go/types, types2: remove unreachable func (minor cleanup)

In some places we can't use unreachable() because it does
not terminate control flow and we need to resort to panic.
Be consistent and just use panic("unreachable") everywhere.
This also opens the door to reporting more specific panic
messages.

Mechanical change: s/unreachable()/panic("unreachable")/

Minor cleanup for better consistency.

Change-Id: I6b52af7c21dcfaa1ca19839d14040552db5d4cb4
Reviewed-on: https://go-review.googlesource.com/c/go/+/566135
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

38 files changed, 69 insertions, 77 deletions

diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index 79ed6ad640..a87474ad6c 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -908,7 +908,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		// trace is only available in test mode - no need to record signature
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	assert(x.mode != invalid)
@@ -947,7 +947,7 @@ func hasVarSize(t Type, seen map[*Named]bool) (varSized bool) {
 	case *Interface:
 		return isTypeParam(t)
 	case *Named, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	return false
 }
@@ -990,7 +990,7 @@ func (check *Checker) applyTypeFunc(f func(Type) Type, x *operand, id builtinId)
 		case _Complex:
 			code = InvalidComplex
 		default:
-			unreachable()
+			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)
 
diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 7e4cf8974f..55400d436c 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -757,7 +757,7 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr, def *TypeName
 				x.id = exp.id
 			default:
 				check.dump("%v: unexpected object %v", atPos(e.Sel), exp)
-				unreachable()
+				panic("unreachable")
 			}
 			x.expr = e
 			return
@@ -910,7 +910,7 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr, def *TypeName
 			check.addDeclDep(obj)
 
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
diff --git a/src/cmd/compile/internal/types2/check.go b/src/cmd/compile/internal/types2/check.go
index 0582367083..8c2bac2850 100644
--- a/src/cmd/compile/internal/types2/check.go
+++ b/src/cmd/compile/internal/types2/check.go
@@ -513,7 +513,7 @@ func (check *Checker) recordUntyped() {
 	for x, info := range check.untyped {
 		if debug && isTyped(info.typ) {
 			check.dump("%v: %s (type %s) is typed", atPos(x), x, info.typ)
-			unreachable()
+			panic("unreachable")
 		}
 		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
 	}
@@ -578,7 +578,7 @@ func (check *Checker) recordBuiltinType(f syntax.Expr, sig *Signature) {
 		case *syntax.ParenExpr:
 			f = p.X
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 }
diff --git a/src/cmd/compile/internal/types2/const.go b/src/cmd/compile/internal/types2/const.go
index af27c727dd..5e5bc74ba3 100644
--- a/src/cmd/compile/internal/types2/const.go
+++ b/src/cmd/compile/internal/types2/const.go
@@ -118,7 +118,7 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 			case Uint64:
 				return 0 <= x
 			default:
-				unreachable()
+				panic("unreachable")
 			}
 		}
 		// x does not fit into int64
@@ -159,7 +159,7 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 		case UntypedFloat:
 			return true
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 
 	case isComplex(typ):
@@ -191,7 +191,7 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 		case UntypedComplex:
 			return true
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 
 	case isString(typ):
diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index f3e3418f4f..4408a0b168 100644
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -162,7 +162,7 @@ func (check *Checker) objDecl(obj Object, def *TypeName) {
 			}
 
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 		assert(obj.Type() != nil)
 		return
@@ -171,7 +171,7 @@ func (check *Checker) objDecl(obj Object, def *TypeName) {
 	d := check.objMap[obj]
 	if d == nil {
 		check.dump("%v: %s should have been declared", obj.Pos(), obj)
-		unreachable()
+		panic("unreachable")
 	}
 
 	// save/restore current environment and set up object environment
@@ -202,7 +202,7 @@ func (check *Checker) objDecl(obj Object, def *TypeName) {
 		// functions may be recursive - no need to track dependencies
 		check.funcDecl(obj, d)
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 }
 
