Don't rely on git if .git isn't there during build (#4498)

If we don't have a `.git` directory during build, then don't try and run `git` commands to get e.g. history and last changed for policy files and changelog.

Closes #4497

etc/scripts/parsed_pug_file.js

@@ -12,33 +12,38 @@ const expectedHashes = {
     privacy: '014c73c485dd3625',
 };
 
-function execGit(command) {
+function _execGit(command) {
     const gitResult = execSync(command);
     if (!gitResult) {
         throw new Error(`Failed to execute ${command}`);
     }
     return gitResult.toString();
 }
 
-const gitChanges = execGit('git log --date=local --after="3 months ago" "--grep=(#[0-9]*)" --oneline')
-    .split('\n')
-    .map(line => line.match(/(?<hash>\w+) (?<description>.*)/))
-    .filter(x => x)
-    .map(match => match.groups);
-
 export default function(content) {
     const filePath = this.resourcePath;
     const filename = path.basename(filePath, '.pug');
+    const options = this.getOptions();
+    if (!options.useGit) {
+        this.emitWarning(new Error(`Running without git: file contents for ${filePath} will be wrong`));
+    }
+    const execGit = options.useGit ? _execGit : () => 'no-git-available';
     const lastTime = execGit(`git log -1 --format=%cd "${filePath}"`).trimEnd();
     const lastCommit = execGit(`git log -1 --format=%h "${filePath}"`).trimEnd();
+    const gitChanges = execGit('git log --date=local --after="3 months ago" "--grep=(#[0-9]*)" --oneline')
+        .split('\n')
+        .map(line => line.match(/(?<hash>\w+) (?<description>.*)/))
+        .filter(x => x)
+        .map(match => match.groups);
+
     const compiled = pug.compile(content.toString(), {filename: filePath});
 
     // When calculating the hash we ignore the hard-to-predict values like lastTime and lastCommit, else every time
     // we merge changes in policies to main we get a new hash after checking in, and that breaks the build.
     const htmlTextForHash = compiled({gitChanges, lastTime:'some-last-time', lastCommit:'some-last-commit'});
     const hashDigest = getHashDigest(htmlTextForHash, 'sha256', 'hex', 16);
     const expectedHash = expectedHashes[filename];
-    if (expectedHash !== undefined && expectedHash !== hashDigest) {
+    if (options.useGit && expectedHash !== undefined && expectedHash !== hashDigest) {
         this.emitError(
             new Error(
                 `Hash for file '${filePath}' changed from '${expectedHash}' to '${hashDigest}'` +

webpack.config.esm.js

@@ -22,6 +22,7 @@
 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 // POSSIBILITY OF SUCH DAMAGE.
 
+import fs from 'fs';
 import path from 'path';
 import {fileURLToPath} from 'url';
 
@@ -41,6 +42,7 @@ console.log(`webpack config for ${isDev ? 'development' : 'production'}.`);
 
 const distPath = path.resolve(__dirname, 'out', 'dist');
 const staticPath = path.resolve(__dirname, 'out', 'webpack', 'static');
+const hasGit = fs.existsSync(path.resolve(__dirname, '.git'));
 
 // Hack alert: due to a variety of issues, sometimes we need to change
 // the name here. Mostly it's things like webpack changes that affect
@@ -164,6 +166,9 @@ export default {
             {
                 test: /\.pug$/,
                 loader: './etc/scripts/parsed_pug_file.js',
+                options: {
+                    useGit: hasGit,
+                },
             },
             {
                 test: /\.ts$/,