go/types, types2: avoid sorting all errors when matching errors

Sorting is only needed if there are multiple matching errors on
the same line. Instead, in that rare case, select the error that
is closest.

Follow-up on CL 456137.

Change-Id: Ia2056b21c629f3a42495e32de89607fbefb82fa7
Reviewed-on: https://go-review.googlesource.com/c/go/+/456335
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>

1 files changed, 20 insertions, 19 deletions

diff --git a/src/cmd/compile/internal/types2/check_test.go b/src/cmd/compile/internal/types2/check_test.go
index 0f97fe9680..611466ba01 100644
--- a/src/cmd/compile/internal/types2/check_test.go
+++ b/src/cmd/compile/internal/types2/check_test.go
@@ -31,7 +31,6 @@ import (
 	"os"
 	"path/filepath"
 	"regexp"
-	"sort"
 	"strings"
 	"testing"
 
@@ -68,8 +67,8 @@ func unpackError(err error) (syntax.Pos, string) {
 	}
 }
 
-// delta returns the absolute difference between x and y.
-func delta(x, y uint) uint {
+// absDiff returns the absolute difference between x and y.
+func absDiff(x, y uint) uint {
 	if x < y {
 		return y - x
 	}
@@ -165,13 +164,6 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 		return
 	}
 
-	// sort errlist in source order
-	sort.Slice(errlist, func(i, j int) bool {
-		pi, _ := unpackError(errlist[i])
-		pj, _ := unpackError(errlist[j])
-		return pi.Cmp(pj) < 0
-	})
-
 	// collect expected errors
 	errmap := make(map[string]map[uint][]syntax.Error)
 	for _, filename := range filenames {
@@ -187,6 +179,7 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 	}
 
 	// match against found errors
+	var indices []int // list indices of matching errors, reused for each error
 	for _, err := range errlist {
 		gotPos, gotMsg := unpackError(err)
 
@@ -199,8 +192,8 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 			errList = filemap[line]
 		}
 
-		// one of errors in errList should match the current error
-		index := -1 // errList index of matching message, if any
+		// At least one of the errors in errList should match the current error.
+		indices = indices[:0]
 		for i, want := range errList {
 			pattern := strings.TrimSpace(want.Msg[len(" ERROR "):])
 			if n := len(pattern); n >= 2 && pattern[0] == '"' && pattern[n-1] == '"' {
@@ -212,19 +205,27 @@ func testFiles(t *testing.T, filenames []string, colDelta uint, manual bool) {
 				continue
 			}
 			if rx.MatchString(gotMsg) {
-				index = i
-				break
+				indices = append(indices, i)
 			}
 		}
-		if index < 0 {
+		if len(indices) == 0 {
 			t.Errorf("%s: no error expected: %q", gotPos, gotMsg)
 			continue
 		}
+		// len(indices) > 0
+
+		// If there are multiple matching errors, select the one with the closest column position.
+		index := -1 // index of matching error
+		var delta uint
+		for _, i := range indices {
+			if d := absDiff(gotPos.Col(), errList[i].Pos.Col()); index < 0 || d < delta {
+				index, delta = i, d
+			}
+		}
 
-		// column position must be within expected colDelta
-		want := errList[index]
-		if delta(gotPos.Col(), want.Pos.Col()) > colDelta {
-			t.Errorf("%s: got col = %d; want %d", gotPos, gotPos.Col(), want.Pos.Col())
+		// The closest column position must be within expected colDelta.
+		if delta > colDelta {
+			t.Errorf("%s: got col = %d; want %d", gotPos, gotPos.Col(), errList[index].Pos.Col())
 		}
 
 		// eliminate from errList