go/types, types2: quote user-supplied names in error messages

Use `' quotes (as in `foo') to differentiate from Go quotes.
Quoting prevents confusion when user-supplied names alter
the meaning of the error message.

For instance, report

        duplicate method `wanted'

rather than

        duplicate method wanted

Exceptions:
- don't quote _:
        `_' is ugly and not necessary
- don't quote after a ":":
        undefined name: foo
- don't quote if the name is used correctly in a statement:
        goto L jumps over variable declaration

Quoting is done with a helper function and can be centrally adjusted
and fine-tuned as needed.

Adjusted some test cases to explicitly include the quoted names.

Fixes #65790.

Change-Id: Icce667215f303ab8685d3e5cb00d540a2fd372ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/571396
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Griesemer <gri@google.com>

29 files changed, 168 insertions, 97 deletions

diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index a87474ad6c..b897a55212 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -25,7 +25,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 	if hasDots(call) && id != _Append {
 		check.errorf(dddErrPos(call),
 			InvalidDotDotDot,
-			invalidOp+"invalid use of ... with built-in %s", bin.name)
+			invalidOp+"invalid use of ... with built-in %s", quote(bin.name))
 		check.use(argList...)
 		return
 	}
@@ -210,7 +210,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 				if id == _Len {
 					code = InvalidLen
 				}
-				check.errorf(x, code, invalidArg+"%s for %s", x, bin.name)
+				check.errorf(x, code, invalidArg+"%s for %s", x, quote(bin.name))
 			}
 			return
 		}
@@ -533,7 +533,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 	case _Max, _Min:
 		// max(x, ...)
 		// min(x, ...)
-		check.verifyVersionf(call.Fun, go1_21, bin.name)
+		check.verifyVersionf(call.Fun, go1_21, quote(bin.name))
 
 		op := token.LSS
 		if id == _Max {
@@ -576,7 +576,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		if x.mode != constant_ {
 			x.mode = value
 			// A value must not be untyped.
-			check.assignment(x, &emptyInterface, "argument to "+bin.name)
+			check.assignment(x, &emptyInterface, "argument to "+quote(bin.name))
 			if x.mode == invalid {
 				return
 			}
@@ -641,7 +641,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		if nargs > 0 {
 			params = make([]Type, nargs)
 			for i, a := range args {
-				check.assignment(a, nil, "argument to "+predeclaredFuncs[id].name)
+				check.assignment(a, nil, "argument to "+quote(predeclaredFuncs[id].name))
 				if a.mode == invalid {
 					return
 				}
@@ -992,7 +992,7 @@ func (check *Checker) applyTypeFunc(f func(Type) Type, x *operand, id builtinId)
 		default:
 			panic("unreachable")
 		}
-		check.softErrorf(x, code, "%s not supported as argument to %s for go1.18 (see go.dev/issue/50937)", x, predeclaredFuncs[id].name)
+		check.softErrorf(x, code, "%s not supported as argument to %s for go1.18 (see go.dev/issue/50937)", x, quote(predeclaredFuncs[id].name))
 
 		// Construct a suitable new type parameter for the result type.
 		// The type parameter is placed in the current package so export/import
diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 0a5de6667e..ca9772ff41 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -719,7 +719,7 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr, def *TypeName
 					goto Error
 				}
 				if !exp.Exported() {
-					check.errorf(e.Sel, UnexportedName, "%s not exported by package %s", sel, pkg.name)
+					check.errorf(e.Sel, UnexportedName, "%s not exported by package %s", quote(sel), quote(pkg.name))
 					// ok to continue
 				}
 			}
diff --git a/src/cmd/compile/internal/types2/check.go b/src/cmd/compile/internal/types2/check.go
index bf613fd28b..2c6d77d6fd 100644
--- a/src/cmd/compile/internal/types2/check.go
+++ b/src/cmd/compile/internal/types2/check.go
@@ -298,7 +298,7 @@ func (check *Checker) initFiles(files []*syntax.File) {
 			check.files = append(check.files, file)
 
 		default:
-			check.errorf(file, MismatchedPkgName, "package %s; expected %s", name, pkg.name)
+			check.errorf(file, MismatchedPkgName, "package %s; expected %s", quote(name), quote(pkg.name))
 			// ignore this file
 		}
 	}
diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index c07a6b4dee..ed7784a6b8 100644
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -733,7 +733,7 @@ func (check *Checker) checkFieldUniqueness(base *Named) {
 					// For historical consistency, we report the primary error on the
 					// method, and the alt decl on the field.
 					err := check.newError(DuplicateFieldAndMethod)
-					err.addf(alt, "field and method with the same name %s", fld.name)
+					err.addf(alt, "field and method with the same name %s", quote(fld.name))
 					err.addAltDecl(fld)
 					err.report()
 				}
diff --git a/src/cmd/compile/internal/types2/format.go b/src/cmd/compile/internal/types2/format.go
index 442d219d1a..1b9cf606b7 100644
--- a/src/cmd/compile/internal/types2/format.go
+++ b/src/cmd/compile/internal/types2/format.go
@@ -14,6 +14,39 @@ import (
 	"strings"
 )
 
