feat(requires): support variable references in enum constraints (#2678)

testdata/requires/Taskfile.yml

@@ -1,5 +1,9 @@
 version: '3'
 
+vars:
+  ALLOWED_ENVS: ["dev", "staging", "prod"]
+  NOT_A_LIST: "this is a string"
+
 tasks:
   default:
     - task: missing-var
@@ -41,3 +45,27 @@ tasks:
       {{range .MY_VAR | splitList " " }}
         echo {{.}}
       {{end}}
+
+  validation-var-ref:
+    requires:
+      vars:
+        - name: ENV
+          enum:
+            ref: .ALLOWED_ENVS
+    cmd: echo "{{.ENV}}"
+
+  validation-var-ref-invalid:
+    requires:
+      vars:
+        - name: VALUE
+          enum:
+            ref: .NOT_A_LIST
+    cmd: echo "{{.VALUE}}"
+
+  validation-var-ref-nonexistent:
+    requires:
+      vars:
+        - name: ENV
+          enum:
+            ref: .NONEXISTENT_VAR
+    cmd: echo "{{.ENV}}"

testdata/requires/testdata/TestRequires-enum_ref_-_fails_validation-err-run.golden

@@ -0,0 +1,2 @@
+task: Task "validation-var-ref" cancelled because it is missing required variables:
+  - ENV has an invalid value : 'invalid' (allowed values : [dev staging prod])

testdata/requires/testdata/TestRequires-enum_ref_-_passes_validation.golden

@@ -0,0 +1,2 @@
+task: [validation-var-ref] echo "dev"
+dev

testdata/requires/testdata/TestRequires-enum_ref_-_ref_to_non-list-err-run.golden

@@ -0,0 +1 @@
+enum reference ".NOT_A_LIST" must resolve to a list

testdata/requires/testdata/TestRequires-enum_ref_-_ref_to_nonexistent_var-err-run.golden

@@ -0,0 +1 @@
+enum reference ".NONEXISTENT_VAR" must resolve to a list