Add caching for the Mill build tool

__tests__/cache.test.ts

@@ -201,6 +201,48 @@ describe('dependency cache', () => {
         expect(firstCall).not.toBe(thirdCall);
       });
     });
+    describe('for mill', () => {
+      it('throws error if no build.sc found', async () => {
+        await expect(restore('mill', '')).rejects.toThrow(
+          `No file in ${projectRoot(
+            workspace
+          )} matched to [**/build.sc,**/*.sc,**/mill,**/.mill-version,**/.config/mill-version], make sure you have checked out the target repository`
+        );
+      });
+      it('downloads cache', async () => {
+        createFile(join(workspace, 'build.sc'));
+
+        await restore('mill', '');
+        expect(spyCacheRestore).toHaveBeenCalled();
+        expect(spyGlobHashFiles).toHaveBeenCalledWith(
+          '**/build.sc\n**/*.sc\n**/mill\n**/.mill-version\n**/.config/mill-version'
+        );
+        expect(spyWarning).not.toHaveBeenCalled();
+        expect(spyInfo).toHaveBeenCalledWith('mill cache is not found');
+      });
+      it('detects scala and mill changes under **/mill-build/ folder', async () => {
+        createFile(join(workspace, 'build.sc'));
+        createDirectory(join(workspace, 'project'));
+        createFile(join(workspace, '.config/mill-version'));
+
+        await restore('mill', '');
+        const firstCall = spySaveState.mock.calls.toString();
+
+        spySaveState.mockClear();
+        await restore('mill', '');
+        const secondCall = spySaveState.mock.calls.toString();
+
+        // Make sure multiple restores produce the same cache
+        expect(firstCall).toBe(secondCall);
+
+        spySaveState.mockClear();
+        createFile(join(workspace, '.mill-version'));
+        await restore('mill', '');
+        const thirdCall = spySaveState.mock.calls.toString();
+
+        expect(firstCall).not.toBe(thirdCall);
+      });
+    });
     it('downloads cache based on versions.properties', async () => {
       createFile(join(workspace, 'versions.properties'));
 

__tests__/cache/mill/.gitignore

@@ -0,0 +1 @@
+out/

__tests__/cache/mill/.mill-version

@@ -0,0 +1 @@
+0.12.3

__tests__/cache/mill/build.sc

@@ -0,0 +1,12 @@
+package build
+import mill._, scalalib._
+
+object MyProject extends ScalaModule {
+    def scalaVersion = "2.13.11"
+    def ivyDeps = Agg(ivy"com.lihaoyi::mainargs:0.6.2")
+
+    object test extends ScalaTests {
+        def ivyDeps = Agg(ivy"com.lihaoyi::utest:0.8.5")
+        def testFramework = "utest.runner.Framework"
+    }
+}

__tests__/cache/mill/mill

@@ -0,0 +1,26 @@
+#!/usr/bin/env sh
+# This is a wrapper script that automatically downloads Mill from GitHub.
+set -e
+
+if [ -z "$MILL_VERSION" ] ; then
+    MILL_VERSION="$(head -n 1 .mill-version 2> /dev/null)"
+fi
+
+MILL_DOWNLOAD_PATH="$HOME/.cache/mill/download"
+MILL_EXEC_PATH="${MILL_DOWNLOAD_PATH}/$MILL_VERSION"
+
+if [ ! -x "$MILL_EXEC_PATH" ] ; then
+    mkdir -p "${MILL_DOWNLOAD_PATH}"
+    DOWNLOAD_FILE=$MILL_EXEC_PATH-tmp-download
+    MILL_DOWNLOAD_URL="https://github.com/lihaoyi/mill/releases/download/${MILL_VERSION%%-*}/$MILL_VERSION-assembly"
+    curl --fail -L -o "$DOWNLOAD_FILE" "$MILL_DOWNLOAD_URL"
+    chmod +x "$DOWNLOAD_FILE"
+    mv "$DOWNLOAD_FILE" "$MILL_EXEC_PATH"
+    unset DOWNLOAD_FILE
+    unset MILL_DOWNLOAD_URL
+fi
+
+unset MILL_DOWNLOAD_PATH
+unset MILL_VERSION
+
+exec "${MILL_EXEC_PATH}" "$@"