Extend Gradle plugin to support Terraform fmt

plugin-gradle/README.md

@@ -69,6 +69,7 @@ Spotless supports all of Gradle's built-in performance features (incremental bui
   - [SQL](#sql) ([dbeaver](#dbeaver), [prettier](#prettier))
   - [Typescript](#typescript) ([tsfmt](#tsfmt), [prettier](#prettier))
   - [JSON](#json)
+  - [Terraform](#terraform)
   - Multiple languages
     - [Prettier](#prettier) ([plugins](#prettier-plugins), [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection))
       - javascript, jsx, angular, vue, flow, typescript, css, less, scss, html, json, graphql, markdown, ymaml
@@ -569,6 +570,36 @@ spotless {
 }
 ```
 
+## Terraform
+
+- `com.diffplug.gradle.spotless.TerraformExtension` [javadoc](https://javadoc.io/doc/com.diffplug.spotless/spotless-plugin-gradle/5.15.2/com/diffplug/gradle/spotless/TerraformExtension.html), [code](https://github.com/diffplug/spotless/blob/main/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/TerraformExtension.java)
+
+```gradle
+spotless {
+  terraform {
+    target 'src/**/*.tf', 'src/**/*.tfvars' // you have to set the target manually
+
+    fmt()  // has its own section below
+  }
+}
+```
+
+### fmt
+
+[homepage](https://www.terraform.io/docs/cli/commands/fmt.html). [changelog](https://github.com/hashicorp/terraform/blob/main/CHANGELOG.md).
+
+```gradle
+fmt('1.0.5') // version is optional
+
+// if the terraform cli is not on your path, you must specify its location manually
+fmt().pathToExe('/opt/homebrew/bin/terraform')
+// Spotless always checks the version of the terraform cli it is using
+// and will fail with an error if it does not match the expected version
+// (whether manually specified or default). If there is a problem, Spotless
+// will suggest commands to help install the correct version.
+//   TODO: handle installation & packaging automatically - https://github.com/diffplug/spotless/issues/674
+```
+
 <a name="applying-prettier-to-javascript--flow--typescript--css--scss--less--jsx--graphql--yaml--etc"></a>
 
 ## Prettier

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessExtension.java

@@ -175,6 +175,11 @@ public void json(Action<JsonExtension> closure) {
 		format(JsonExtension.NAME, JsonExtension.class, closure);
 	}
 
+	/** Configures the special terraform-specific extension for terraform files. */
+	public void terraform(Action<TerraformExtension> closure) {
+		format(TerraformExtension.NAME, TerraformExtension.class, closure);
+	}
+
 	/** Configures a custom extension. */
 	public void format(String name, Action<FormatExtension> closure) {
 		requireNonNull(name, "name");

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/TerraformExtension.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2021 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://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,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.gradle.spotless;
+
+import javax.inject.Inject;
+
+import com.diffplug.spotless.FormatterStep;
+import com.diffplug.spotless.terraform.TerraformFmtStep;
+
+public class TerraformExtension extends FormatExtension {
+	static final String NAME = "terraform";
+
+	@Inject
+	public TerraformExtension(SpotlessExtension spotless) {
+		super(spotless);
+	}
+
+	public TerraformFmtConfig fmt() {
+		return fmt(TerraformFmtStep.defaultVersion());
+	}
+
+	public TerraformFmtConfig fmt(String version) {
+		return new TerraformFmtConfig(version);
+	}
+
+	public class TerraformFmtConfig {
+		TerraformFmtStep stepCfg;
+
+		TerraformFmtConfig(String version) {
+			this.stepCfg = TerraformFmtStep.withVersion(version);
+			addStep(createStep());
+		}
+
+		public TerraformFmtConfig pathToExe(String pathToTerraformCli) {
+			stepCfg = stepCfg.withPathToExe(pathToTerraformCli);
+			replaceStep(createStep());
+			return this;
+		}
+
+		private FormatterStep createStep() {
+			return stepCfg.create();
+		}
+	}
+
+	@Override
+	protected void setupTask(SpotlessTask task) {
+		if (target == null) {
+			throw noDefaultTargetException();
+		}
+		super.setupTask(task);
+	}
+}