+// quote encloses s in `' quotes, as in `foo', except for _,
+// which is left alone.
+//
+// Use to prevent confusion when user supplied names alter the
+// meaning of an error message.
+//
+// For instance, report
+//
+//	duplicate method `wanted'
+//
+// rather than
+//
+//	duplicate method wanted
+//
+// Exceptions:
+//
+//   - don't quote _:
+//     `_' is ugly and not necessary
+//   - don't quote after a ":" as there's no need for it:
+//     undefined name: foo
+//   - don't quote if the name is used correctly in a statement:
+//     goto L jumps over variable declaration
+//
+// quote encloses s in `' quotes, as in `foo',
+// except for _ which is left alone.
+func quote(s string) string {
+	if s == "_" {
+		// `_' is ugly and not necessary
+		return s
+	}
+	return "`" + s + "'"
+}
+
 func sprintf(qf Qualifier, tpSubscripts bool, format string, args ...any) string {
 	for i, arg := range args {
 		switch a := arg.(type) {
diff --git a/src/cmd/compile/internal/types2/issues_test.go b/src/cmd/compile/internal/types2/issues_test.go
index 0275fe70d7..8c9dfb32f5 100644
--- a/src/cmd/compile/internal/types2/issues_test.go
+++ b/src/cmd/compile/internal/types2/issues_test.go
@@ -257,13 +257,12 @@ func TestIssue22525(t *testing.T) {
 	got := "\n"
 	conf := Config{Error: func(err error) { got += err.Error() + "\n" }}
 	typecheck(src, &conf, nil) // do not crash
-	want := `
-p:1:27: a declared and not used
-p:1:30: b declared and not used
-p:1:33: c declared and not used
-p:1:36: d declared and not used
-p:1:39: e declared and not used
-`
+	want := "\n" +
+		"p:1:27: `a' declared and not used\n" +
+		"p:1:30: `b' declared and not used\n" +
+		"p:1:33: `c' declared and not used\n" +
+		"p:1:36: `d' declared and not used\n" +
+		"p:1:39: `e' declared and not used\n"
 	if got != want {
 		t.Errorf("got: %swant: %s", got, want)
 	}
diff --git a/src/cmd/compile/internal/types2/labels.go b/src/cmd/compile/internal/types2/labels.go
index 8ea58ad0aa..61b3ca7511 100644
--- a/src/cmd/compile/internal/types2/labels.go
+++ b/src/cmd/compile/internal/types2/labels.go
@@ -28,9 +28,11 @@ func (check *Checker) labels(body *syntax.BlockStmt) {
 			msg = "goto %s jumps into block"
 			alt.(*Label).used = true // avoid another error
 			code = JumpIntoBlock
+			// don't quote name here because "goto L" matches the code
 		} else {
 			msg = "label %s not declared"
 			code = UndeclaredLabel
+			name = quote(name)
 		}
 		check.errorf(jmp.Label, code, msg, name)
 	}
@@ -39,7 +41,7 @@ func (check *Checker) labels(body *syntax.BlockStmt) {
 	for name, obj := range all.elems {
 		obj = resolve(name, obj)
 		if lbl := obj.(*Label); !lbl.used {
-			check.softErrorf(lbl.pos, UnusedLabel, "label %s declared and not used", lbl.name)
+			check.softErrorf(lbl.pos, UnusedLabel, "label %s declared and not used", quote(lbl.name))
 		}
 	}
 }
@@ -135,7 +137,7 @@ func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *syntax.Lab
 				if alt := all.Insert(lbl); alt != nil {
 					err := check.newError(DuplicateLabel)
 					err.soft = true
-					err.addf(lbl.pos, "label %s already declared", name)
+					err.addf(lbl.pos, "label %s already declared", quote(name))
 					err.addAltDecl(alt)
 					err.report()
 					// ok to continue
@@ -191,7 +193,7 @@ func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *syntax.Lab
 					}
 				}
 				if !valid {
-					check.errorf(s.Label, MisplacedLabel, "invalid break label %s", name)
+					check.errorf(s.Label, MisplacedLabel, "invalid break label %s", quote(name))
 					return
 				}
 
