feat: multiple curly braces for watcher (#2068)

Allows doing something like this:

```caddyfile
watch "/app/{config,src}/*.{php,js}"
```

In the long term it would be nice to have pattern matching in the
watcher repo itself

internal/watcher/pattern.go

@@ -127,7 +127,7 @@ func (p *pattern) isValidPattern(fileName string) bool {
 
 	// if the pattern has size 1 we can match it directly against the filename
 	if len(p.parsedValues) == 1 {
-		return matchBracketPattern(p.parsedValues[0], fileNameWithoutDir)
+		return matchCurlyBracePattern(p.parsedValues[0], fileNameWithoutDir)
 	}
 
 	return p.matchPatterns(fileNameWithoutDir)
@@ -159,7 +159,7 @@ func (p *pattern) matchPatterns(fileName string) bool {
 			cursor = j
 			subPattern := strings.Join(partsToMatch[j:j+patternSize], string(filepath.Separator))
 
-			if matchBracketPattern(pattern, subPattern) {
+			if matchCurlyBracePattern(pattern, subPattern) {
 				cursor = j + patternSize - 1
 
 				break
@@ -174,24 +174,10 @@ func (p *pattern) matchPatterns(fileName string) bool {
 	return true
 }
 
-// we also check for the following bracket syntax: /path/*.{php,twig,yaml}
-func matchBracketPattern(pattern string, fileName string) bool {
-	openingBracket := strings.Index(pattern, "{")
-	closingBracket := strings.Index(pattern, "}")
-
-	// if there are no brackets we can match regularly
-	if openingBracket == -1 || closingBracket == -1 {
-		return matchPattern(pattern, fileName)
-	}
-
-	beforeTheBrackets := pattern[:openingBracket]
-	betweenTheBrackets := pattern[openingBracket+1 : closingBracket]
-	afterTheBrackets := pattern[closingBracket+1:]
-
-	// all bracket entries are checked individually, only one needs to match
-	// *.{php,twig,yaml} -> *.php, *.twig, *.yaml
-	for pattern := range strings.SplitSeq(betweenTheBrackets, ",") {
-		if matchPattern(beforeTheBrackets+pattern+afterTheBrackets, fileName) {
+// we also check for the following syntax: /path/*.{php,twig,yaml}
+func matchCurlyBracePattern(pattern string, fileName string) bool {
+	for _, subPattern := range expandCurlyBraces(pattern) {
+		if matchPattern(subPattern, fileName) {
 			return true
 		}
 	}
@@ -199,6 +185,26 @@ func matchBracketPattern(pattern string, fileName string) bool {
 	return false
 }
 
+// {dir1,dir2}/path -> []string{"dir1/path", "dir2/path"}
+func expandCurlyBraces(s string) []string {
+	before, rest, found := strings.Cut(s, "{")
+	if !found {
+		return []string{s}
+	}
+
+	inside, after, found := strings.Cut(rest, "}")
+	if !found {
+		return []string{s} // no closing brace
+	}
+
+	var out []string
+	for _, subPattern := range strings.Split(inside, ",") {
+		out = append(out, expandCurlyBraces(before+subPattern+after)...)
+	}
+
+	return out
+}
+
 func matchPattern(pattern string, fileName string) bool {
 	if pattern == "" {
 		return true

internal/watcher/pattern_test.go

@@ -259,7 +259,7 @@ func TestInvalidDirectoryPatterns(t *testing.T) {
 	}
 }
 
-func TestValidExtendedPatterns(t *testing.T) {
+func TestValidCurlyBracePatterns(t *testing.T) {
 	data := []struct {
 		pattern string
 		dir     string
@@ -272,6 +272,10 @@ func TestValidExtendedPatterns(t *testing.T) {
 		{"/path/{dir1,dir2}/file.php", "/path/dir2/file.php"},
 		{"/app/{app,config,resources}/**/*.php", "/app/app/subpath/file.php"},
 		{"/app/{app,config,resources}/**/*.php", "/app/config/subpath/file.php"},
+		{"/path/{dir1,dir2}/{a,b}{a,b}.php", "/path/dir1/ab.php"},
+		{"/path/{dir1,dir2}/{a,b}{a,b}.php", "/path/dir2/aa.php"},
+		{"/path/{dir1,dir2}/{a,b}{a,b}.php", "/path/dir2/bb.php"},
+		{"/path/{dir1/test.php,dir2/test.php}", "/path/dir1/test.php"},
 	}
 
 	for _, d := range data {
@@ -283,7 +287,7 @@ func TestValidExtendedPatterns(t *testing.T) {
 	}
 }
 
-func TestInvalidExtendedPatterns(t *testing.T) {
+func TestInvalidCurlyBracePatterns(t *testing.T) {
 	data := []struct {
 		pattern string
 		dir     string
@@ -293,6 +297,9 @@ func TestInvalidExtendedPatterns(t *testing.T) {
 		{"/path/{file.php,file.twig}", "/path/file.txt"},
 		{"/path/{dir1,dir2}/file.php", "/path/dir3/file.php"},
 		{"/path/{dir1,dir2}/**/*.php", "/path/dir1/subpath/file.txt"},
+		{"/path/{dir1,dir2}/{a,b}{a,b}.php", "/path/dir1/ac.php"},
+		{"/path/{}/{a,b}{a,b}.php", "/path/dir1/ac.php"},
+		{"/path/}dir{/{a,b}{a,b}.php", "/path/dir1/aa.php"},
 	}
 
 	for _, d := range data {