@@ -216,7 +216,7 @@ func (check *Checker) validCycle(obj Object) (valid bool) {
 		isPkgObj := obj.Parent() == check.pkg.scope
 		if isPkgObj != inObjMap {
 			check.dump("%v: inconsistent object map for %s (isPkgObj = %v, inObjMap = %v)", obj.Pos(), obj, isPkgObj, inObjMap)
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
@@ -266,7 +266,7 @@ loop:
 		case *Func:
 			// ignored for now
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
diff --git a/src/cmd/compile/internal/types2/errors.go b/src/cmd/compile/internal/types2/errors.go
index 4326ca67ef..e7d8863c6f 100644
--- a/src/cmd/compile/internal/types2/errors.go
+++ b/src/cmd/compile/internal/types2/errors.go
@@ -28,10 +28,6 @@ func assert(p bool) {
 	}
 }
 
-func unreachable() {
-	panic("unreachable")
-}
-
 // An error_ represents a type-checking error.
 // To report an error_, call Checker.report.
 type error_ struct {
diff --git a/src/cmd/compile/internal/types2/expr.go b/src/cmd/compile/internal/types2/expr.go
index d7d60cc73c..ca499a17a9 100644
--- a/src/cmd/compile/internal/types2/expr.go
+++ b/src/cmd/compile/internal/types2/expr.go
@@ -268,7 +268,7 @@ func (check *Checker) updateExprType0(parent, x syntax.Expr, typ Type, final boo
 		// upon assignment or use.
 		if debug {
 			check.dump("%v: found old type(%s): %s (new: %s)", atPos(x), x, old.typ, typ)
-			unreachable()
+			panic("unreachable")
 		}
 		return
 
@@ -337,7 +337,7 @@ func (check *Checker) updateExprType0(parent, x syntax.Expr, typ Type, final boo
 		}
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	// If the new type is not final and still untyped, just
@@ -546,7 +546,7 @@ func (check *Checker) comparison(x, y *operand, op syntax.Operator, switchCase b
 		}
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	// comparison is ok
@@ -1042,7 +1042,7 @@ func (check *Checker) exprInternal(T *target, x *operand, e syntax.Expr, hint Ty
 
 	switch e := e.(type) {
 	case nil:
-		unreachable()
+		panic("unreachable")
 
 	case *syntax.BadExpr:
 		goto Error // error was reported before
@@ -1654,7 +1654,7 @@ func (check *Checker) exclude(x *operand, modeset uint) {
 			msg = "%s is not an expression"
 			code = NotAnExpr
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 		check.errorf(x, code, msg, x)
 		x.mode = invalid
diff --git a/src/cmd/compile/internal/types2/gcsizes.go b/src/cmd/compile/internal/types2/gcsizes.go
index d204d9feef..15f3e00642 100644
--- a/src/cmd/compile/internal/types2/gcsizes.go
+++ b/src/cmd/compile/internal/types2/gcsizes.go
@@ -56,7 +56,7 @@ func (s *gcSizes) Alignof(T Type) (result int64) {
 			return s.WordSize
 		}
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	a := s.Sizeof(T) // may be 0 or negative
 	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
@@ -154,7 +154,7 @@ func (s *gcSizes) Sizeof(T Type) int64 {
 		assert(!isTypeParam(T))
 		return s.WordSize * 2
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	return s.WordSize // catch-all
 }
diff --git a/src/cmd/compile/internal/types2/lookup.go b/src/cmd/compile/internal/types2/lookup.go
index 5aa8091a5c..3583a48407 100644
--- a/src/cmd/compile/internal/types2/lookup.go
+++ b/src/cmd/compile/internal/types2/lookup.go
@@ -472,7 +472,7 @@ func (check *Checker) missingMethod(V, T Type, static bool, equivalent func(x, y
 		case field:
 			*cause = check.sprintf("(%s.%s is a field, not a method)", V, m.Name())
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
diff --git a/src/cmd/compile/internal/types2/operand.go b/src/cmd/compile/internal/types2/operand.go
index 193231794f..15ec86fb5e 100644
--- a/src/cmd/compile/internal/types2/operand.go
+++ b/src/cmd/compile/internal/types2/operand.go
@@ -226,7 +226,7 @@ func (x *operand) setConst(k syntax.LitKind, lit string) {
 	case syntax.StringLit:
 		kind = UntypedString
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	val := makeFromLiteral(lit, k)
diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index bb2b53a942..938f8dcf8b 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -477,7 +477,7 @@ func (c *comparer) identical(x, y Type, p *ifacePair) bool {
 		// avoid a crash in case of nil type
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	return false
diff --git a/src/cmd/compile/internal/types2/return.go b/src/cmd/compile/internal/types2/return.go
index 01988b012e..4e9988755c 100644
--- a/src/cmd/compile/internal/types2/return.go
+++ b/src/cmd/compile/internal/types2/return.go
@@ -16,7 +16,7 @@ import (
 func (check *Checker) isTerminating(s syntax.Stmt, label string) bool {
 	switch s := s.(type) {
 	default:
-		unreachable()
+		panic("unreachable")
 