@@ -206,7 +208,7 @@ func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *syntax.Lab
 					}
 				}
 				if !valid {
-					check.errorf(s.Label, MisplacedLabel, "invalid continue label %s", name)
+					check.errorf(s.Label, MisplacedLabel, "invalid continue label %s", quote(name))
 					return
 				}
 
diff --git a/src/cmd/compile/internal/types2/stmt.go b/src/cmd/compile/internal/types2/stmt.go
index 1a6ec4ffc1..7fd7009e13 100644
--- a/src/cmd/compile/internal/types2/stmt.go
+++ b/src/cmd/compile/internal/types2/stmt.go
@@ -64,7 +64,7 @@ func (check *Checker) usage(scope *Scope) {
 		return cmpPos(unused[i].pos, unused[j].pos) < 0
 	})
 	for _, v := range unused {
-		check.softErrorf(v.pos, UnusedVar, "%s declared and not used", v.name)
+		check.softErrorf(v.pos, UnusedVar, "%s declared and not used", quote(v.name))
 	}
 
 	for _, scope := range scope.children {
@@ -496,7 +496,7 @@ func (check *Checker) stmt(ctxt stmtContext, s syntax.Stmt) {
 			for _, obj := range res.vars {
 				if alt := check.lookup(obj.name); alt != nil && alt != obj {
 					err := check.newError(OutOfScopeResult)
-					err.addf(s, "result parameter %s not in scope at return", obj.name)
+					err.addf(s, "result parameter %s not in scope at return", quote(obj.name))
 					err.addf(alt, "inner declaration of %s", obj)
 					err.report()
 					// ok to continue
diff --git a/src/cmd/compile/internal/types2/typeset.go b/src/cmd/compile/internal/types2/typeset.go
index 63dafadeb4..2ce586e7a7 100644
--- a/src/cmd/compile/internal/types2/typeset.go
+++ b/src/cmd/compile/internal/types2/typeset.go
@@ -226,8 +226,8 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 		case explicit:
 			if check != nil {
 				err := check.newError(DuplicateDecl)
-				err.addf(atPos(pos), "duplicate method %s", m.name)
-				err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", m.name)
+				err.addf(atPos(pos), "duplicate method %s", quote(m.name))
+				err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", quote(m.name))
 				err.report()
 			}
 		default:
@@ -240,8 +240,8 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 				check.later(func() {
 					if pos.IsKnown() && !check.allowVersion(atPos(pos), go1_14) || !Identical(m.typ, other.Type()) {
 						err := check.newError(DuplicateDecl)
-						err.addf(atPos(pos), "duplicate method %s", m.name)
-						err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", m.name)
+						err.addf(atPos(pos), "duplicate method %s", quote(m.name))
+						err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", quote(m.name))
 						err.report()
 					}
 				}).describef(atPos(pos), "duplicate method check for %s", m.name)
diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index be7c306a8d..c2037b26d6 100644
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -87,7 +87,7 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
 
 	switch obj := obj.(type) {
 	case *PkgName:
-		check.errorf(e, InvalidPkgUse, "use of package %s not in selector", obj.name)
+		check.errorf(e, InvalidPkgUse, "use of package %s not in selector", quote(obj.name))
 		return
 
 	case *Const:
@@ -109,7 +109,7 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
 
 	case *TypeName:
 		if !check.enableAlias && check.isBrokenAlias(obj) {
-			check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", obj.name)
+			check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", quote(obj.name))
 			return
 		}
 		x.mode = typexpr
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index 6519fa302a..2272335945 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -27,7 +27,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 	if hasDots(call) && id != _Append {
 		check.errorf(dddErrPos(call),
 			InvalidDotDotDot,
-			invalidOp+"invalid use of ... with built-in %s", bin.name)
+			invalidOp+"invalid use of ... with built-in %s", quote(bin.name))
 		check.use(argList...)
 		return
 	}
@@ -212,7 +212,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 				if id == _Len {
 					code = InvalidLen
 				}
-				check.errorf(x, code, invalidArg+"%s for %s", x, bin.name)
+				check.errorf(x, code, invalidArg+"%s for %s", x, quote(bin.name))
 			}
 			return
 		}
@@ -535,7 +535,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 	case _Max, _Min:
 		// max(x, ...)
 		// min(x, ...)
-		check.verifyVersionf(call.Fun, go1_21, bin.name)
+		check.verifyVersionf(call.Fun, go1_21, quote(bin.name))
 
