fix(core): use file full path in git show

Use file full path in git show to identify affected files to fix an issue when nx workspace is not at the root of git repository

Closes #2292

packages/workspace/src/core/file-utils.ts

@@ -1,7 +1,7 @@
 import * as path from 'path';
 import * as fs from 'fs';
 import { appRootPath } from '../utils/app-root';
-import { extname } from 'path';
+import {extname, relative} from 'path';
 import { jsonDiff } from '../utils/json-diff';
 import { readFileSync } from 'fs';
 import { execSync } from 'child_process';
@@ -89,9 +89,12 @@ function defaultReadFileAtRevision(
   revision: void | string
 ): string {
   try {
+    const fileFullPath = `${appRootPath}/${file}`;
+    const gitRepositoryPath = execSync('git rev-parse --show-toplevel').toString().trim();
+    const filePathInGitRepository = relative(gitRepositoryPath, fileFullPath);
     return !revision
       ? readFileSync(file).toString()
-      : execSync(`git show ${revision}:${file}`, {
+      : execSync(`git show ${revision}:${filePathInGitRepository}`, {
           maxBuffer: TEN_MEGABYTES
         })
           .toString()