameter.
-// Otherwise the result is nil and appropriate errors will be reported.
-//
+// infer1 is an implementation of infer.
 // Inference proceeds as follows. Starting with given type arguments:
 //
 //  1. apply FTI (function type inference) with typed arguments,
@@ -30,11 +24,7 @@ import (
 //  4. apply CTI.
 //
 // The process stops as soon as all type arguments are known or an error occurs.
-func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (result []Type) {
-	if useNewTypeInference {
-		return check.infer2(posn, tparams, targs, params, args)
-	}
-
+func (check *Checker) infer1(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand, silent bool) (result []Type) {
 	if debug {
 		defer func() {
 			assert(result == nil || len(result) == len(tparams))
@@ -144,6 +134,9 @@ func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type,
 	u := newUnifier(tparams, targs)
 
 	errorf := func(kind string, tpar, targ Type, arg *operand) {
+		if silent {
+			return
+		}
 		// provide a better error message if we can
 		targs, index := u.inferred()
 		if index == 0 {
@@ -262,7 +255,9 @@ func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type,
 	// At least one type argument couldn't be inferred.
 	assert(targs != nil && index >= 0 && targs[index] == nil)
 	tpar := tparams[index]
-	check.errorf(posn, CannotInferTypeArgs, "cannot infer %s (%s)", tpar.obj.name, tpar.obj.pos)
+	if !silent {
+		check.errorf(posn, CannotInferTypeArgs, "cannot infer %s (%s)", tpar.obj.name, tpar.obj.pos)
+	}
 	return nil
 }
 
diff --git a/src/go/types/infer2.go b/src/go/types/infer2.go
index 711bd6b584..a0c2ac1c69 100644
--- a/src/go/types/infer2.go
+++ b/src/go/types/infer2.go
@@ -13,14 +13,30 @@ import (
 	. "internal/types/errors"
 )
 
-const useNewTypeInference = false
-
-// infer2 attempts to infer the complete set of type arguments for generic function instantiation/call
+// infer attempts to infer the complete set of type arguments for generic function instantiation/call
 // based on the given type parameters tparams, type arguments targs, function parameters params, and
 // function arguments args, if any. There must be at least one type parameter, no more type arguments
 // than type parameters, and params and args must match in number (incl. zero).
 // If successful, infer returns the complete list of given and inferred type arguments, one for each
 // type parameter. Otherwise the result is nil and appropriate errors will be reported.
+func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) []Type {
+	r2 := check.infer2(posn, tparams, targs, params, args)
+	r1 := check.infer1(posn, tparams, targs, params, args, r2 == nil) // be silent on errors if infer2 failed
+	assert(len(r2) == len(r1))
+	for i, targ2 := range r2 {
+		targ1 := r1[i]
+		var c comparer
+		c.ignoreInvalids = true
+		if !c.identical(targ2, targ1, nil) {
+			tpar := tparams[i]
+			check.dump("%v: type argument for %s: infer1: %s, infer2: %s", tpar.Obj().Pos(), tpar, targ1, targ2)
+			panic("inconsistent type inference")
+		}
+	}
+	return r2
+}
+
+// infer2 is an implementation of infer.
 func (check *Checker) infer2(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (inferred []Type) {
 	if debug {
 		defer func() {
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 9a156a040c..903b1445e9 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -203,7 +203,8 @@ func (p *ifacePair) identical(q *ifacePair) bool {
 
 // A comparer is used to compare types.
 type comparer struct {
-	ignoreTags bool // if set, identical ignores struct tags
+	ignoreTags     bool // if set, identical ignores struct tags
+	ignoreInvalids bool // if set, identical treats an invalid type as identical to any type
 }
 
 // For changes to this code the corresponding changes should be made to unifier.nify.
@@ -212,6 +213,10 @@ func (c *comparer) identical(x, y Type, p *ifacePair) bool {
 		return true
 	}
 
+	if c.ignoreInvalids && (x == Typ[Invalid] || y == Typ[Invalid]) {
+		return true
+	}
+
 	switch x := x.(type) {
 	case *Basic:
 		// Basic types are singletons except for the rune and byte