add gitCatFile for getting file contents without git checkouts, #355

Signed-off-by: Michael Kauzmann <[email protected]>

js/common/ReleaseBranch.js

@@ -23,6 +23,7 @@ const getBranchVersion = require( './getBranchVersion' );
 const getFileAtBranch = require( './getFileAtBranch' );
 const getRepoVersion = require( './getRepoVersion' );
 const gitCheckout = require( './gitCheckout' );
+const gitCatFile = require( './gitCatFile' );
 const gitCheckoutDirectory = require( './gitCheckoutDirectory' );
 const gitCloneOrFetchDirectory = require( './gitCloneOrFetchDirectory' );
 const gitFirstDivergingCommit = require( './gitFirstDivergingCommit' );
@@ -611,18 +612,14 @@ module.exports = ( function() {
      * @returns {Promise.<boolean>}
      */
     async usesChipper2() {
-      await gitCheckout( this.repo, this.branch );
-      const dependencies = await getDependencies( this.repo );
-      await gitCheckout( 'chipper', dependencies.chipper.sha );
 
-      const chipperVersion = ChipperVersion.getFromRepository();
+      // TODO: use better functions once we convert getDependencies and getPackageJSON, https://github.com/phetsims/perennial/issues/355
+      const dependencies = JSON.parse( await gitCatFile( this.repo, 'dependencies.json', this.branch ) );
 
-      const result = chipperVersion.major !== 0 || chipperVersion.minor !== 0;
+      const chipperPackageJSON = JSON.parse( await gitCatFile( 'chipper', 'package.json', dependencies.chipper.sha ) );
+      const chipperVersion = ChipperVersion.getFromPackageJSON( chipperPackageJSON );
 
-      await gitCheckout( this.repo, 'main' );
-      await gitCheckout( 'chipper', 'main' );
-
-      return result;
+      return chipperVersion.major !== 0 || chipperVersion.minor !== 0;
     }
 
     /**

js/common/gitCatFile.js

@@ -0,0 +1,30 @@
+// Copyright 2017, University of Colorado Boulder
+
+/**
+ * retrieve the contents of a file without changing the git tree via checkouts.
+ *
+ * @author Michael Kauzmann (PhET Interactive Simulations)
+ * @author Jonathan Olson <[email protected]>
+ */
+
+const assert = require( 'assert' );
+const execute = require( './execute' );
+
+/**
+ * Gets the contents of the file at a given state in the git tree
+ * @public
+ *
+ * @param {string} repo - The repository name
+ * @param {string} file - Path to the file from the repo root, like js/myFile.js
+ * @param {string} branchOrSha - what revision to get the contents of the file at. "buoyancy-1.0" or "main" or
+ *                               "{{SHA}}". Defaults to the current checkout (HEAD)
+ * @returns {Promise.<string>} - Stdout
+ * @rejects {ExecuteError}
+ */
+module.exports = async function gitCatFile( repo, file, branchOrSha = 'HEAD' ) {
+  assert( typeof repo === 'string' );
+  assert( typeof file === 'string' );
+  assert( typeof branchOrSha === 'string' );
+
+  return execute( 'git', [ 'cat-file', 'blob', `${branchOrSha}:${file}` ], `../${repo}` );
+};