go/types, types2: better error message for type parameter field access

Fixes #50516.

Also call DefPredeclaredTestFuncs in TestFixedbugs so it can be
run independently again.

Change-Id: I78d4cc11790b1543a2545a7ab297a223b3d5e3c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/376954
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

5 files changed, 39 insertions, 36 deletions

diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index bd62e825af..1c3bf48b08 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -542,39 +542,26 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 			goto Error
 		}
 
-		if isInterfacePtr(x.typ) {
-			check.errorf(e.Sel, "%s.%s undefined (type %s is pointer to interface, not interface)", x.expr, sel, x.typ)
-			goto Error
-		}
-
 		var why string
-		if tpar, _ := x.typ.(*TypeParam); tpar != nil {
-			// Type parameter bounds don't specify fields, so don't mention "field".
-			// TODO(gri) Type constraints may have accessible fields now. Revisit this.
-			if tname := tpar.iface().obj; tname != nil {
-				why = check.sprintf("interface %s has no method %s", tname.name, sel)
-			} else {
-				why = check.sprintf("type bound for %s has no method %s", x.typ, sel)
-			}
+		if isInterfacePtr(x.typ) {
+			why = check.sprintf("type %s is pointer to interface, not interface", x.typ)
 		} else {
 			why = check.sprintf("type %s has no field or method %s", x.typ, sel)
-		}
-
-		// Check if capitalization of sel matters and provide better error message in that case.
-		// TODO(gri) This code only looks at the first character but LookupFieldOrMethod has an
-		//           (internal) mechanism for case-insensitive lookup. Should use that instead.
-		if len(sel) > 0 {
-			var changeCase string
-			if r := rune(sel[0]); unicode.IsUpper(r) {
-				changeCase = string(unicode.ToLower(r)) + sel[1:]
-			} else {
-				changeCase = string(unicode.ToUpper(r)) + sel[1:]
-			}
-			if obj, _, _ = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, changeCase); obj != nil {
-				why += ", but does have " + changeCase
+			// Check if capitalization of sel matters and provide better error message in that case.
+			// TODO(gri) This code only looks at the first character but LookupFieldOrMethod has an
+			//           (internal) mechanism for case-insensitive lookup. Should use that instead.
+			if len(sel) > 0 {
+				var changeCase string
+				if r := rune(sel[0]); unicode.IsUpper(r) {
+					changeCase = string(unicode.ToLower(r)) + sel[1:]
+				} else {
+					changeCase = string(unicode.ToUpper(r)) + sel[1:]
+				}
+				if obj, _, _ = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, changeCase); obj != nil {
+					why += ", but does have " + changeCase
+				}
 			}
 		}
-
 		check.errorf(e.Sel, "%s.%s undefined (%s)", x.expr, sel, why)
 		goto Error
 	}
diff --git a/src/cmd/compile/internal/types2/check_test.go b/src/cmd/compile/internal/types2/check_test.go
index 1868ad0c6e..7efa512164 100644
--- a/src/cmd/compile/internal/types2/check_test.go
+++ b/src/cmd/compile/internal/types2/check_test.go
@@ -295,10 +295,13 @@ func TestManual(t *testing.T) {
 
 // TODO(gri) go/types has extra TestLongConstants and TestIndexRepresentability tests
 
-func TestCheck(t *testing.T)     { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/check", 55, false) } // TODO(gri) narrow column tolerance
-func TestSpec(t *testing.T)      { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/spec", 0, false) }
-func TestExamples(t *testing.T)  { testDirFiles(t, "testdata/examples", 0, false) }
-func TestFixedbugs(t *testing.T) { testDirFiles(t, "testdata/fixedbugs", 0, false) }
+func TestCheck(t *testing.T)    { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/check", 55, false) } // TODO(gri) narrow column tolerance
+func TestSpec(t *testing.T)     { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/spec", 0, false) }
+func TestExamples(t *testing.T) { testDirFiles(t, "testdata/examples", 0, false) }
+func TestFixedbugs(t *testing.T) {
+	DefPredeclaredTestFuncs()
+	testDirFiles(t, "testdata/fixedbugs", 0, false)
+}
 
 func testDirFiles(t *testing.T, dir string, colDelta uint, manual bool) {
 	testenv.MustHaveGoBuild(t)
diff --git a/src/cmd/compile/internal/types2/testdata/check/typeparams.go2 b/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
index 007157ea0f..ef58241519 100644
--- a/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
@@ -519,13 +519,13 @@ func _[P C[P]] (x P) {
 type I interface {}
 
 func _[P I] (x P) {
-	x.m /* ERROR interface I has no method m */ ()
+	x.m /* ERROR type P has no field or method m */ ()
 }
 
 func _[P interface{}] (x P) {
-	x.m /* ERROR type bound for P has no method m */ ()
+	x.m /* ERROR type P has no field or method m */ ()
 }
 
 func _[P any] (x P) {
-	x.m /* ERROR type bound for P has no method m */ ()
+	x.m /* ERROR type P has no field or method m */ ()
 }
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50417.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50417.go2
index c05987e5ea..b6454ab003 100644
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50417.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50417.go2
@@ -58,7 +58,7 @@ type PSfm *Sfm
 func f3[P interface{ PSfm }](p P) {
         _ = p.f
         p.f = 0
-        p.m /* ERROR type bound for P has no method m */ ()
+        p.m /* ERROR type P has no field or method m */ ()
 }
 
 var _ = f3[PSfm]
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50516.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50516.go2
new file mode 100644
index 0000000000..f73015e2be
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50516.go2
@@ -0,0 +1,13 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func _[P struct{ f int }](x P) {
+	_ = x.g // ERROR type P has no field or method g
+}
+
+func _[P struct{ f int } | struct{ g int }](x P) {
+	_ = x.g // ERROR type P has no field or method g
+}