Fix output only plan from causing parse error

CHANGELOG.md

@@ -3,6 +3,27 @@
 All notable changes to this project will be documented in this file. The format is based on [Keep a Changelog](http://keepachangelog.com/).
 > Sections: (`Added`, `Changed`, `Deprecated`, `Removed`, `Fixed`, `Security`)
 
+## [1.3.6] - 2022-01-28
+
+### Fixed
+- Prevent parsing error when an empty plan is generated for Terraform 0.13+ where there is an output-only change.
+  > Example output of a plan:
+  > ```
+  > # aws_lambda_function.default has been changed
+  > ~ resource "aws_lambda_function" "default" {
+  >       # (2 unchanged blocks hidden)
+  >   }
+  >
+  > Unless you have made equivalent changes to your configuration, or ignored the
+  > relevant attributes using ignore_changes, the following plan may include
+  > actions to undo or respond to these changes.
+  > 
+  > ─────────────────────────────────────────────────────────────────────────────
+  > 
+  > Changes to Outputs:
+  >   ~ lambda_source_code_size = 100 -> 101
+  > ```
+
 ## [1.3.4] - 2022-01-13
 
 ### Fixed

src/Terraform12OutputParser.php

@@ -1,6 +1,6 @@
 <?php
 /**
- * @copyright (c) 2019 Steve Kluck
+ * @copyright (c) 2022 Steve Kluck
  *
  * For full license information, please view the LICENSE distributed with this source code.
  */
@@ -19,6 +19,7 @@ class Terraform12OutputParser
     const NO_CHANGES_STRING = "\nNo changes. Infrastructure is up-to-date.\n";
     # New in Terraform 0.13+
     const NO_CHANGES_STRING_ALT = "\nNo changes. Your infrastructure matches the configuration.\n";
+    const NO_CHANGES_OUTPUT_ONLY = "\nYou can apply this plan to save these new output values to the Terraform\nstate, without changing any real infrastructure.\n";
 
     const CONTENT_START_STRING = "\nTerraform will perform the following actions:\n";
     const CONTENT_END_STRING = "\nPlan:";
@@ -85,15 +86,7 @@ public function parse(string $input): array
         $input = $this->stripANSICodes($input);
         $input = $this->sanitizeWindowsLineEndings($input);
 
-        if (strpos($input, self::NO_CHANGES_STRING) !== false) {
-            return [
-                'errors' => $this->errors(),
-                'changedResources' => [],
-                'modules' => [],
-            ];
-        }
-
-        if (strpos($input, self::NO_CHANGES_STRING_ALT) !== false) {
+        if ($this->isNoChangesPlan($input)) {
             return [
                 'errors' => $this->errors(),
                 'changedResources' => [],
@@ -373,6 +366,30 @@ private function parseUsedModules($input)
         return $modules;
     }
 
+    /**
+     * @param string $input
+     *
+     * @return bool
+     */
+    private function isNoChangesPlan($input)
+    {
+        if (strpos($input, self::NO_CHANGES_STRING) !== false) {
+            return true;
+        }
+
+        // Terraform 0.13+ where absolutely no changes (not even to outputs)
+        if (strpos($input, self::NO_CHANGES_STRING_ALT) !== false) {
+            return true;
+        }
+
+        // Terraform 0.13+ where output only changes (may have "changes outside of terraform")
+        if (strpos($input, self::NO_CHANGES_OUTPUT_ONLY) !== false) {
+            return true;
+        }
+
+        return false;
+    }
+
     /**
      * @param string $input
      *

tests/.fixtures-1.0/86-output-only-changes.expected.json

@@ -0,0 +1,5 @@
+{
+    "errors": [],
+    "changedResources": [],
+    "modules": []
+}

tests/.fixtures-1.0/86-output-only-changes.stdout.txt

@@ -0,0 +1,49 @@
+Note: Objects have changed outside of Terraform
+
+Terraform detected the following changes made outside of Terraform since the
+last "terraform apply":
+
+  # aws_lambda_function.default has been changed
+  ~ resource "aws_lambda_function" "default" {
+        id                             = "prod-123456-myservice"
+      ~ last_modified                  = "2022-01-26T01:40:57.000+0000" -> "2022-01-26T14:31:40.000+0000"
+      ~ source_code_size               = 2830 -> 2397
+        tags                           = {
+            "app-id"                        = "123456"
+            "environment"                   = "prod"
+            "iac"                           = "terraform"
+        }
+        # (17 unchanged attributes hidden)
+
+      + environment {
+          + variables = {
+              + "ExampleVar" = "myenvvar"
+            }
+        }
+
+
+        # (2 unchanged blocks hidden)
+    }
+
+Unless you have made equivalent changes to your configuration, or ignored the
+relevant attributes using ignore_changes, the following plan may include
+actions to undo or respond to these changes.
+
+─────────────────────────────────────────────────────────────────────────────
+
+Changes to Outputs:
+  ~ lambda_source_code_size = 2830 -> 2397
+
+You can apply this plan to save these new output values to the Terraform
+state, without changing any real infrastructure.
+╷
+│ Warning: Version constraints inside provider configuration blocks are deprecated
+│ 
+│   on .terraform/modules/lambda_iam_module/modules/lambda-iam/main.tf line 3, in provider "aws":
+│    3:   version = "~> 3.20"
+│ 
+│ Terraform 0.13 and earlier allowed provider version constraints inside the
+│ provider configuration block, but that is now deprecated and will be
+│ removed in a future version of Terraform. To silence this warning, move the
+│ provider version constraint into the required_providers block.
+╵

tests/Terraform10OutputParserTest.php

@@ -30,6 +30,7 @@ public function providerTestCases()
             'nochanges'            => '83-nochanges',
             'resource-comment'     => '84-resource-comment',
             'debug-output'         => '85-debug-output',
+            'output-only-changes'  => '86-output-only-changes',
         ];
 
         return array_map(function ($case) use ($fixturesDir) {