fix git.bzl error when outputRoot is in a git repo

`_clone_or_update()` should `git clone` external repositories only if repo is absent. Unfortunately, it may happen that the bazel outputRoot (~/.cache/bazel by default) is a subdirectory of some other git working copy. For example, user may track his whole home directory in git and add `.config` to .gitignore. In that case, it is not enough to check if the cache dir is a git repo. One must check that the cache dir holds a root of a git working copy. In other words, the `.git` folder must be in the repo dir, not on any level above.

* Steps to reproduce
    ```bash
    cd ~/.cache
    git init
    cd /some/project/that/uses/bazel-git_repository
    mv WORKSPACE WORKSPACE.orig
    (echo "load('@bazel_tools//tools/build_defs/repo:git.bzl', 'git_repository')" ; cat WORKSPACE.orig) > WORKSPACE
    bazel --batch build :all || echo "Ah, there is a bug"
    ```

Read on for definitive info.

* clone any project that uses `git_repository`
    ```bash
    [arch@archlinux bazelbuild]$ git clone https://github.com/bazelbuild/bazel-watcher.git
    [arch@archlinux bazelbuild]$ cd bazel-watcher
    ```

* enable Skylark implementation of `git_repository` as documented in https://github.com/bazelbuild/bazel/issues/1408#issuecomment-276815467
    ```bash
    [arch@archlinux bazel-watcher]$ mv WORKSPACE WORKSPACE.orig
    [arch@archlinux bazel-watcher]$ (echo "load('@bazel_tools//tools/build_defs/repo:git.bzl', 'git_repository')" ; cat WORKSPACE.orig) > WORKSPACE
    [arch@archlinux bazel-watcher]$ grep -v ^# WORKSPACE |head -n4
    load('@bazel_tools//tools/build_defs/repo:git.bzl', 'git_repository')

    git_repository(
        name = "com_github_bazelbuild_bazel_integration_testing",
    ```

* (optionally) define custom Bazel `outputRoot` directory (default is ~/.cache/bazel)
    ```bash
    [arch@archlinux bazel-watcher]$ rm -rf /tmp/.cache/ ; mkdir /tmp/.cache/
    [arch@archlinux bazel-watcher]$ export TEST_TMPDIR=/tmp/.cache/bazel
    ```

* try building the project to make sure everything works as expected
    ```bash
    [arch@archlinux bazel-watcher]$ bazel --batch build :all
    INFO: $TEST_TMPDIR defined: output root default is '/tmp/.cache/bazel' and max_idle_secs default is '15'.
    Extracting Bazel installation...
    WARNING: /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing/WORKSPACE:1: Workspace name in /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing/WORKSPACE (@build_bazel_integration_testing) does not match the name given in the repository's definition (@com_github_bazelbuild_bazel_integration_testing); this will cause a build error in future versions
    INFO: Analysed target //:go_prefix (6 packages loaded).
    INFO: Found 1 target...
    Target //:go_prefix up-to-date (nothing to build)
    INFO: Elapsed time: 15.088s, Critical Path: 0.05s
    INFO: Build completed successfully, 1 total action
    [arch@archlinux bazel-watcher]$ echo $?
    0
    ```

* reproduce the issue by placing the `outputRoot` under a git working copy
    ```bash
    [arch@archlinux bazel-watcher]$ rm -rf /tmp/.cache/ ; mkdir /tmp/.cache/
    [arch@archlinux bazel-watcher]$ cd /tmp/.cache/ ; git init
    Initialized empty Git repository in /tmp/.cache/.git/
    [arch@archlinux .cache]$ cd -
    [arch@archlinux bazel-watcher]$ bazel --batch build :all
    INFO: $TEST_TMPDIR defined: output root default is '/tmp/.cache/bazel' and max_idle_secs default is '15'.
    Extracting Bazel installation...
    ERROR: error loading package '': Encountered error while reading extension file 'tools/repositories.bzl': no such package '@com_github_bazelbuild_bazel_integration_testing//tools': Traceback (most recent call last):
        File "/tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl", line 69
            _clone_or_update(ctx)
        File "/tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl", line 44, in _clone_or_update
            fail(("error cloning %s:\n%s" % (ctx....)))
    error cloning com_github_bazelbuild_bazel_integration_testing:
    + cd /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external
    + cd /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing
    + git reset --hard 55a6a70dbcc2cc7699ee715746fb1452788f8d3c
    fatal: Could not parse object '55a6a70dbcc2cc7699ee715746fb1452788f8d3c'.
    + git fetch origin 55a6a70dbcc2cc7699ee715746fb1452788f8d3c:55a6a70dbcc2cc7699ee715746fb1452788f8d3c
    fatal: 'origin' does not appear to be a git repository
    fatal: Could not read from remote repository.

