Crucible: Fix Formatting Churn

internal/topdata/editorconfig_format.go

@@ -203,8 +203,23 @@ func editorConfigPatternMatches(pattern, relativePath string) (bool, error) {
 }
 
 func editorConfigGlobRegexp(pattern string) (string, error) {
+	body, err := translateEditorConfigGlobSegment(pattern)
+	if err != nil {
+		return "", err
+	}
+	expression := "^" + body + "$"
+	if _, err := regexp.Compile(expression); err != nil {
+		return "", err
+	}
+	return expression, nil
+}
+
+// translateEditorConfigGlobSegment converts an editorconfig glob into a regular
+// expression body. In addition to *, **, and ?, it implements brace expansion:
+// comma lists ({a,b,c}) become alternations and numeric ranges ({n..m}) expand
+// to the integers in the range, matching the editorconfig specification.
+func translateEditorConfigGlobSegment(pattern string) (string, error) {
 	var builder strings.Builder
-	builder.WriteByte('^')
 	for index := 0; index < len(pattern); {
 		char := pattern[index]
 		switch char {
@@ -220,22 +235,132 @@ func editorConfigGlobRegexp(pattern string) (string, error) {
 				continue
 			}
 			builder.WriteString("[^/]*")
+			index++
 		case '?':
 			builder.WriteString("[^/]")
-		case '.', '+', '(', ')', '|', '^', '$', '{', '}', '[', ']', '\\':
+			index++
+		case '{':
+			end := matchingEditorConfigBrace(pattern, index)
+			if end < 0 {
+				// An unbalanced brace is matched literally.
+				builder.WriteString("\\{")
+				index++
+				continue
+			}
+			expansion, err := expandEditorConfigBrace(pattern[index+1 : end])
+			if err != nil {
+				return "", err
+			}
+			builder.WriteString(expansion)
+			index = end + 1
+		case '.', '+', '(', ')', '|', '^', '$', '}', '[', ']', '\\':
 			builder.WriteByte('\\')
 			builder.WriteByte(char)
+			index++
 		default:
 			builder.WriteByte(char)
+			index++
 		}
-		index++
 	}
-	builder.WriteByte('$')
-	expression := builder.String()
-	if _, err := regexp.Compile(expression); err != nil {
-		return "", err
+	return builder.String(), nil
+}
+
+// matchingEditorConfigBrace returns the index of the '}' that closes the '{' at
+// open, accounting for nesting, or -1 when the braces are unbalanced.
+func matchingEditorConfigBrace(pattern string, open int) int {
+	depth := 0
+	for index := open; index < len(pattern); index++ {
+		switch pattern[index] {
+		case '{':
+			depth++
+		case '}':
+			depth--
+			if depth == 0 {
+				return index
+			}
+		}
 	}
-	return expression, nil
+	return -1
+}
+
+// expandEditorConfigBrace turns the body of a brace expression into a regex
+// fragment. A comma list becomes an alternation; a lone "n..m" body becomes a
+// numeric range. A body with neither comma nor range is treated as literal
+// braces, matching the editorconfig reference implementation.
+func expandEditorConfigBrace(inner string) (string, error) {
+	options := splitTopLevelBraceCommas(inner)
+	if len(options) == 1 {
+		if rangeExpr, ok, err := editorConfigNumericRange(inner); err != nil {
+			return "", err
+		} else if ok {
+			return rangeExpr, nil
+		}
+		segment, err := translateEditorConfigGlobSegment(inner)
+		if err != nil {
+			return "", err
+		}
+		return "\\{" + segment + "\\}", nil
+	}
+	parts := make([]string, 0, len(options))
+	for _, option := range options {
+		segment, err := translateEditorConfigGlobSegment(option)
+		if err != nil {
+			return "", err
+		}
+		parts = append(parts, segment)
+	}
+	return "(?:" + strings.Join(parts, "|") + ")", nil
+}
+
+// splitTopLevelBraceCommas splits a brace body on commas that are not nested
+// inside an inner brace group.
+func splitTopLevelBraceCommas(inner string) []string {
+	parts := []string{}
+	depth := 0
+	start := 0
+	for index := 0; index < len(inner); index++ {
+		switch inner[index] {
+		case '{':
+			depth++
+		case '}':
+			depth--
+		case ',':
+			if depth == 0 {
+				parts = append(parts, inner[start:index])
+				start = index + 1
+			}
+		}
+	}
+	return append(parts, inner[start:])
+}
+
+// editorConfigNumericRange expands "n..m" into an alternation of the integers
+// in [n, m]. It returns ok=false when the body is not a numeric range.
+func editorConfigNumericRange(inner string) (string, bool, error) {
+	separator := strings.Index(inner, "..")
+	if separator < 0 {
+		return "", false, nil
+	}
+	low, err := strconv.Atoi(strings.TrimSpace(inner[:separator]))
+	if err != nil {
+		return "", false, nil
+	}
+	high, err := strconv.Atoi(strings.TrimSpace(inner[separator+2:]))
+	if err != nil {
+		return "", false, nil
+	}
+	if low > high {
+		low, high = high, low
+	}
+	const maxRangeSize = 65536
+	if high-low >= maxRangeSize {
+		return "", false, fmt.Errorf("editorconfig numeric range {%s} is too large", inner)
+	}
+	parts := make([]string, 0, high-low+1)
+	for value := low; value <= high; value++ {
+		parts = append(parts, strconv.Itoa(value))
+	}
+	return "(?:" + strings.Join(parts, "|") + ")", true, nil
 }
 
 func pathBase(path string) string {