go/types, types2: tweak missingMethodReason logic to improve message

This makes the error case pointed out in the issue like the current
message in Go 1.17 or -G=0 mode. The priority is to point out the
similar but wrong method name, rather than a difference in type.

Made changes to both cmd/compile/internal/types2 and go/types.
Added in a missing tab in an error message in go/types.

At the same time, removed the extra "at info" on the have lines (and
pointer receiver lines) of error messages, as requested in #50907.

Fixes #50816
Fixes #50907

Change-Id: I04f8151955bdb6192246cbcb59adc1c4b8a2c4e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/381774
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

@@ -403,20 +403,18 @@ func (check *Checker) missingMethodReason(V, T Type, m, wrongType *Func) string
 		mname = "method " + m.Name()
 	}
 	if wrongType != nil {
-		if Identical(m.typ, wrongType.typ) {
-			if m.Name() == wrongType.Name() {
-				r = check.sprintf("(%s has pointer receiver) at %s", mname, wrongType.Pos())
-			} else {
-				r = check.sprintf("(missing %s)\n\t\thave %s^^%s at %s\n\t\twant %s^^%s",
-					mname, wrongType.Name(), wrongType.typ, wrongType.Pos(), m.Name(), m.typ)
-			}
+		if m.Name() != wrongType.Name() {
+			r = check.sprintf("(missing %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
+				mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
+		} else if Identical(m.typ, wrongType.typ) {
+			r = check.sprintf("(%s has pointer receiver)", mname)
 		} else {
 			if check.conf.CompilerErrorMessages {
-				r = check.sprintf("(wrong type for %s)\n\t\thave %s^^%s at %s\n\t\twant %s^^%s",
-					mname, wrongType.Name(), wrongType.typ, wrongType.Pos(), m.Name(), m.typ)
+				r = check.sprintf("(wrong type for %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
+					mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
 			} else {
-				r = check.sprintf("(wrong type for %s)\n\thave %s at %s\n\twant %s",
-					mname, wrongType.typ, wrongType.Pos(), m.typ)
+				r = check.sprintf("(wrong type for %s)\n\thave %s\n\twant %s",
+					mname, wrongType.typ, m.typ)
 			}
 		}
 		// This is a hack to print the function type without the leading

src/cmd/compile/internal/types2/testdata/check/issues.src

@@ -137,7 +137,7 @@ func issue10260() {
 	T1{}.foo /* ERROR cannot call pointer method foo on T1 */ ()
 	x.Foo /* ERROR "x.Foo undefined \(type I1 has no field or method Foo, but does have foo\)" */ ()
 
-	_ = i2. /* ERROR impossible type assertion: i2.\(\*T1\)\n\t\*T1 does not implement I2 \(wrong type for method foo\)\n\thave func\(\) at \w+.+\d+.\d+\n\twant func\(x int\) */ (*T1)
+	_ = i2. /* ERROR impossible type assertion: i2.\(\*T1\)\n\t\*T1 does not implement I2 \(wrong type for method foo\)\n\thave func\(\)\n\twant func\(x int\) */ (*T1)
 
 	i1 = i0 /* ERROR cannot use .* missing method foo */
 	i1 = t0 /* ERROR cannot use .* missing method foo */

src/cmd/compile/internal/types2/testdata/fixedbugs/issue50816.go2

@@ -0,0 +1,23 @@
+// 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 pkg
+
+type I interface {
+	Foo()
+}
+
+type T1 struct{}
+
+func (T1) foo() {}
+
+type T2 struct{}
+
+func (T2) foo() string { return "" }
+
+func _() {
+	var i I
+	_ = i./* ERROR impossible type assertion: i.\(T1\)\n\tT1 does not implement I \(missing method Foo\)\n\t\thave foo\(\)\n\t\twant Foo\(\) */ (T1)
+	_ = i./* ERROR impossible type assertion: i.\(T2\)\n\tT2 does not implement I \(missing method Foo\)\n\t\thave foo\(\) string\n\t\twant Foo\(\) */ (T2)
+}

src/go/types/lookup.go

@@ -390,21 +390,20 @@ func (check *Checker) missingMethodReason(V, T Type, m, wrongType *Func) string
 		mname = "method " + m.Name()
 	}
 	if wrongType != nil {
-		pos := check.fset.Position(wrongType.Pos())
-		if Identical(m.typ, wrongType.typ) {
-			if m.Name() == wrongType.Name() {
-				r = check.sprintf("(%s has pointer receiver) at %s", mname, pos)
-			} else {
-				r = check.sprintf("(missing %s)\n\t\thave %s^^%s at %s\n\t\twant %s^^%s",
-					mname, wrongType.Name(), wrongType.typ, pos, m.Name(), m.typ)
-			}
+		if m.Name() != wrongType.Name() {
+			// Note: this case can't happen because we don't look for alternative
+			// method spellings, unlike types2. Keep for symmetry with types2.
+			r = check.sprintf("(missing %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
+				mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
+		} else if Identical(m.typ, wrongType.typ) {
+			r = check.sprintf("(%s has pointer receiver)", mname)
 		} else {
 			if compilerErrorMessages {
-				r = check.sprintf("(wrong type for %s)\n\t\thave %s^^%s at %s\n\t\twant %s^^%s",
-					mname, wrongType.Name(), wrongType.typ, pos, m.Name(), m.typ)
+				r = check.sprintf("(wrong type for %s)\n\t\thave %s^^%s\n\t\twant %s^^%s",
+					mname, wrongType.Name(), wrongType.typ, m.Name(), m.typ)
 			} else {
-				r = check.sprintf("(wrong type for %s)\n\thave %s at %s\nwant %s",
-					mname, wrongType.typ, pos, m.typ)
+				r = check.sprintf("(wrong type for %s)\n\thave %s\n\twant %s",
+					mname, wrongType.typ, m.typ)
 			}
 		}
 		// This is a hack to print the function type without the leading