    Please make sure you have the correct access rights
    and the repository exists.
    ERROR: error loading package '': Encountered error while reading extension file 'tools/repositories.bzl': no such package '@com_github_bazelbuild_bazel_integration_testing//tools': Traceback (most recent call last):
        File "/tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl", line 69
            _clone_or_update(ctx)
        File "/tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl", line 44, in _clone_or_update
            fail(("error cloning %s:\n%s" % (ctx....)))
    error cloning com_github_bazelbuild_bazel_integration_testing:
    + cd /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external
    + cd /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing
    + git reset --hard 55a6a70dbcc2cc7699ee715746fb1452788f8d3c
    fatal: Could not parse object '55a6a70dbcc2cc7699ee715746fb1452788f8d3c'.
    + git fetch origin 55a6a70dbcc2cc7699ee715746fb1452788f8d3c:55a6a70dbcc2cc7699ee715746fb1452788f8d3c
    fatal: 'origin' does not appear to be a git repository
    fatal: Could not read from remote repository.

    Please make sure you have the correct access rights
    and the repository exists.
    INFO: Elapsed time: 4.974s
    FAILED: Build did NOT complete successfully (0 packages loaded)
    ```

* let's find out why it failed
    ```bash
    [arch@archlinux bazel-watcher]$ grep rev-parse /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl
        if ! ( cd '{dir}' && git rev-parse --git-dir ) >/dev/null 2>&1; then
    [arch@archlinux bazel-watcher]$ cd /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing
    [arch@archlinux com_github_bazelbuild_bazel_integration_testing]$ git rev-parse --git-dir
    /tmp/.cache/.git
    [arch@archlinux com_github_bazelbuild_bazel_integration_testing]$ cd -
    ```

* let's fix git.bzl
    ```bash
    [arch@archlinux bazel-watcher]$ sed -i -E 's/git rev-parse --git-dir/[[ "$(git rev-parse --git-dir)" == '.git' ]]/' /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl
    [arch@archlinux bazel-watcher]$ grep rev-parse /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/bazel_tools/tools/build_defs/repo/git.bzl
    if ! ( cd '{dir}' && [[ "$(git rev-parse --git-dir)" == .git ]] ) >/dev/null 2>&1; then
    ```

* make sure that Bazel works again
    ```bash
    [arch@archlinux bazel-watcher]$ ls -a /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing
    .  ..
    [arch@archlinux bazel-watcher]$ bazel --batch build :all
    INFO: $TEST_TMPDIR defined: output root default is '/tmp/.cache/bazel' and max_idle_secs default is '15'.
    Error: corrupt installation: file '/tmp/.cache/bazel/_bazel_arch/install/f20169627a8110e2cc3d005319e97c94/_embedded_binaries/embedded_tools/tools/build_defs/repo/git.bzl' modified.  Please remove '/tmp/.cache/bazel/_bazel_arch/install/f20169627a8110e2cc3d005319e97c94' and try again.
    [arch@archlinux bazel-watcher]$ touch -m -t 202712120101 /tmp/.cache/bazel/_bazel_arch/install/f20169627a8110e2cc3d005319e97c94/_embedded_binaries/embedded_tools/tools/build_defs/repo/git.bzl
    [arch@archlinux bazel-watcher]$ bazel --batch build :all
    INFO: $TEST_TMPDIR defined: output root default is '/tmp/.cache/bazel' and max_idle_secs default is '15'.
    WARNING: /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing/WORKSPACE:1: Workspace name in /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing/WORKSPACE (@build_bazel_integration_testing) does not match the name given in the repository's definition (@com_github_bazelbuild_bazel_integration_testing); this will cause a build error in future versions
    INFO: Analysed target //:go_prefix (6 packages loaded).
    INFO: Found 1 target...
    Target //:go_prefix up-to-date (nothing to build)
    INFO: Elapsed time: 13.318s, Critical Path: 0.07s
    INFO: Build completed successfully, 1 total action
    [arch@archlinux bazel-watcher]$ ls -a /tmp/.cache/bazel/_bazel_arch/f2207b308c89ea5d32323052637210b1/external/com_github_bazelbuild_bazel_integration_testing
    .  ..  AUTHORS  bazel_integration_test  bazel_integration_test.bzl  bazel_version.bzl  BUILD  .ci  CODEOWNERS  CONTRIBUTING.md  .git  .gitignore  go  java  javatests  LICENSE  README.md  tools  WORKSPACE
    ```

Closes #4358.

PiperOrigin-RevId: 181151078

1 files changed, 1 insertions, 1 deletions

diff --git a/tools/build_defs/repo/git.bzl b/tools/build_defs/repo/git.bzl
index 514795108f..3e708df791 100644
--- a/tools/build_defs/repo/git.bzl
+++ b/tools/build_defs/repo/git.bzl
@@ -27,7 +27,7 @@ def _clone_or_update(ctx):
   st = ctx.execute(['bash', '-c', """
 set -ex
 ( cd {working_dir} &&
-    if ! ( cd '{dir}' && git rev-parse --git-dir ) >/dev/null 2>&1; then
+    if ! ( cd '{dir}' && [[ "$(git rev-parse --git-dir)" == '.git' ]] ) >/dev/null 2>&1; then
       rm -rf '{dir}'
       git clone '{remote}' '{dir}'
     fi