 	case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.SendStmt,
 		*syntax.AssignStmt, *syntax.CallStmt:
@@ -108,7 +108,7 @@ func (check *Checker) isTerminatingSwitch(body []*syntax.CaseClause, label strin
 func hasBreak(s syntax.Stmt, label string, implicit bool) bool {
 	switch s := s.(type) {
 	default:
-		unreachable()
+		panic("unreachable")
 
 	case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.ExprStmt,
 		*syntax.SendStmt, *syntax.AssignStmt, *syntax.CallStmt,
diff --git a/src/cmd/compile/internal/types2/selection.go b/src/cmd/compile/internal/types2/selection.go
index dfbf3a0191..2d882b2ee4 100644
--- a/src/cmd/compile/internal/types2/selection.go
+++ b/src/cmd/compile/internal/types2/selection.go
@@ -163,7 +163,7 @@ func SelectionString(s *Selection, qf Qualifier) string {
 	case MethodExpr:
 		k = "method expr "
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 	var buf bytes.Buffer
 	buf.WriteString(k)
diff --git a/src/cmd/compile/internal/types2/signature.go b/src/cmd/compile/internal/types2/signature.go
index 18a64ec1a0..72b57bc842 100644
--- a/src/cmd/compile/internal/types2/signature.go
+++ b/src/cmd/compile/internal/types2/signature.go
@@ -247,7 +247,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []
 				case *TypeParam:
 					// The underlying type of a receiver base type cannot be a
 					// type parameter: "type T[P any] P" is not a valid declaration.
-					unreachable()
+					panic("unreachable")
 				}
 				if cause != "" {
 					check.errorf(recv, InvalidRecv, "invalid receiver type %s (%s)", rtyp, cause)
diff --git a/src/cmd/compile/internal/types2/sizes.go b/src/cmd/compile/internal/types2/sizes.go
index 486c05c61c..7d20c97010 100644
--- a/src/cmd/compile/internal/types2/sizes.go
+++ b/src/cmd/compile/internal/types2/sizes.go
@@ -94,7 +94,7 @@ func (s *StdSizes) Alignof(T Type) (result int64) {
 			return s.WordSize
 		}
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	a := s.Sizeof(T) // may be 0 or negative
 	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
@@ -221,7 +221,7 @@ func (s *StdSizes) Sizeof(T Type) int64 {
 		assert(!isTypeParam(T))
 		return s.WordSize * 2
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	return s.WordSize // catch-all
 }
diff --git a/src/cmd/compile/internal/types2/stmt.go b/src/cmd/compile/internal/types2/stmt.go
index 272636ff39..0ec5829ee4 100644
--- a/src/cmd/compile/internal/types2/stmt.go
+++ b/src/cmd/compile/internal/types2/stmt.go
@@ -186,7 +186,7 @@ func (check *Checker) suspendedCall(keyword string, call syntax.Expr) {
 	case statement:
 		return
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 	check.errorf(&x, code, "%s %s %s", keyword, msg, &x)
 }
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 1ad73c41ce..fa636a1e1e 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -283,7 +283,7 @@ func (subst *subster) typ(typ Type) Type {
 		return subst.smap.lookup(t)
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	return typ
diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index d131306a14..be7c306a8d 100644
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -139,7 +139,7 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
 		x.mode = nilvalue
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	x.typ = typ
diff --git a/src/cmd/compile/internal/types2/universe.go b/src/cmd/compile/internal/types2/universe.go
index c8be81b9eb..8e1e4a2bb7 100644
--- a/src/cmd/compile/internal/types2/universe.go
+++ b/src/cmd/compile/internal/types2/universe.go
@@ -279,7 +279,7 @@ func def(obj Object) {
 		case *Builtin:
 			obj.pkg = Unsafe
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 	if scope.Insert(obj) != nil {
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index 040b24f5cc..6519fa302a 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -910,7 +910,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		// trace is only available in test mode - no need to record signature
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	assert(x.mode != invalid)
@@ -949,7 +949,7 @@ func hasVarSize(t Type, seen map[*Named]bool) (varSized bool) {
 	case *Interface:
 		return isTypeParam(t)
 	case *Named, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	return false
 }
@@ -992,7 +992,7 @@ func (check *Checker) applyTypeFunc(f func(Type) Type, x *operand, id builtinId)
 		case _Complex:
 			code = InvalidComplex
 		default:
-			unreachable()
+			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)
 
