go/types: better position for invalid slice indices error

This is a port of CL 363671 from types2 to go/types. Also adjust the
error message to match types2 ("invalid" vs "swapped").

Change-Id: I662a73c915814fea14bfcb1ebde0fbf39589f022
Reviewed-on: https://go-review.googlesource.com/c/go/+/364902
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

diff --git a/src/go/types/index.go b/src/go/types/index.go
index 6ea25bc764f6d0d9a6fcb4ad24156eb68650f0e3..db4732c8e00e466ee5e6e53f646802a952d2b1aa 100644 (file)
--- a/src/go/types/index.go
+++ b/src/go/types/index.go
@@ -310,9 +310,13 @@ func (check *Checker) sliceExpr(x *operand, e *ast.SliceExpr) {
 L:
        for i, x := range ind[:len(ind)-1] {
                if x > 0 {
-                       for _, y := range ind[i+1:] {
-                               if y >= 0 && x > y {
-                                       check.errorf(inNode(e, e.Rbrack), _SwappedSliceIndices, "swapped slice indices: %d > %d", x, y)
+                       for j, y := range ind[i+1:] {
+                               if y >= 0 && y < x {
+                                       // The value y corresponds to the expression e.Index[i+1+j].
+                                       // Because y >= 0, it must have been set from the expression
+                                       // when checking indices and thus e.Index[i+1+j] is not nil.
+                                       at := []ast.Expr{e.Low, e.High, e.Max}[i+1+j]
+                                       check.errorf(at, _SwappedSliceIndices, "invalid slice indices: %d < %d", y, x)
                                        break L // only report one error, ok to continue
                                }
                        }

diff --git a/src/go/types/testdata/check/expr3.src b/src/go/types/testdata/check/expr3.src
index a63542b843dff88909ff033206cc96e462143602..5117a0373b8cc8392ebe86df28aca1c7d73124dc 100644 (file)
--- a/src/go/types/testdata/check/expr3.src
+++ b/src/go/types/testdata/check/expr3.src
@@ -44,9 +44,9 @@ func indexes() {
        _ = a[:10:10]
        _ = a[:11 /* ERROR "index .* out of bounds" */ :10]
        _ = a[:10:11 /* ERROR "index .* out of bounds" */ ]
-       _ = a[10:0:10] /* ERROR swapped slice indices" */
-       _ = a[0:10:0] /* ERROR "swapped slice indices" */
-       _ = a[10:0:0] /* ERROR "swapped slice indices" */
+       _ = a[10:0 /* ERROR "invalid slice indices" */ :10]
+       _ = a[0:10:0 /* ERROR "invalid slice indices" */ ]
+       _ = a[10:0 /* ERROR "invalid slice indices" */:0]
        _ = &a /* ERROR "cannot take address" */ [:10]
 
        pa := &a
@@ -62,9 +62,9 @@ func indexes() {
        _ = pa[:10:10]
        _ = pa[:11 /* ERROR "index .* out of bounds" */ :10]
        _ = pa[:10:11 /* ERROR "index .* out of bounds" */ ]
-       _ = pa[10:0:10] /* ERROR "swapped slice indices" */
-       _ = pa[0:10:0] /* ERROR "swapped slice indices" */
-       _ = pa[10:0:0] /* ERROR "swapped slice indices" */
+       _ = pa[10:0 /* ERROR "invalid slice indices" */ :10]
+       _ = pa[0:10:0 /* ERROR "invalid slice indices" */ ]
+       _ = pa[10:0 /* ERROR "invalid slice indices" */ :0]
        _ = &pa /* ERROR "cannot take address" */ [:10]
 
        var b [0]int
@@ -82,16 +82,16 @@ func indexes() {
        _ = s[: - /* ERROR "negative" */ 1]
        _ = s[0]
        _ = s[1:2]
-       _ = s[2:1] /* ERROR "swapped slice indices" */
+       _ = s[2:1 /* ERROR "invalid slice indices" */ ]
        _ = s[2:]
        _ = s[: 1 /* ERROR "overflows" */ <<100]
        _ = s[1 /* ERROR "overflows" */ <<100 :]
        _ = s[1 /* ERROR "overflows" */ <<100 : 1 /* ERROR "overflows" */ <<100]
        _ = s[: /* ERROR "2nd index required" */ :  /* ERROR "3rd index required" */ ]
        _ = s[:10:10]
-       _ = s[10:0:10] /* ERROR "swapped slice indices" */
-       _ = s[0:10:0] /* ERROR "swapped slice indices" */
-       _ = s[10:0:0] /* ERROR "swapped slice indices" */
+       _ = s[10:0 /* ERROR "invalid slice indices" */ :10]
+       _ = s[0:10:0 /* ERROR "invalid slice indices" */ ]
+       _ = s[10:0 /* ERROR "invalid slice indices" */ :0]
        _ = &s /* ERROR "cannot take address" */ [:10]
 
        var m map[string]int