Bring back v2 rule matchers

integration/fixtures/k8s/01-traefik-crd.yml

@@ -195,6 +195,10 @@ spec:
                         - name
                         type: object
                       type: array
+                    syntax:
+                      description: 'Syntax defines the router''s rule syntax. More
+                        info: https://doc.traefik.io/traefik/v3.0/routing/routers/#rulesyntax'
+                      type: string
                   required:
                   - kind
                   - match
@@ -402,6 +406,10 @@ spec:
                         - port
                         type: object
                       type: array
+                    syntax:
+                      description: 'Syntax defines the router''s rule syntax. More
+                        info: https://doc.traefik.io/traefik/v3.0/routing/routers/#rulesyntax_1'
+                      type: string
                   required:
                   - match
                   type: object

integration/fixtures/with_default_rule_syntax.toml

@@ -0,0 +1,41 @@
+[global]
+  checkNewVersion = false
+  sendAnonymousUsage = false
+
+[core]
+  defaultRuleSyntax = "v2"
+
+[log]
+  level = "DEBUG"
+  noColor = true
+
+[entryPoints]
+  [entryPoints.web]
+    address = ":8000"
+
+[api]
+  insecure = true
+
+[providers.file]
+  filename = "{{ .SelfFilename }}"
+
+## dynamic configuration ##
+
+[http.routers]
+  [http.routers.router1]
+    service = "service1"
+    rule = "PathPrefix(`/foo`, `/bar`)"
+
+  [http.routers.router2]
+    service = "service1"
+    rule = "QueryRegexp(`foo`, `bar`)"
+
+  [http.routers.router3]
+    service = "service1"
+    rule = "PathPrefix(`/foo`, `/bar`)"
+    ruleSyntax = "v3"
+
+[http.services]
+  [http.services.service1]
+    [http.services.service1.loadBalancer]
+      [http.services.service1.loadBalancer.servers]

integration/fixtures/without_default_rule_syntax.toml

@@ -0,0 +1,38 @@
+[global]
+  checkNewVersion = false
+  sendAnonymousUsage = false
+
+[log]
+  level = "DEBUG"
+  noColor = true
+
+[entryPoints]
+  [entryPoints.web]
+    address = ":8000"
+
+[api]
+  insecure = true
+
+[providers.file]
+  filename = "{{ .SelfFilename }}"
+
+## dynamic configuration ##
+
+[http.routers]
+  [http.routers.router1]
+    service = "service1"
+    rule = "PathPrefix(`/foo`) || PathPrefix(`/bar`)"
+
+  [http.routers.router2]
+    service = "service1"
+    rule = "PathPrefix(`/foo`, `/bar`)"
+
+  [http.routers.router3]
+    service = "service1"
+    rule = "QueryRegexp(`foo`, `bar`)"
+    ruleSyntax = "v2"
+
+[http.services]
+  [http.services.service1]
+    [http.services.service1.loadBalancer]
+      [http.services.service1.loadBalancer.servers]