 		op := token.LSS
 		if id == _Max {
@@ -578,7 +578,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		if x.mode != constant_ {
 			x.mode = value
 			// A value must not be untyped.
-			check.assignment(x, &emptyInterface, "argument to "+bin.name)
+			check.assignment(x, &emptyInterface, "argument to "+quote(bin.name))
 			if x.mode == invalid {
 				return
 			}
@@ -643,7 +643,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		if nargs > 0 {
 			params = make([]Type, nargs)
 			for i, a := range args {
-				check.assignment(a, nil, "argument to "+predeclaredFuncs[id].name)
+				check.assignment(a, nil, "argument to "+quote(predeclaredFuncs[id].name))
 				if a.mode == invalid {
 					return
 				}
@@ -994,7 +994,7 @@ func (check *Checker) applyTypeFunc(f func(Type) Type, x *operand, id builtinId)
 		default:
 			panic("unreachable")
 		}
-		check.softErrorf(x, code, "%s not supported as argument to %s for go1.18 (see go.dev/issue/50937)", x, predeclaredFuncs[id].name)
+		check.softErrorf(x, code, "%s not supported as argument to %s for go1.18 (see go.dev/issue/50937)", x, quote(predeclaredFuncs[id].name))
 
 		// Construct a suitable new type parameter for the result type.
 		// The type parameter is placed in the current package so export/import
diff --git a/src/go/types/call.go b/src/go/types/call.go
index b4f155a501..bee97a182b 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -722,7 +722,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr, def *TypeName, w
 					goto Error
 				}
 				if !exp.Exported() {
-					check.errorf(e.Sel, UnexportedName, "%s not exported by package %s", sel, pkg.name)
+					check.errorf(e.Sel, UnexportedName, "%s not exported by package %s", quote(sel), quote(pkg.name))
 					// ok to continue
 				}
 			}
diff --git a/src/go/types/check.go b/src/go/types/check.go
index 6da42e63f6..763be7714f 100644
--- a/src/go/types/check.go
+++ b/src/go/types/check.go
@@ -303,7 +303,7 @@ func (check *Checker) initFiles(files []*ast.File) {
 			check.files = append(check.files, file)
 
 		default:
-			check.errorf(atPos(file.Package), MismatchedPkgName, "package %s; expected %s", name, pkg.name)
+			check.errorf(atPos(file.Package), MismatchedPkgName, "package %s; expected %s", quote(name), quote(pkg.name))
 			// ignore this file
 		}
 	}
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 19472382af..7de27eeb56 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -825,7 +825,7 @@ func (check *Checker) checkFieldUniqueness(base *Named) {
 					// For historical consistency, we report the primary error on the
 					// method, and the alt decl on the field.
 					err := check.newError(DuplicateFieldAndMethod)
-					err.addf(alt, "field and method with the same name %s", fld.name)
+					err.addf(alt, "field and method with the same name %s", quote(fld.name))
 					err.addAltDecl(fld)
 					err.report()
 				}
diff --git a/src/go/types/format.go b/src/go/types/format.go
index 09e599c3c3..f5edb01449 100644
--- a/src/go/types/format.go
+++ b/src/go/types/format.go
@@ -15,6 +15,39 @@ import (
 	"strings"
 )
 