diff --git a/src/go/types/call.go b/src/go/types/call.go
index dcd833d23c..b7775f6c6b 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -758,7 +758,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr, def *TypeName, w
 				x.id = exp.id
 			default:
 				check.dump("%v: unexpected object %v", e.Sel.Pos(), exp)
-				unreachable()
+				panic("unreachable")
 			}
 			x.expr = e
 			return
@@ -957,7 +957,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr, def *TypeName, w
 			check.addDeclDep(obj)
 
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
diff --git a/src/go/types/check.go b/src/go/types/check.go
index 1e2ca59392..be992215d1 100644
--- a/src/go/types/check.go
+++ b/src/go/types/check.go
@@ -518,7 +518,7 @@ func (check *Checker) recordUntyped() {
 	for x, info := range check.untyped {
 		if debug && isTyped(info.typ) {
 			check.dump("%v: %s (type %s) is typed", x.Pos(), x, info.typ)
-			unreachable()
+			panic("unreachable")
 		}
 		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
 	}
@@ -554,7 +554,7 @@ func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
 		case *ast.ParenExpr:
 			f = p.X
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 }
diff --git a/src/go/types/const.go b/src/go/types/const.go
index bffea146a0..4956d12883 100644
--- a/src/go/types/const.go
+++ b/src/go/types/const.go
@@ -119,7 +119,7 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 			case Uint64:
 				return 0 <= x
 			default:
-				unreachable()
+				panic("unreachable")
 			}
 		}
 		// x does not fit into int64
@@ -160,7 +160,7 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 		case UntypedFloat:
 			return true
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 
 	case isComplex(typ):
@@ -192,7 +192,7 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 		case UntypedComplex:
 			return true
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 
 	case isString(typ):
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 9f8c44ab50..3994d1650f 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -160,7 +160,7 @@ func (check *Checker) objDecl(obj Object, def *TypeName) {
 			}
 
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 		assert(obj.Type() != nil)
 		return
@@ -169,7 +169,7 @@ func (check *Checker) objDecl(obj Object, def *TypeName) {
 	d := check.objMap[obj]
 	if d == nil {
 		check.dump("%v: %s should have been declared", obj.Pos(), obj)
-		unreachable()
+		panic("unreachable")
 	}
 
