Add class for maintaining hie.yaml

If `hie.yaml` exists, install `implicit-hie` and update it with
`gen-hie` as part of the build. Next, we'll incorporate it into the
`on-dirty-files` check.

src/hie.ts

@@ -0,0 +1,47 @@
+import * as fs from "fs";
+import * as core from "@actions/core";
+
+import { StackCLI } from "./stack-cli";
+
+export const HIE_YAML: string = "hie.yaml";
+
+export class GenHIE {
+  public readonly path: string;
+
+  private readonly stack: StackCLI;
+  private readonly exists: boolean;
+  private installed: boolean;
+
+  constructor(stack: StackCLI, path?: string) {
+    this.stack = stack;
+    this.path = path ? path : HIE_YAML;
+    this.exists = fs.existsSync(this.path);
+    this.installed = false;
+  }
+
+  async install(): Promise<void> {
+    if (this.exists) {
+      try {
+        await this.stack.installCompilerTools(["implicit-hie"]);
+        this.installed = true;
+      } catch {
+        core.warning(
+          `Failed to install implicit-hie, ${this.path} will not be maintained`,
+        );
+      }
+    }
+  }
+
+  async generate(): Promise<void> {
+    if (this.exists && this.installed) {
+      const contents = await this.stack.read([
+        "exec",
+        "--",
+        "gen-hie",
+        "--stack",
+      ]);
+
+      fs.writeFileSync(this.path, contents);
+    }
+  }
+}

src/main.ts

@@ -7,6 +7,7 @@ import { hashProject } from "./hash-project";
 import { getInputs } from "./inputs";
 import { readStackYamlSync, getStackDirectories } from "./stack-yaml";
 import { DEFAULT_CACHE_OPTIONS, withCache } from "./with-cache";
+import { GenHIE } from "./hie";
 
 async function run() {
   try {
@@ -28,6 +29,7 @@ async function run() {
     }
 
     const stack = new StackCLI(inputs.stackArguments, core.isDebug());
+    const genHIE = new GenHIE(stack);
 
     await core.group("Install/upgrade stack", async () => {
       const installed = await stack.installed();
@@ -98,6 +100,7 @@ async function run() {
           await stack.setup(inputs.stackSetupArguments);
           await stack.buildDependencies(inputs.stackBuildArgumentsDependencies);
           await stack.installCompilerTools(inputs.compilerTools);
+          await genHIE.install();
         },
         {
           ...DEFAULT_CACHE_OPTIONS,
@@ -126,6 +129,10 @@ async function run() {
       );
     });
 
+    await core.group(`Maintain ${genHIE.path}`, async () => {
+      await genHIE.generate();
+    });
+
     await core.group("Check for dirty files", async () => {
       await checkDirtyFiles(inputs.onDirtyFiles);
     });