+// quote encloses s in `' quotes, as in `foo', except for _,
+// which is left alone.
+//
+// Use to prevent confusion when user supplied names alter the
+// meaning of an error message.
+//
+// For instance, report
+//
+//	duplicate method `wanted'
+//
+// rather than
+//
+//	duplicate method wanted
+//
+// Exceptions:
+//
+//   - don't quote _:
+//     `_' is ugly and not necessary
+//   - don't quote after a ":" as there's no need for it:
+//     undefined name: foo
+//   - don't quote if the name is used correctly in a statement:
+//     goto L jumps over variable declaration
+//
+// quote encloses s in `' quotes, as in `foo',
+// except for _ which is left alone.
+func quote(s string) string {
+	if s == "_" {
+		// `_' is ugly and not necessary
+		return s
+	}
+	return "`" + s + "'"
+}
+
 func sprintf(fset *token.FileSet, qf Qualifier, tpSubscripts bool, format string, args ...any) string {
 	for i, arg := range args {
 		switch a := arg.(type) {
diff --git a/src/go/types/issues_test.go b/src/go/types/issues_test.go
index 6f9d5978e7..4f4bf6f077 100644
--- a/src/go/types/issues_test.go
+++ b/src/go/types/issues_test.go
@@ -265,13 +265,12 @@ func TestIssue22525(t *testing.T) {
 	got := "\n"
 	conf := Config{Error: func(err error) { got += err.Error() + "\n" }}
 	typecheck(src, &conf, nil) // do not crash
-	want := `
-p:1:27: a declared and not used
-p:1:30: b declared and not used
-p:1:33: c declared and not used
-p:1:36: d declared and not used
-p:1:39: e declared and not used
-`
+	want := "\n" +
+		"p:1:27: `a' declared and not used\n" +
+		"p:1:30: `b' declared and not used\n" +
+		"p:1:33: `c' declared and not used\n" +
+		"p:1:36: `d' declared and not used\n" +
+		"p:1:39: `e' declared and not used\n"
 	if got != want {
 		t.Errorf("got: %swant: %s", got, want)
 	}
diff --git a/src/go/types/labels.go b/src/go/types/labels.go
index 04e84083b5..c3fd437c14 100644
--- a/src/go/types/labels.go
+++ b/src/go/types/labels.go
@@ -29,9 +29,11 @@ func (check *Checker) labels(body *ast.BlockStmt) {
 			msg = "goto %s jumps into block"
 			alt.(*Label).used = true // avoid another error
 			code = JumpIntoBlock
+			// don't quote name here because "goto L" matches the code
 		} else {
 			msg = "label %s not declared"
 			code = UndeclaredLabel
+			name = quote(name)
 		}
 		check.errorf(jmp.Label, code, msg, name)
 	}
@@ -40,7 +42,7 @@ func (check *Checker) labels(body *ast.BlockStmt) {
 	for name, obj := range all.elems {
 		obj = resolve(name, obj)
 		if lbl := obj.(*Label); !lbl.used {
-			check.softErrorf(lbl, UnusedLabel, "label %s declared and not used", lbl.name)
+			check.softErrorf(lbl, UnusedLabel, "label %s declared and not used", quote(lbl.name))
 		}
 	}
 }
@@ -140,7 +142,7 @@ func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *ast.Labele
 				if alt := all.Insert(lbl); alt != nil {
 					err := check.newError(DuplicateLabel)
 					err.soft = true
-					err.addf(lbl, "label %s already declared", name)
+					err.addf(lbl, "label %s already declared", quote(name))
 					err.addAltDecl(alt)
 					err.report()
 					// ok to continue
@@ -196,7 +198,7 @@ func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *ast.Labele
 					}
 				}
 				if !valid {
-					check.errorf(s.Label, MisplacedLabel, "invalid break label %s", name)
+					check.errorf(s.Label, MisplacedLabel, "invalid break label %s", quote(name))
 					return
 				}
 
@@ -211,7 +213,7 @@ func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *ast.Labele
 					}
 				}
 				if !valid {
-					check.errorf(s.Label, MisplacedLabel, "invalid continue label %s", name)
+					check.errorf(s.Label, MisplacedLabel, "invalid continue label %s", quote(name))
 					return
 				}
 
diff --git a/src/go/types/stmt.go b/src/go/types/stmt.go
index 4fd37a68f0..30b4948216 100644
--- a/src/go/types/stmt.go
+++ b/src/go/types/stmt.go
@@ -65,7 +65,7 @@ func (check *Checker) usage(scope *Scope) {
 		return cmpPos(unused[i].pos, unused[j].pos) < 0
 	})
 	for _, v := range unused {
-		check.softErrorf(v, UnusedVar, "%s declared and not used", v.name)
+		check.softErrorf(v, UnusedVar, "%s declared and not used", quote(v.name))
 	}
 
 	for _, scope := range scope.children {
@@ -515,7 +515,7 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			for _, obj := range res.vars {
 				if alt := check.lookup(obj.name); alt != nil && alt != obj {
 					err := check.newError(OutOfScopeResult)
-					err.addf(s, "result parameter %s not in scope at return", obj.name)
+					err.addf(s, "result parameter %s not in scope at return", quote(obj.name))
 					err.addf(alt, "inner declaration of %s", obj)
 					err.report()
 					// ok to continue
diff --git a/src/go/types/typeset.go b/src/go/types/typeset.go
index 2e2ebb30f7..84eb83fb5f 100644
--- a/src/go/types/typeset.go
+++ b/src/go/types/typeset.go
@@ -228,8 +228,8 @@ func computeInterfaceTypeSet(check *Checker, pos token.Pos, ityp *Interface) *_T
 		case explicit:
 			if check != nil {
 				err := check.newError(DuplicateDecl)
-				err.addf(atPos(pos), "duplicate method %s", m.name)
-				err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", m.name)
+				err.addf(atPos(pos), "duplicate method %s", quote(m.name))
+				err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", quote(m.name))
 				err.report()
 			}
 		default:
@@ -242,8 +242,8 @@ func computeInterfaceTypeSet(check *Checker, pos token.Pos, ityp *Interface) *_T
 				check.later(func() {
 					if pos.IsValid() && !check.allowVersion(atPos(pos), go1_14) || !Identical(m.typ, other.Type()) {
 						err := check.newError(DuplicateDecl)
-						err.addf(atPos(pos), "duplicate method %s", m.name)
-						err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", m.name)
+						err.addf(atPos(pos), "duplicate method %s", quote(m.name))
+						err.addf(atPos(mpos[other.(*Func)]), "other declaration of %s", quote(m.name))
 						err.report()
 					}
 				}).describef(atPos(pos), "duplicate method check for %s", m.name)
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 7179a2466c..79e4c0ab66 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -88,7 +88,7 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
 
