tests: cycles in environment variables are detected and gracefully ha…

…ndled

tests/data/circular.yaml

@@ -7,8 +7,11 @@ trees:
     path: ${GARDEN_CONFIG_DIR}
     variables:
       root-variable: root-tree-${circular-variable}
+    environment:
+      ENV_CIRCULAR_VARIABLE: ${TREE_NAME}/${env-circular-variable}
 
 # This file contains circular dependencies in variables.
 variables:
   circular-variable: ${graft::circular-variable}
   root-variable: root-${circular-variable}
+  env-circular-variable: variables/${ENV_CIRCULAR_VARIABLE}

tests/data/grafts/graft-circular.yaml

@@ -5,3 +5,5 @@ variables:
 trees:
   current:
     path: ${GARDEN_CONFIG_DIR}
+    environment:
+      ENV_CIRCULAR_VARIABLE: graft/${TREE_NAME}/${env-circular-variable}

tests/integration_test.rs

@@ -1009,6 +1009,33 @@ fn eval_graft_variables_with_circular_dependencies() {
     assert_eq!(output, "root-graft-");
 }
 
+/// Test evaluating a graft variable that triggers an infinite loop via a circular dependency.
+#[test]
+fn eval_environment_variables_with_circular_dependencies() {
+    // The graft's environment variable has "graft/${TREE_NAME}/${circular-variable}".
+    // The ${env-circular-variable} expression is "variables/${ENV_CIRCULAR_VARIABLE}"
+    // The evaluation machinery is short-circuits itself on the inner ${env-circular-variable}
+    // and resolves down until the cycle is detected and gets cut off.
+    // The graft::current tree is called "current".
+    let output = garden_capture(&[
+        "--config",
+        "tests/data/circular.yaml",
+        "eval",
+        "${ENV_CIRCULAR_VARIABLE}",
+        "graft::current",
+    ]);
+    assert_eq!(output, "graft/current/variables/graft/current/");
+    // The root-tree's context traverses in a different order and evaluates its TREE_NAME.
+    let output = garden_capture(&[
+        "--config",
+        "tests/data/circular.yaml",
+        "eval",
+        "${ENV_CIRCULAR_VARIABLE}",
+        "root-tree",
+    ]);
+    assert_eq!(output, "root-tree/variables/root-tree/");
+}
+
 /// `garden grow` creates symlinks
 #[test]
 #[named]