go/types, types2: fix printing of error message with variadic calls

Distinguish between variadic signatures and argument lists to
(possibly variadic) functions and place `...` before or after
the last type in the list of types.

Fixes a panic.

Fixes #70526.

Change-Id: I77aba8f50984a21ebcdb62582030f2d0fe0eb097
Reviewed-on: https://go-review.googlesource.com/c/go/+/632275
Reviewed-by: Alan Donovan <[email protected]>
Auto-Submit: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: griesemer

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

@@ -295,7 +295,11 @@ func varTypes(list []*Var) (res []Type) {
 // ti's are user-friendly string representations for the given types.
 // If variadic is set and the last type is a slice, its string is of
 // the form "...E" where E is the slice's element type.
-func (check *Checker) typesSummary(list []Type, variadic bool) string {
+// If hasDots is set, the last argument string is of the form "T..."
+// where T is the last type.
+// Only one of variadic and hasDots may be set.
+func (check *Checker) typesSummary(list []Type, variadic, hasDots bool) string {
+	assert(!(variadic && hasDots))
 	var res []string
 	for i, t := range list {
 		var s string
@@ -304,7 +308,7 @@ func (check *Checker) typesSummary(list []Type, variadic bool) string {
 			fallthrough // should not happen but be cautious
 		case !isValid(t):
 			s = "unknown type"
-		case isUntyped(t):
+		case isUntyped(t): // => *Basic
 			if isNumeric(t) {
 				// Do not imply a specific type requirement:
 				// "have number, want float64" is better than
@@ -316,12 +320,22 @@ func (check *Checker) typesSummary(list []Type, variadic bool) string {
 				// for compactness.
 				s = strings.Replace(t.(*Basic).name, "untyped ", "", -1)
 			}
-		case variadic && i == len(list)-1:
-			s = check.sprintf("...%s", t.(*Slice).elem)
-		}
-		if s == "" {
+		default:
 			s = check.sprintf("%s", t)
 		}
+		// handle ... parameters/arguments
+		if i == len(list)-1 {
+			switch {
+			case variadic:
+				// In correct code, the parameter type is a slice, but be careful.
+				if t, _ := t.(*Slice); t != nil {
+					s = check.sprintf("%s", t.elem)
+				}
+				s = "..." + s
+			case hasDots:
+				s += "..."
+			}
+		}
 		res = append(res, s)
 	}
 	return "(" + strings.Join(res, ", ") + ")"
@@ -359,8 +373,8 @@ func (check *Checker) returnError(at poser, lhs []*Var, rhs []*operand) {
 	}
 	err := check.newError(WrongResultCount)
 	err.addf(at, "%s return values", qualifier)
-	err.addf(nopos, "have %s", check.typesSummary(operandTypes(rhs), false))
-	err.addf(nopos, "want %s", check.typesSummary(varTypes(lhs), false))
+	err.addf(nopos, "have %s", check.typesSummary(operandTypes(rhs), false, false))
+	err.addf(nopos, "want %s", check.typesSummary(varTypes(lhs), false, false))
 	err.report()
 }
 

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

@@ -530,8 +530,8 @@ func (check *Checker) arguments(call *syntax.CallExpr, sig *Signature, targs []T
 		}
 		err := check.newError(WrongArgCount)
 		err.addf(at, "%s arguments in call to %s", qualifier, call.Fun)
-		err.addf(nopos, "have %s", check.typesSummary(operandTypes(args), ddd))
-		err.addf(nopos, "want %s", check.typesSummary(varTypes(params), sig.variadic))
+		err.addf(nopos, "have %s", check.typesSummary(operandTypes(args), false, ddd))
+		err.addf(nopos, "want %s", check.typesSummary(varTypes(params), sig.variadic, false))
 		err.report()
 		return
 	}

src/go/types/assignments.go

@@ -530,8 +530,8 @@ func (check *Checker) arguments(call *ast.CallExpr, sig *Signature, targs []Type
 		}
 		err := check.newError(WrongArgCount)
 		err.addf(at, "%s arguments in call to %s", qualifier, call.Fun)
-		err.addf(noposn, "have %s", check.typesSummary(operandTypes(args), ddd))
-		err.addf(noposn, "want %s", check.typesSummary(varTypes(params), sig.variadic))
+		err.addf(noposn, "have %s", check.typesSummary(operandTypes(args), false, ddd))
+		err.addf(noposn, "want %s", check.typesSummary(varTypes(params), sig.variadic, false))
 		err.report()
 		return
 	}

src/go/types/call.go

@@ -7,8 +7,8 @@ package p
 func _() {
 	var values []int
 	vf(values /* ERROR "(variable of type []int) as string value" */)
-	vf(values...) /* ERROR "have (...int)" */
-	vf("ab", "cd", values /* ERROR "have (string, string, ...int)" */ ...)
+	vf(values...) /* ERROR "have ([]int...)\n\twant (string, ...int)" */
+	vf("ab", "cd", values /* ERROR "have (string, string, []int...)\n\twant (string, ...int)" */ ...)
 }
 
 func vf(method string, values ...int) {

src/internal/types/testdata/fixedbugs/issue70150.go

@@ -0,0 +1,13 @@
+// Copyright 2024 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 f(...any)
+
+func _(x int, s []int) {
+	f(0, x /* ERROR "have (number, int...)\n\twant (...any)" */ ...)
+	f(0, s /* ERROR "have (number, []int...)\n\twant (...any)" */ ...)
+	f(0, 0 /* ERROR "have (number, number...)\n\twant (...any)" */ ...)
+}