 	switch obj := obj.(type) {
 	case *PkgName:
-		check.errorf(e, InvalidPkgUse, "use of package %s not in selector", obj.name)
+		check.errorf(e, InvalidPkgUse, "use of package %s not in selector", quote(obj.name))
 		return
 
 	case *Const:
@@ -110,7 +110,7 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
 
 	case *TypeName:
 		if !check.enableAlias && check.isBrokenAlias(obj) {
-			check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", obj.name)
+			check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", quote(obj.name))
 			return
 		}
 		x.mode = typexpr
diff --git a/src/internal/types/testdata/check/builtins0.go b/src/internal/types/testdata/check/builtins0.go
index 12d8fbfd0e..2bfece824e 100644
--- a/src/internal/types/testdata/check/builtins0.go
+++ b/src/internal/types/testdata/check/builtins0.go
@@ -100,7 +100,10 @@ func cap1() {
 
 	var s [][]byte
 	_ = cap(s)
-	_ = cap(s... /* ERROR "invalid use of ..." */ )
+	_ = cap(s... /* ERROR "invalid use of ... with built-in `cap'" */ )
+
+	var x int
+	_ = cap(x /* ERROR "invalid argument: x (variable of type int) for `cap'" */ )
 }
 
 func cap2() {
diff --git a/src/internal/types/testdata/check/decls0.go b/src/internal/types/testdata/check/decls0.go
index 0b99faab19..bec2b17ada 100644
--- a/src/internal/types/testdata/check/decls0.go
+++ b/src/internal/types/testdata/check/decls0.go
@@ -137,7 +137,7 @@ type (
 	}
 	I3 interface {
 		m1()
-		m1 /* ERROR "duplicate method" */ ()
+		m1 /* ERROR "duplicate method `m1'" */ ()
 	}
 	I4 interface {
 		m1(x, y, x /* ERROR "redeclared" */ float32)
diff --git a/src/internal/types/testdata/check/decls2/decls2a.go b/src/internal/types/testdata/check/decls2/decls2a.go
index c2fb421b96..f14b709dcf 100644
--- a/src/internal/types/testdata/check/decls2/decls2a.go
+++ b/src/internal/types/testdata/check/decls2/decls2a.go
@@ -16,7 +16,7 @@ type T1 struct{
 
 func (T1) m() {}
 func (T1) m /* ERROR "already declared" */ () {}
-func (x *T1) f /* ERROR "field and method" */ () {}
+func (x *T1) f /* ERROR "field and method with the same name `f'" */ () {}
 
 // Conflict between embedded field and method name,
 // with the embedded field being a basic type.
@@ -30,7 +30,7 @@ type T1c struct {
 	time.Time
 }
 
-func (T1c) Time /* ERROR "field and method" */ () int { return 0 }
+func (T1c) Time /* ERROR "field and method with the same name `Time'" */ () int { return 0 }
 
 // Disabled for now: LookupFieldOrMethod will find Pointer even though
 // it's double-declared (it would cost extra in the common case to verify
diff --git a/src/internal/types/testdata/check/go1_13.go b/src/internal/types/testdata/check/go1_13.go
index cc7861d616..3340124cfa 100644
--- a/src/internal/types/testdata/check/go1_13.go
+++ b/src/internal/types/testdata/check/go1_13.go
@@ -14,10 +14,10 @@ type I interface { m() }
 
 type _ interface {
 	m()
-	I // ERROR "duplicate method m"
+	I // ERROR "duplicate method `m'"
 }
 
 type _ interface {
 	I
-	I // ERROR "duplicate method m"
+	I // ERROR "duplicate method `m'"
 }
diff --git a/src/internal/types/testdata/check/importdecl0/importdecl0a.go b/src/internal/types/testdata/check/importdecl0/importdecl0a.go
index d514ae4cb7..b255c19375 100644
--- a/src/internal/types/testdata/check/importdecl0/importdecl0a.go
+++ b/src/internal/types/testdata/check/importdecl0/importdecl0a.go
@@ -32,7 +32,7 @@ import f2 "fmt"
 