 	// save/restore current environment and set up object environment
@@ -200,7 +200,7 @@ func (check *Checker) objDecl(obj Object, def *TypeName) {
 		// functions may be recursive - no need to track dependencies
 		check.funcDecl(obj, d)
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 }
 
@@ -214,7 +214,7 @@ func (check *Checker) validCycle(obj Object) (valid bool) {
 		isPkgObj := obj.Parent() == check.pkg.scope
 		if isPkgObj != inObjMap {
 			check.dump("%v: inconsistent object map for %s (isPkgObj = %v, inObjMap = %v)", obj.Pos(), obj, isPkgObj, inObjMap)
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
@@ -264,7 +264,7 @@ loop:
 		case *Func:
 			// ignored for now
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
diff --git a/src/go/types/errors.go b/src/go/types/errors.go
index 0345cf7844..0e4b8a8c44 100644
--- a/src/go/types/errors.go
+++ b/src/go/types/errors.go
@@ -29,10 +29,6 @@ func assert(p bool) {
 	}
 }
 
-func unreachable() {
-	panic("unreachable")
-}
-
 // An error_ represents a type-checking error.
 // To report an error_, call Checker.report.
 type error_ struct {
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 927cb50d40..626dd0e775 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -255,7 +255,7 @@ func (check *Checker) updateExprType0(parent, x ast.Expr, typ Type, final bool)
 		// upon assignment or use.
 		if debug {
 			check.dump("%v: found old type(%s): %s (new: %s)", x.Pos(), x, old.typ, typ)
-			unreachable()
+			panic("unreachable")
 		}
 		return
 
@@ -301,7 +301,7 @@ func (check *Checker) updateExprType0(parent, x ast.Expr, typ Type, final bool)
 		}
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	// If the new type is not final and still untyped, just
@@ -524,7 +524,7 @@ func (check *Checker) comparison(x, y *operand, op token.Token, switchCase bool)
 		}
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	// comparison is ok
@@ -1601,7 +1601,7 @@ func (check *Checker) exclude(x *operand, modeset uint) {
 			msg = "%s is not an expression"
 			code = NotAnExpr
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 		check.errorf(x, code, msg, x)
 		x.mode = invalid
diff --git a/src/go/types/gcsizes.go b/src/go/types/gcsizes.go
index 4329cc22e8..99ab95fb90 100644
--- a/src/go/types/gcsizes.go
+++ b/src/go/types/gcsizes.go
@@ -58,7 +58,7 @@ func (s *gcSizes) Alignof(T Type) (result int64) {
 			return s.WordSize
 		}
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	a := s.Sizeof(T) // may be 0 or negative
 	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
@@ -156,7 +156,7 @@ func (s *gcSizes) Sizeof(T Type) int64 {
 		assert(!isTypeParam(T))
 		return s.WordSize * 2
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	return s.WordSize // catch-all
 }
diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index 436a7afbaa..68bfd885dc 100644
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -474,7 +474,7 @@ func (check *Checker) missingMethod(V, T Type, static bool, equivalent func(x, y
 		case field:
 			*cause = check.sprintf("(%s.%s is a field, not a method)", V, m.Name())
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 
diff --git a/src/go/types/operand.go b/src/go/types/operand.go
index e922ca5cc3..883ee62394 100644
--- a/src/go/types/operand.go
+++ b/src/go/types/operand.go
@@ -229,7 +229,7 @@ func (x *operand) setConst(k token.Token, lit string) {
 	case token.STRING:
 		kind = UntypedString
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	val := makeFromLiteral(lit, k)
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 677dff01a0..e1a32143f1 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -479,7 +479,7 @@ func (c *comparer) identical(x, y Type, p *ifacePair) bool {
 		// avoid a crash in case of nil type
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	return false
diff --git a/src/go/types/return.go b/src/go/types/return.go
index 95318e9002..91bd95b6e0 100644
--- a/src/go/types/return.go
+++ b/src/go/types/return.go
@@ -17,7 +17,7 @@ import (
 func (check *Checker) isTerminating(s ast.Stmt, label string) bool {
 	switch s := s.(type) {
 	default:
-		unreachable()
+		panic("unreachable")
 
