go/scanner: Stabilize (*ErrorList).Sort

This change stabilizes the result of Sort when the error list contains
multiple items for same position. To stabilize the result, newly also
the Msg field is considered.

The motivation is to avoid diffs of sorted scanner.ErrorList output
in repository tracked logs like:

-testdata/foo.go:19:44: "bar"
 testdata/foo.go:19:44: "qux"
+testdata/foo.go:19:44: "bar"

The change was approved at [0] before submitting.

As a side effect, one file in go/parser/testdata must be updated as
well. For this file the parser produces two different errors:

testdata/issue3106.src:22:5: expected ';', found 'if'
testdata/issue3106.src:22:5: expected operand, found 'if'

Before comparing the actual and expected errors, the former are
filtered to keep only one error per source line[1]. With the new
(*ErrorList).Less the outcome is the other error than before which is
kept after the call to RemoveMultiplies.

[0]: https://groups.google.com/d/msg/golang-nuts/5ChC0XiIwlU/rol_yb2gTj4J
[1]:
https://github.com/golang/go/blob/9d0239771a2ddd77be0ba64c2782e1328a378190/src/go/parser/error_test.go#L160

Change-Id: Ib72c98a891cdeef34705c22dfbeb0408dcdfddf8
Reviewed-on: https://go-review.googlesource.com/8340
Reviewed-by: Robert Griesemer <gri@golang.org>

diff --git a/src/go/parser/testdata/issue3106.src b/src/go/parser/testdata/issue3106.src
index 82796c8ceb650e0dbad83f43eabdb5ed9c3d3737..2db10be23549b96b55c4d5a14c71fe484cb59a45 100644 (file)
--- a/src/go/parser/testdata/issue3106.src
+++ b/src/go/parser/testdata/issue3106.src
@@ -19,7 +19,7 @@ func f() {
                                time.Sleep(1e8)
                                m.Lock()
                                defer
-                               if /* ERROR "expected operand, found 'if'" */ percent == 100 {
+                               if /* ERROR "expected ';', found 'if'" */ percent == 100 {
                                        m.Unlock()
                                        break
                                }

diff --git a/src/go/scanner/errors.go b/src/go/scanner/errors.go
index 22de69c3c1c824a7d773b4fdfe700fa43172da08..7c9ab254eed26ea8a23341b65dd5100a3fb4e8d4 100644 (file)
--- a/src/go/scanner/errors.go
+++ b/src/go/scanner/errors.go
@@ -62,7 +62,14 @@ func (p ErrorList) Less(i, j int) bool {
                        return true
                }
                if e.Line == f.Line {
-                       return e.Column < f.Column
+                       if e.Column < f.Column {
+                               return true
+                       }
+                       if e.Column == f.Column {
+                               if p[i].Msg < p[j].Msg {
+                                       return true
+                               }
+                       }
                }
        }
        return false