Verify Cabal functionality for various installs

This patch adds functionality to

* Test cabal build and cabal run in the CI workflow
* Test GHC 7.10.3 on Linux and ensures that it works
* On Linux, try hvr's PPA before ghcup

.github/workflows/workflow.yml

@@ -2,9 +2,10 @@ name: Main workflow
 on: [push]
 jobs:
   test:
-    name: Test ${{ matrix.os }}
+    name: Unit Tests - ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
         os: [ubuntu-latest, macOS-latest, windows-latest]
     steps:
@@ -17,9 +18,10 @@ jobs:
       - run: npm run pre-push
 
   install-haskell:
-    name: Test GHC Install ${{ matrix.os }}
+    name: GHC ${{ matrix.ghc }}, Cabal ${{ matrix.cabal }} - ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
         os: [ubuntu-latest, macOS-latest, windows-latest]
         ghc: ['8.8.3', '8.4.4']
@@ -33,7 +35,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - uses: actions/cache@v1
-        if: matrix.os  == 'macOS-latest' || matrix.ghc == '7.10.3'
+        if: matrix.os  == 'macOS-latest'
         with:
           path: ~/.ghcup
           key: ${{ runner.os }}-${{ matrix.ghc }}-ghcup
@@ -43,9 +45,11 @@ jobs:
           ghc-version: ${{ matrix.ghc }}
           cabal-version: ${{ matrix.cabal }}
       - run: runhaskell __tests__/hello.hs
+      - shell: bash
+        run: cd __tests__/project && cabal build && cabal run
 
   install-stack:
-    name: Test Stack Install ${{ matrix.os }}
+    name: Stack ${{ matrix.stack }} ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:

.gitignore

@@ -97,3 +97,5 @@ Thumbs.db
 # Ignore built ts files
 __tests__/runner/*
 lib/**/*
+
+dist-newstyle

__tests__/project/Main.hs

@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = putStrLn "Hello, Haskell!"

__tests__/project/Setup.hs

@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain

__tests__/project/project.cabal

@@ -0,0 +1,9 @@
+cabal-version:       >=1.10
+name:                project
+version:             0.1.0.0
+build-type:          Simple
+
+executable project
+  main-is:             Main.hs
+  build-depends:       base
+  default-language:    Haskell2010

dist/index.js

@@ -8640,21 +8640,33 @@ async function installStack(version) {
 exports.installStack = installStack;
 async function installTool(tool, version) {
     core.startGroup(`Installing ${tool}`);
-    // Currently only linux comes pre-installed with some versions of GHC.
-    // They're intalled to /opt. Let's see if we can save ourselves a download
+    // Linux comes pre-installed with some versions of GHC and supports older
+    // versions through hvr's PPA.
     if (process.platform === 'linux') {
         // Cabal is installed to /opt/cabal/x.x but cabal's full version is X.X.Y.Z
         const v = tool === 'cabal' ? version.slice(0, 3) : version;
+        const p = path_1.join('/opt', tool, v, 'bin');
+        const installed = await fs_1.promises
+            .access(p)
+            .then(() => true)
+            .catch(() => false);
+        if (tool === 'ghc' && !installed) {
+            try {
+                // hvr's PPA has better support for GHC < 8.0
+                await exec_1.exec(`sudo -- sh -c "apt-get -y install ghc-${v}"`);
+            }
+            catch {
+                // oh well, we tried
+            }
+        }
         try {
-            const p = path_1.join('/opt', tool, v, 'bin');
             await fs_1.promises.access(p);
-            core.debug(`Using pre-installed ${tool} ${version}`);
             core.addPath(p);
             core.endGroup();
             return;
         }
         catch {
-            // oh well, we tried
+            // ok, let's try the generic install now
         }
     }
     if (process.platform === 'win32') {

src/installer.ts

@@ -113,20 +113,34 @@ export async function installStack(version: string): Promise<void> {
 type Tool = 'cabal' | 'ghc';
 async function installTool(tool: Tool, version: string): Promise<void> {
   core.startGroup(`Installing ${tool}`);
-  // Currently only linux comes pre-installed with some versions of GHC.
-  // They're intalled to /opt. Let's see if we can save ourselves a download
+  // Linux comes pre-installed with some versions of GHC and supports older
+  // versions through hvr's PPA.
   if (process.platform === 'linux') {
     // Cabal is installed to /opt/cabal/x.x but cabal's full version is X.X.Y.Z
     const v = tool === 'cabal' ? version.slice(0, 3) : version;
+
+    const p = join('/opt', tool, v, 'bin');
+    const installed = await fs
+      .access(p)
+      .then(() => true)
+      .catch(() => false);
+
+    if (tool === 'ghc' && !installed) {
+      try {
+        // hvr's PPA has better support for GHC < 8.0
+        await exec(`sudo -- sh -c "apt-get -y install ghc-${v}"`);
+      } catch {
+        // oh well, we tried
+      }
+    }
+
     try {
-      const p = join('/opt', tool, v, 'bin');
       await fs.access(p);
-      core.debug(`Using pre-installed ${tool} ${version}`);
       core.addPath(p);
       core.endGroup();
       return;
     } catch {
-      // oh well, we tried
+      // ok, let's try the generic install now
     }
   }