go/types, types2: use 2nd operand position for comparison type mismatch errors

When a comparison is invalid due to mismatched types, we only know
when we see the 2nd operand; so use that operand's position for the
error message. This matches compiler behavior.

For #55326.

Change-Id: I79450756bbdd2b4bb90ed4e960a451be0197b186
Reviewed-on: https://go-review.googlesource.com/c/go/+/435555
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

5 files changed, 30 insertions, 40 deletions

diff --git a/src/cmd/compile/internal/types2/expr.go b/src/cmd/compile/internal/types2/expr.go
index c700667034..1f27871c42 100644
--- a/src/cmd/compile/internal/types2/expr.go
+++ b/src/cmd/compile/internal/types2/expr.go
@@ -788,11 +788,6 @@ func (check *Checker) comparison(x, y *operand, op syntax.Operator, switchCase b
 		// know after seeing the 2nd operand whether we have
 		// a type mismatch.
 		errOp = y
-		// For now, if we're not running the compiler, use the
-		// position of x to minimize changes to existing tests.
-		if !check.conf.CompilerErrorMessages {
-			errOp = x
-		}
 		cause = check.sprintf("mismatched types %s and %s", x.typ, y.typ)
 		goto Error
 	}
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index ebb107b8c0..06a0de7c35 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -765,11 +765,6 @@ func (check *Checker) comparison(x, y *operand, op token.Token, switchCase bool)
 		// know after seeing the 2nd operand whether we have
 		// a type mismatch.
 		errOp = y
-		// For now, if we're not running the compiler, use the
-		// position of x to minimize changes to existing tests.
-		if !compilerErrorMessages {
-			errOp = x
-		}
 		cause = check.sprintf("mismatched types %s and %s", x.typ, y.typ)
 		goto Error
 	}
diff --git a/src/internal/types/testdata/check/const0.go b/src/internal/types/testdata/check/const0.go
index 229c248643..402e6cf5a9 100644
--- a/src/internal/types/testdata/check/const0.go
+++ b/src/internal/types/testdata/check/const0.go
@@ -27,7 +27,7 @@ const (
 	ub1 = true
 	ub2 = 2 < 1
 	ub3 = ui1 == uf1
-	ub4 = true /* ERROR "mismatched types untyped bool and untyped int" */ == 0
+	ub4 = true == 0 /* ERROR "mismatched types untyped bool and untyped int" */
 
 	// integer values
 	ui0 = 0
@@ -110,7 +110,7 @@ const (
 	tb0 bool = false
 	tb1 bool = true
 	tb2 mybool = 2 < 1
-	tb3 mybool = ti1 /* ERROR "mismatched types" */ == tf1
+	tb3 mybool = ti1 == tf1 /* ERROR "mismatched types" */
 
 	// integer values
 	ti0 int8 = ui0
diff --git a/src/internal/types/testdata/check/expr2.go b/src/internal/types/testdata/check/expr2.go
index 6133dbb42b..1cb65ad2a2 100644
--- a/src/internal/types/testdata/check/expr2.go
+++ b/src/internal/types/testdata/check/expr2.go
@@ -10,7 +10,7 @@ func _bool() {
 	const t = true == true
 	const f = true == false
 	_ = t /* ERROR cannot compare */ < f
-	_ = 0 /* ERROR mismatched types untyped int and untyped bool */ == t
+	_ = 0 == t /* ERROR mismatched types untyped int and untyped bool */
 	var b bool
 	var x, y float32
 	b = x < y
@@ -29,7 +29,7 @@ func arrays() {
 	_ = a == b
 	_ = a != b
 	_ = a /* ERROR < not defined */ < b
-	_ = a /* ERROR cannot compare.*mismatched types */ == nil
+	_ = a == nil /* ERROR cannot compare.*mismatched types */
 
 	type C [10]int
 	var c C
@@ -37,7 +37,7 @@ func arrays() {
 
 	type D [10]int
 	var d D
-	_ = c /* ERROR mismatched types */ == d
+	_ = c == d /* ERROR mismatched types */
 
 	var e [10]func() int
 	_ = e /* ERROR \[10\]func\(\) int cannot be compared */ == e
@@ -53,7 +53,7 @@ func structs() {
 	_ = s == t
 	_ = s != t
 	_ = s /* ERROR < not defined */ < t
-	_ = s /* ERROR cannot compare.*mismatched types */ == nil
+	_ = s == nil /* ERROR cannot compare.*mismatched types */
 
 	type S struct {
 		x int
@@ -68,7 +68,7 @@ func structs() {
 	var ss S
 	var tt T
 	_ = s == ss
-	_ = ss /* ERROR mismatched types */ == tt
+	_ = ss == tt /* ERROR mismatched types */
 
 	var u struct {
 		x int
@@ -115,11 +115,11 @@ func pointers() {
 		p2 P2
 	)
 	_ = ps1 == ps1
-	_ = ps1 /* ERROR mismatched types */ == ps2
-	_ = ps2 /* ERROR mismatched types */ == ps1
+	_ = ps1 == ps2 /* ERROR mismatched types */
+	_ = ps2 == ps1 /* ERROR mismatched types */
 