src/go/types/testdata/fixedbugs/issue50816.go2

@@ -0,0 +1,23 @@
+// 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 pkg
+
+type I interface {
+	Foo()
+}
+
+type T1 struct{}
+
+func (T1) foo() {}
+
+type T2 struct{}
+
+func (T2) foo() string { return "" }
+
+func _() {
+	var i I
+	_ = i/* ERROR i \(variable of type I\) cannot have dynamic type T1 \(missing method Foo\) */.(T1)
+	_ = i/* ERROR i \(variable of type I\) cannot have dynamic type T2 \(missing method Foo\) */.(T2)
+}

test/fixedbugs/issue48471.go

@@ -22,19 +22,34 @@ type T4 struct{}
 
 func (*T4) M(int)
 
+type T5 struct{}
+
+func (T5) m(int) {}
+
+type T6 struct{}
+
+func (T6) m(int) string { return "" }
+
 func f(I)
 
 func g() {
 	f(new(T)) // ERROR "cannot use new\(T\) \(.*type \*T\) as type I in argument to f:\n\t\*T does not implement I \(missing M method\)"
+
 	var i I
 	i = new(T)    // ERROR "cannot use new\(T\) \(.*type \*T\) as type I in assignment:\n\t\*T does not implement I \(missing M method\)"
 	i = I(new(T)) // ERROR "cannot convert new\(T\) \(.*type \*T\) to type I:\n\t\*T does not implement I \(missing M method\)"
-	i = new(T2)   // ERROR "cannot use new\(T2\) \(.*type \*T2\) as type I in assignment:\n\t\*T2 does not implement I \(missing M method\)\n\t\thave m\(int\) at \w+.+\d.\d+\n\t\twant M\(int\)"
-	i = new(T3)   // ERROR "cannot use new\(T3\) \(.*type \*T3\) as type I in assignment:\n\t\*T3 does not implement I \(wrong type for M method\)\n\t\thave M\(string\) at \w+.+\d.\d+\n\t\twant M\(int\)"
-	i = T4{}      // ERROR "cannot use T4\{\} \(.*type T4\) as type I in assignment:\n\tT4 does not implement I \(M method has pointer receiver\)"
-	i = new(I)    // ERROR "cannot use new\(I\) \(.*type \*I\) as type I in assignment:\n\t\*I does not implement I \(type \*I is pointer to interface, not interface\)"
-	_ = i.(*T2)   // ERROR "impossible type assertion: i.\(\*T2\)\n\t\*T2 does not implement I \(missing M method\)\n\t\thave m\(int\) at \w+.+\d.\d+\n\t\twant M\(int\)"
-	_ = i.(*T3)   // ERROR "impossible type assertion: i.\(\*T3\)\n\t\*T3 does not implement I \(wrong type for M method\)\n\t\thave M\(string\) at \w+.+\d.\d+\n\t\twant M\(int\)"
+	i = new(T2)   // ERROR "cannot use new\(T2\) \(.*type \*T2\) as type I in assignment:\n\t\*T2 does not implement I \(missing M method\)\n\t\thave m\(int\)\n\t\twant M\(int\)"
+
+	i = new(T3) // ERROR "cannot use new\(T3\) \(.*type \*T3\) as type I in assignment:\n\t\*T3 does not implement I \(wrong type for M method\)\n\t\thave M\(string\)\n\t\twant M\(int\)"
+
+	i = T4{}   // ERROR "cannot use T4\{\} \(.*type T4\) as type I in assignment:\n\tT4 does not implement I \(M method has pointer receiver\)"
+	i = new(I) // ERROR "cannot use new\(I\) \(.*type \*I\) as type I in assignment:\n\t\*I does not implement I \(type \*I is pointer to interface, not interface\)"
+
+	_ = i.(*T2) // ERROR "impossible type assertion: i.\(\*T2\)\n\t\*T2 does not implement I \(missing M method\)\n\t\thave m\(int\)\n\t\twant M\(int\)"
+	_ = i.(*T3) // ERROR "impossible type assertion: i.\(\*T3\)\n\t\*T3 does not implement I \(wrong type for M method\)\n\t\thave M\(string\)\n\t\twant M\(int\)"
+	_ = i.(T5)  // ERROR ""impossible type assertion: i.\(T5\)\n\tT5 does not implement I \(missing M method\)\n\t\thave m\(int\)\n\t\twant M\(int\)"
+	_ = i.(T6)  // ERROR "impossible type assertion: i.\(T6\)\n\tT6 does not implement I \(missing M method\)\n\t\thave m\(int\) string\n\t\twant M\(int\)"
+
 	var t *T4
 	t = i // ERROR "cannot use i \(variable of type I\) as type \*T4 in assignment:\n\tneed type assertion"
 	_ = i