httpcaddyfile: Improve error on matcher declared outside site block (#3431)

caddyconfig/httpcaddyfile/httptype.go

@@ -54,6 +54,9 @@ func (st ServerType) Setup(inputServerBlocks []caddyfile.ServerBlock,
 	originalServerBlocks := make([]serverBlock, 0, len(inputServerBlocks))
 	for i, sblock := range inputServerBlocks {
 		for j, k := range sblock.Keys {
+			if j == 0 && strings.HasPrefix(k, "@") {
+				return nil, warnings, fmt.Errorf("cannot define a matcher outside of a site block: '%s'", k)
+			}
 			if _, ok := sbKeys[k]; ok {
 				return nil, warnings, fmt.Errorf("duplicate site address not allowed: '%s' in %v (site block %d, key %d)", k, sblock.Keys, i, j)
 			}

caddyconfig/httpcaddyfile/httptype_test.go

@@ -57,6 +57,15 @@ func TestMatcherSyntax(t *testing.T) {
 			expectWarn:  false,
 			expectError: false,
 		},
+		{
+			input: `@matcher {
+				path /matcher-not-allowed/outside-of-site-block/*
+			}
+			http://localhost
+			`,
+			expectWarn:  false,
+			expectError: true,
+		},
 	} {
 
 		adapter := caddyfile.Adapter{