 // reflect.flag must not be visible in this package
 type flag int
-type _ reflect.flag /* ERROR "not exported" */
+type _ reflect.flag /* ERROR "`flag' not exported by package `reflect'" */
 
 // imported package name may conflict with local objects
 type reflect /* ERROR "reflect already declared" */ int
diff --git a/src/internal/types/testdata/check/labels.go b/src/internal/types/testdata/check/labels.go
index 5948952fbe..0a59e9e2dc 100644
--- a/src/internal/types/testdata/check/labels.go
+++ b/src/internal/types/testdata/check/labels.go
@@ -10,23 +10,23 @@ package labels
 var x int
 
 func f0() {
-L1 /* ERROR "label L1 declared and not used" */ :
+L1 /* ERROR "label `L1' declared and not used" */ :
 	for {
 	}
-L2 /* ERROR "label L2 declared and not used" */ :
+L2 /* ERROR "label `L2' declared and not used" */ :
 	select {
 	}
-L3 /* ERROR "label L3 declared and not used" */ :
+L3 /* ERROR "label `L3' declared and not used" */ :
 	switch {
 	}
-L4 /* ERROR "label L4 declared and not used" */ :
+L4 /* ERROR "label `L4' declared and not used" */ :
 	if true {
 	}
-L5 /* ERROR "label L5 declared and not used" */ :
+L5 /* ERROR "label `L5' declared and not used" */ :
 	f0()
 L6:
 	f0()
-L6 /* ERROR "label L6 already declared" */ :
+L6 /* ERROR "label `L6' already declared" */ :
 	f0()
 	if x == 20 {
 		goto L6
@@ -35,7 +35,7 @@ L6 /* ERROR "label L6 already declared" */ :
 L7:
 	for {
 		break L7
-		break L8 /* ERROR "invalid break label L8" */
+		break L8 /* ERROR "invalid break label `L8'" */
 	}
 
 // A label must be directly associated with a switch, select, or
@@ -43,8 +43,8 @@ L7:
 
 L7a /* ERROR "declared and not used" */ : L7b:
 	for {
-		break L7a /* ERROR "invalid break label L7a" */
-		continue L7a /* ERROR "invalid continue label L7a" */
+		break L7a /* ERROR "invalid break label `L7a'" */
+		continue L7a /* ERROR "invalid continue label `L7a'" */
 		continue L7b
 	}
 
@@ -52,7 +52,7 @@ L8:
 	for {
 		if x == 21 {
 			continue L8
-			continue L7 /* ERROR "invalid continue label L7" */
+			continue L7 /* ERROR "invalid continue label `L7'" */
 		}
 	}
 
@@ -60,23 +60,23 @@ L9:
 	switch {
 	case true:
 		break L9
-	defalt /* ERROR "label defalt declared and not used" */ :
+	defalt /* ERROR "label `defalt' declared and not used" */ :
 	}
 
 L10:
 	select {
 	default:
 		break L10
-		break L9 /* ERROR "invalid break label L9" */
+		break L9 /* ERROR "invalid break label `L9'" */
 	}
 
 	goto L10a
 L10a: L10b:
 	select {
 	default:
-		break L10a /* ERROR "invalid break label L10a" */
+		break L10a /* ERROR "invalid break label `L10a'" */
 		break L10b
-		continue L10b /* ERROR "invalid continue label L10b" */
+		continue L10b /* ERROR "invalid continue label `L10b'" */
 	}
 }
 
@@ -99,7 +99,7 @@ L2:
 			break L2
 		}
 		if x == 1 {
-			continue L2 /* ERROR "invalid continue label L2" */
+			continue L2 /* ERROR "invalid continue label `L2'" */
 		}
 		goto L2
 	}
@@ -111,7 +111,7 @@ L3:
 			break L3
 		}
 		if x == 12 {
-			continue L3 /* ERROR "invalid continue label L3" */
+			continue L3 /* ERROR "invalid continue label `L3'" */
 		}
 		goto L3
 	}
@@ -119,10 +119,10 @@ L3:
 L4:
 	if true {
 		if x == 13 {
-			break L4 /* ERROR "invalid break label L4" */
+			break L4 /* ERROR "invalid break label `L4'" */
 		}
 		if x == 14 {
-			continue L4 /* ERROR "invalid continue label L4" */
+			continue L4 /* ERROR "invalid continue label `L4'" */
 		}
 		if x == 15 {
 			goto L4
@@ -132,10 +132,10 @@ L4:
 L5:
 	f1()
 	if x == 16 {
-		break L5 /* ERROR "invalid break label L5" */
+		break L5 /* ERROR "invalid break label `L5'" */
 	}
 	if x == 17 {
-		continue L5 /* ERROR "invalid continue label L5" */
+		continue L5 /* ERROR "invalid continue label `L5'" */
 	}
 	if x == 18 {
 		goto L5
@@ -143,10 +143,10 @@ L5:
 
