Simplify implementation and document edge cases

Simplify implementation to not worry about spaces consistency. Instead, just
preserve spaces before comments as-is.

Also add examples that show when comments still aren't handled consistently.

Author: willbeason

goldens/trailing_commas.in

@@ -16,18 +16,26 @@ Trailing comma and a comment
 Trailing comma except for last, last has a comment
   keep-sorted-test start
   3,
-  1,
-  2  # two
+  1, <!-- one -->
+  2  <!-- two -->
   keep-sorted-test end
 
 Trailing comma and a comment, last has a comment
   keep-sorted-test start
-  3, # three
+  3, -- three
   1,
-  2  # two
+  2  -- two
+  keep-sorted-test end
+
+Trailing commas with inline comment
+  keep-sorted-test start
+  "c" /* c */,
+  "b",
+  "a" /* a */
   keep-sorted-test end
 
 Trailing commas with quoted comment characters
+TODO: https://github.com/google/keep-sorted/issues/33 - Fix this
   keep-sorted-test start
   "c",
   "b, //",

goldens/trailing_commas.out

@@ -10,24 +10,32 @@ Trailing comma and a comment
   keep-sorted-test start
   1,
   2,
-  3  # three
+  3 # three
   keep-sorted-test end
 
 Trailing comma except for last, last has a comment
   keep-sorted-test start
-  1,
-  2, # two
+  1, <!-- one -->
+  2,  <!-- two -->
   3
   keep-sorted-test end
 
 Trailing comma and a comment, last has a comment
   keep-sorted-test start
   1,
-  2, # two
-  3  # three
+  2,  -- two
+  3 -- three
+  keep-sorted-test end
+
+Trailing commas with inline comment
+  keep-sorted-test start
+  "a", /* a */
+  "b",
+  "c" /* c */
   keep-sorted-test end
 
 Trailing commas with quoted comment characters
+TODO: https://github.com/google/keep-sorted/issues/33 - Fix this
   keep-sorted-test start
   "a, #"
   "b, //",

keepsorted/block.go

@@ -15,6 +15,7 @@
 package keepsorted
 
 import (
+	"fmt"
 	"regexp"
 	"slices"
 	"strings"
@@ -385,24 +386,23 @@ func handleTrailingComma(lgs []*lineGroup) (trimTrailingComma func([]*lineGroup)
 		}
 	}
 
-	commaLineEnd := regexp.MustCompile("(,)( *)((#|//).*)?$")
-	commentLineEnd := regexp.MustCompile("( *)((#|//).*)$")
+	knownCommentMarkersList := knownCommentMarkers()
+	for i, marker := range knownCommentMarkersList {
+		// Some comment markers, such as "/*", include regex metacharacters.
+		knownCommentMarkersList[i] = regexp.QuoteMeta(marker)
+	}
+	knownCommentMarkersStr := strings.Join(knownCommentMarkersList, "|")
+
+	commaLineEnd := regexp.MustCompile(fmt.Sprintf(",(\\s*(%s).*)?$", knownCommentMarkersStr))
+	lineEnd := regexp.MustCompile(fmt.Sprintf("(\\s*(%s).*)?$", knownCommentMarkersStr))
 
 	if n := len(dataGroups); n > 1 && allMatchSuffix(dataGroups[0:n-1], commaLineEnd) && !dataGroups[n-1].matchesSuffix(commaLineEnd) {
-		if dataGroups[n-1].matchesSuffix(commentLineEnd) {
-			dataGroups[n-1].replaceSuffix(commentLineEnd, ", $2")
-		} else {
-			dataGroups[n-1].append(",")
-		}
+		dataGroups[n-1].replaceSuffix(lineEnd, ",$1")
 
 		return func(lgs []*lineGroup) {
 			for i := len(lgs) - 1; i >= 0; i-- {
 				if len(lgs[i].lines) > 0 {
-					if lgs[i].matchesSuffix(commentLineEnd) {
-						lgs[i].replaceSuffix(commaLineEnd, "  $3")
-					} else {
-						lgs[i].trimSuffix(",")
-					}
+					lgs[i].replaceSuffix(commaLineEnd, "$1")
 					return
 				}
 			}

keepsorted/keep_sorted_test.go

@@ -1126,6 +1126,21 @@ func TestLineSorting(t *testing.T) {
 				"foo",
 			},
 		},
+		{
+			name: "TrailingCommas_WithComments",
+
+			in: []string{
+				"foo,",
+				"baz, /* baz */",
+				"bar // bar",
+			},
+
+			want: []string{
+				"bar, // bar",
+				"baz, /* baz */",
+				"foo",
+			},
+		},
 		{
 			name: "IgnorePrefixes",
 

keepsorted/options.go

@@ -312,9 +312,13 @@ func formatIntList(intVals []int) string {
 	return strings.Join(vals, ",")
 }
 
+func knownCommentMarkers() []string {
+	return []string{"//", "#", "/*", "--", ";", "<!--"}
+}
+
 func guessCommentMarker(startLine string) string {
 	startLine = strings.TrimSpace(startLine)
-	for _, marker := range []string{"//", "#", "/*", "--", ";", "<!--"} {
+	for _, marker := range knownCommentMarkers() {
 		if strings.HasPrefix(startLine, marker) {
 			return marker
 		}