 	_ = p1 == p1
-	_ = p1 /* ERROR mismatched types */ == p2
+	_ = p1 == p2 /* ERROR mismatched types */
 
 	_ = p1 == ps1
 }
@@ -147,13 +147,13 @@ func channels() {
 		c2 C2
 	)
 	_ = c1 == c1
-	_ = c1 /* ERROR mismatched types */ == c1r
-	_ = c1 /* ERROR mismatched types */ == c1s
-	_ = c1r /* ERROR mismatched types */ == c1s
+	_ = c1 == c1r /* ERROR mismatched types */
+	_ = c1 == c1s /* ERROR mismatched types */
+	_ = c1r == c1s /* ERROR mismatched types */
 	_ = c1 == c1a
 	_ = c1a == c1
-	_ = c1 /* ERROR mismatched types */ == c2
-	_ = c1a /* ERROR mismatched types */ == c2
+	_ = c1 == c2 /* ERROR mismatched types */
+	_ = c1a == c2 /* ERROR mismatched types */
 
 	// various element types (unnamed types)
 	var (
@@ -166,11 +166,11 @@ func channels() {
 	_ = d1 == d1
 	_ = d1 == d1r
 	_ = d1 == d1s
-	_ = d1r /* ERROR mismatched types */ == d1s
+	_ = d1r == d1s /* ERROR mismatched types */
 	_ = d1 == d1a
 	_ = d1a == d1
-	_ = d1 /* ERROR mismatched types */ == d2
-	_ = d1a /* ERROR mismatched types */ == d2
+	_ = d1 == d2 /* ERROR mismatched types */
+	_ = d1a == d2 /* ERROR mismatched types */
 }
 
 // for interfaces test
@@ -194,7 +194,7 @@ func interfaces() {
 	var ii interface { m() int; n() }
 	var k interface { m() float32 }
 	_ = i == ii
-	_ = i /* ERROR mismatched types */ == k
+	_ = i == k /* ERROR mismatched types */
 
 	// interfaces vs values
 	var s1 S1
@@ -202,12 +202,12 @@ func interfaces() {
 	var s2 S2
 
 	_ = i == 0 /* ERROR cannot convert */
-	_ = i /* ERROR mismatched types */ == s1
+	_ = i == s1 /* ERROR mismatched types */
 	_ = i == &s1
 	_ = i == &s11
 
-	_ = i /* ERROR mismatched types */ == s2
-	_ = i /* ERROR mismatched types */ == &s2
+	_ = i == s2 /* ERROR mismatched types */
+	_ = i == & /* ERROR mismatched types */ s2
 
 	// issue #28164
 	// testcase from issue
diff --git a/src/internal/types/testdata/spec/comparisons.go b/src/internal/types/testdata/spec/comparisons.go
index 2a7598a581..886e78c0a7 100644
--- a/src/internal/types/testdata/spec/comparisons.go
+++ b/src/internal/types/testdata/spec/comparisons.go
@@ -40,10 +40,10 @@ func _() {
 	_ = m /* ERROR map can only be compared to nil */ == m
 	_ = c == c
 
-	_ = b /* ERROR mismatched types */ == nil
-	_ = a /* ERROR mismatched types */ == nil
+	_ = b == nil /* ERROR mismatched types */
+	_ = a == nil /* ERROR mismatched types */
 	_ = l == nil
-	_ = s /* ERROR mismatched types */ == nil
+	_ = s == nil /* ERROR mismatched types */
 	_ = p == nil
 	_ = f == nil
 	_ = i == nil
@@ -96,14 +96,14 @@ func _[
 	_ = m /* ERROR incomparable types in type set */ == m
 	_ = c == c
 
-	_ = b /* ERROR mismatched types */ == nil
-	_ = a /* ERROR mismatched types */ == nil
+	_ = b == nil /* ERROR mismatched types */
+	_ = a == nil /* ERROR mismatched types */
 	_ = l == nil
-	_ = s /* ERROR mismatched types */ == nil
+	_ = s == nil /* ERROR mismatched types */
 	_ = p == nil
 	_ = f == nil
-	_ = i /* ERROR mismatched types */ == nil
-	_ = j /* ERROR mismatched types */ == nil
+	_ = i == nil /* ERROR mismatched types */
+	_ = j == nil /* ERROR mismatched types */
 	_ = m == nil
 	_ = c == nil