 	for {
 		if x == 19 {
-			break L1 /* ERROR "invalid break label L1" */
+			break L1 /* ERROR "invalid break label `L1'" */
 		}
 		if x == 20 {
-			continue L1 /* ERROR "invalid continue label L1" */
+			continue L1 /* ERROR "invalid continue label `L1'" */
 		}
 		if x == 21 {
 			goto L1
@@ -157,10 +157,10 @@ L5:
 // Additional tests not in the original files.
 
 func f2() {
-L1 /* ERROR "label L1 declared and not used" */ :
+L1 /* ERROR "label `L1' declared and not used" */ :
 	if x == 0 {
 		for {
-			continue L1 /* ERROR "invalid continue label L1" */
+			continue L1 /* ERROR "invalid continue label `L1'" */
 		}
 	}
 }
@@ -170,11 +170,11 @@ L1:
 L2:
 L3:
 	for {
-		break L1 /* ERROR "invalid break label L1" */
-		break L2 /* ERROR "invalid break label L2" */
+		break L1 /* ERROR "invalid break label `L1'" */
+		break L2 /* ERROR "invalid break label `L2'" */
 		break L3
-		continue L1 /* ERROR "invalid continue label L1" */
-		continue L2 /* ERROR "invalid continue label L2" */
+		continue L1 /* ERROR "invalid continue label `L1'" */
+		continue L2 /* ERROR "invalid continue label `L2'" */
 		continue L3
 		goto L1
 		goto L2
diff --git a/src/internal/types/testdata/check/stmt0.go b/src/internal/types/testdata/check/stmt0.go
index b61f1c7232..a6c47cb483 100644
--- a/src/internal/types/testdata/check/stmt0.go
+++ b/src/internal/types/testdata/check/stmt0.go
@@ -222,7 +222,7 @@ func selects() {
 	ch2 := make(chan int)
 	select {
 	case <-ch1:
-		var ch2 /* ERROR "ch2 declared and not used" */ chan bool
+		var ch2 /* ERROR "`ch2' declared and not used" */ chan bool
 	case i := <-ch2:
 		print(i + 1)
 	}
@@ -394,7 +394,7 @@ func returns2() (a, b int) {
 	{
 		type a int
 		return 1, 2
-		return /* ERROR "a not in scope at return" */
+		return /* ERROR "`a' not in scope at return" */
 	}
 }
 
diff --git a/src/internal/types/testdata/fixedbugs/issue50779.go b/src/internal/types/testdata/fixedbugs/issue50779.go
index 59c0f2d6a0..a0a126dff0 100644
--- a/src/internal/types/testdata/fixedbugs/issue50779.go
+++ b/src/internal/types/testdata/fixedbugs/issue50779.go
@@ -17,7 +17,7 @@ type R[S any, P any] struct{}
 type SR = R[SS, ST]
 
 type SS interface {
-	NSR(any) *SR // ERROR "invalid use of type alias SR in recursive type"
+	NSR(any) *SR // ERROR "invalid use of type alias `SR' in recursive type"
 }
 
 type C interface {
diff --git a/src/internal/types/testdata/fixedbugs/issue66285.go b/src/internal/types/testdata/fixedbugs/issue66285.go
index 9811fec3f3..2e8bb59508 100644
--- a/src/internal/types/testdata/fixedbugs/issue66285.go
+++ b/src/internal/types/testdata/fixedbugs/issue66285.go
@@ -19,7 +19,7 @@ import "io"
 
 type _ interface {
 	Reader
-	Reader // ERROR "duplicate method Read"
+	Reader // ERROR "duplicate method `Read'"
 }
 
 type Reader interface {
@@ -28,10 +28,10 @@ type Reader interface {
 
 type _ interface {
 	io.Reader
-	Reader // ERROR "duplicate method Read"
+	Reader // ERROR "duplicate method `Read'"
 }
 
 type _ interface {
 	io.Reader
-	io /* ERROR "duplicate method Read" */ .Reader
+	io /* ERROR "duplicate method `Read'" */ .Reader
 }