 	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.SendStmt,
 		*ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt, *ast.DeferStmt,
@@ -110,7 +110,7 @@ func (check *Checker) isTerminatingSwitch(body *ast.BlockStmt, label string) boo
 func hasBreak(s ast.Stmt, label string, implicit bool) bool {
 	switch s := s.(type) {
 	default:
-		unreachable()
+		panic("unreachable")
 
 	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.ExprStmt,
 		*ast.SendStmt, *ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt,
diff --git a/src/go/types/selection.go b/src/go/types/selection.go
index 50d340c738..18d3204fb1 100644
--- a/src/go/types/selection.go
+++ b/src/go/types/selection.go
@@ -165,7 +165,7 @@ func SelectionString(s *Selection, qf Qualifier) string {
 	case MethodExpr:
 		k = "method expr "
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 	var buf bytes.Buffer
 	buf.WriteString(k)
diff --git a/src/go/types/signature.go b/src/go/types/signature.go
index cad42cb942..8d26a8776d 100644
--- a/src/go/types/signature.go
+++ b/src/go/types/signature.go
@@ -251,7 +251,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 				case *TypeParam:
 					// The underlying type of a receiver base type cannot be a
 					// type parameter: "type T[P any] P" is not a valid declaration.
-					unreachable()
+					panic("unreachable")
 				}
 				if cause != "" {
 					check.errorf(recv, InvalidRecv, "invalid receiver type %s (%s)", rtyp, cause)
diff --git a/src/go/types/sizes.go b/src/go/types/sizes.go
index 12a21401e2..b7a2bea0e8 100644
--- a/src/go/types/sizes.go
+++ b/src/go/types/sizes.go
@@ -96,7 +96,7 @@ func (s *StdSizes) Alignof(T Type) (result int64) {
 			return s.WordSize
 		}
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	a := s.Sizeof(T) // may be 0 or negative
 	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
@@ -223,7 +223,7 @@ func (s *StdSizes) Sizeof(T Type) int64 {
 		assert(!isTypeParam(T))
 		return s.WordSize * 2
 	case *TypeParam, *Union:
-		unreachable()
+		panic("unreachable")
 	}
 	return s.WordSize // catch-all
 }
diff --git a/src/go/types/stmt.go b/src/go/types/stmt.go
index f16e288ffc..ca528368b5 100644
--- a/src/go/types/stmt.go
+++ b/src/go/types/stmt.go
@@ -183,7 +183,7 @@ func (check *Checker) suspendedCall(keyword string, call *ast.CallExpr) {
 	case statement:
 		return
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 	check.errorf(&x, code, "%s %s %s", keyword, msg, &x)
 }
diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index 178f717283..00796ac924 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -285,7 +285,7 @@ func (subst *subster) typ(typ Type) Type {
 		return subst.smap.lookup(t)
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	return typ
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index afb94b9026..7179a2466c 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -140,7 +140,7 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
 		x.mode = value
 
 	default:
-		unreachable()
+		panic("unreachable")
 	}
 
 	x.typ = typ
diff --git a/src/go/types/universe.go b/src/go/types/universe.go
index bde0293527..8154d29053 100644
--- a/src/go/types/universe.go
+++ b/src/go/types/universe.go
@@ -281,7 +281,7 @@ func def(obj Object) {
 		case *Builtin:
 			obj.pkg = Unsafe
 		default:
-			unreachable()
+			panic("unreachable")
 		}
 	}
 	if scope.Insert(obj) != nil {