feat(75): provide access to prior state resources if available

.gitignore

@@ -159,3 +159,7 @@ override.tf.json
 
 # Include tfplan files to ignore the plan output of command: terraform plan -out=tfplan
 # example: *tfplan*
+
+# Ignore IDE configuration files
+**/.idea/*
+**/.vscode/*

test/fixtures/plan_output.json

@@ -95,7 +95,25 @@
   },
   "prior_state": {
     "format_version": "0.1",
-    "terraform_version": "0.12.6"
+    "terraform_version": "0.12.6",
+    "values": {
+      "root_module": {
+        "resources": [
+          {
+            "address": "data.google_client_config.current",
+            "mode": "data",
+            "type": "google_client_config",
+            "name": "current",
+            "provider_name": "registry.terraform.io/hashicorp/google",
+            "schema_version": 0,
+            "values": {
+              "description": "foo-value"
+            },
+            "sensitive_values": {}
+          }
+        ]
+      }
+    }
   },
   "configuration": {
     "provider_config": {

test/fixtures/plan_output_no_prior.json

@@ -0,0 +1,103 @@
+{
+  "format_version": "0.1",
+  "terraform_version": "0.12.6",
+  "variables": {
+    "foo": {
+      "value": "bar"
+    }
+  },
+  "planned_values": {
+    "outputs": {
+      "spam": {
+        "sensitive": false,
+        "value": "baz"
+      }
+    },
+    "root_module": {
+      "resources": [
+        {
+          "address": "spam.somespam",
+          "mode": "managed",
+          "type": "spam",
+          "name": "somespam",
+          "provider_name": "dummy",
+          "schema_version": 0,
+          "values": {
+            "spam-value": "spam"
+          }
+        }
+      ],
+      "child_modules": [
+        {
+          "address": "module.parent",
+          "resources": [
+            {
+              "address": "module.parent.foo.somefoo",
+              "type": "foo",
+              "name": "somefoo",
+              "provider_name": "dummy",
+              "values": {
+                "foo-value": "foo"
+              }
+            }
+          ],
+          "child_modules": [
+            {
+              "address": "module.parent.module.child",
+              "resources": [
+                {
+                  "address": "module.parent.module.child.eggs.someeggs",
+                  "type": "eggs",
+                  "name": "someeggs",
+                  "provider_name": "dummy",
+                  "values": {
+                    "eggs-value": "eggs"
+                  }
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    }
+  },
+  "resource_changes": [
+    {
+      "address": "module.resource-change.foo_resource.somefoo",
+      "module_address": "module.resource-change",
+      "mode": "managed",
+      "type": "foo-resource",
+      "name": "somefoo",
+      "provider_name": "dummy",
+      "change": {
+        "actions": [
+          "create"
+        ],
+        "before": null,
+        "after": {
+          "foo": "foo-value"
+        },
+        "after_unknown": {
+          "eggs": true
+        }
+      }
+    }
+  ],
+  "output_changes": {
+    "spam": {
+      "actions": [
+        "create"
+      ],
+      "before": null,
+      "after": "bar",
+      "after_unknown": false
+    }
+  },
+  "configuration": {
+    "provider_config": {
+      "google": {
+        "name": "google"
+      }
+    }
+  }
+}

test/test_plan.py

@@ -4,7 +4,7 @@
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
-#     https://www.apache.org/licenses/LICENSE-2.0
+#   https://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ -25,6 +25,13 @@ def plan_out(fixtures_dir):
     return tftest.TerraformPlanOutput(json.load(fp))
 
 
+@pytest.fixture(scope="module")
+def plan_out_no_prior(fixtures_dir):
+  import json
+  with open('%s/plan_output_no_prior.json' % fixtures_dir) as fp:
+    return tftest.TerraformPlanOutput(json.load(fp))
+
+
 def test_output_attributes(plan_out):
   assert plan_out.format_version == "0.1"
   assert plan_out.terraform_version == "0.12.6"
@@ -86,3 +93,15 @@ def test_plan_stdout(fixtures_dir):
   tf = tftest.TerraformTest('plan_no_resource_changes', fixtures_dir)
   result = tf.plan(output=False)
   assert 'just_an_output = "Hello, plan!"' in result
+
+
+def test_plan_prior_state(plan_out):
+  prior_resources = plan_out.prior_resources()
+  assert len(prior_resources) == 1
+  assert prior_resources['data.google_client_config.current']['type'] == 'google_client_config'
+  assert prior_resources['data.google_client_config.current']['values']['description'] == 'foo-value'
+
+
+def test_plan_no_prior_state(plan_out_no_prior):
+  prior_resources = plan_out_no_prior.prior_resources()
+  assert not prior_resources

tftest.py

@@ -242,6 +242,9 @@ def __init__(self, raw):
     # there might be no variables defined
     self.variables = TerraformValueDict(raw.get('variables', {}))
 
+    prior_state = raw.get('prior_state', {})
+    values = prior_state.get('values', {})
+    self.prior_root_module = TerraformPlanModule(values.get('root_module', {}))
   @property
   def resources(self):
     return self.root_module.resources
@@ -250,6 +253,9 @@ def resources(self):
   def modules(self):
     return self.root_module.child_modules
 
+  def prior_resources(self):
+    return self.prior_root_module.resources
+
   def __getattr__(self, name):
     return self._raw[name]