go/types, types2: report struct type for literals with too few/many elements

This change essentially matches the 1.17 compiler error message for
this error.

Fixes #51877.

Change-Id: I24ec2f9cc93d8cd2283d097332a39bc1a0eed3a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/394914
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/expr.go

@@ -1429,7 +1429,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
 					}
 					check.expr(x, e)
 					if i >= len(fields) {
-						check.error(x, "too many values in struct literal")
+						check.errorf(x, "too many values in %s{…}", base)
 						break // cannot continue
 					}
 					// i < len(fields)
@@ -1442,7 +1442,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
 					check.assignment(x, etyp, "struct literal")
 				}
 				if len(e.ElemList) < len(fields) {
-					check.error(e.Rbrace, "too few values in struct literal")
+					check.errorf(e.Rbrace, "too few values in %s{…}", base)
 					// ok to continue
 				}
 			}

src/cmd/compile/internal/types2/testdata/fixedbugs/issue51877.go

@@ -0,0 +1,18 @@
+// Copyright 2013 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
+
+type S struct {
+	f1 int
+	f2 bool
+}
+
+var (
+	_ = S{0}                    /* ERROR too few values in S{…} */
+	_ = struct{ f1, f2 int }{0} /* ERROR too few values in struct{f1 int; f2 int}{…} */
+
+	_ = S{0, true, "foo" /* ERROR too many values in S{…} */}
+	_ = struct{ f1, f2 int }{0, 1, 2 /* ERROR too many values in struct{f1 int; f2 int}{…} */}
+)

src/go/types/expr.go

@@ -1404,7 +1404,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 					}
 					check.expr(x, e)
 					if i >= len(fields) {
-						check.error(x, _InvalidStructLit, "too many values in struct literal")
+						check.errorf(x, _InvalidStructLit, "too many values in %s{…}", base)
 						break // cannot continue
 					}
 					// i < len(fields)
@@ -1419,7 +1419,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 					check.assignment(x, etyp, "struct literal")
 				}
 				if len(e.Elts) < len(fields) {
-					check.error(inNode(e, e.Rbrace), _InvalidStructLit, "too few values in struct literal")
+					check.errorf(inNode(e, e.Rbrace), _InvalidStructLit, "too few values in %s{…}", base)
 					// ok to continue
 				}
 			}

src/go/types/testdata/fixedbugs/issue51877.go

@@ -0,0 +1,18 @@
+// Copyright 2013 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
+
+type S struct {
+	f1 int
+	f2 bool
+}
+
+var (
+	_ = S{0}                    /* ERROR too few values in S{…} */
+	_ = struct{ f1, f2 int }{0} /* ERROR too few values in struct{f1 int; f2 int}{…} */
+
+	_ = S{0, true, "foo" /* ERROR too many values in S{…} */}
+	_ = struct{ f1, f2 int }{0, 1, 2 /* ERROR too many values in struct{f1 int; f2 int}{…} */}
+)