Let shellzelisk fallback to bazel-real if it's the requested version.

This means that if you "apt-get install bazel" and that happens to be version "2.0.0" and in your `.bazelversion` file you have "2.0.0", then the new Bazel wrapper will just use the Bazel binary installed as the "latest" Bazel by "apt-get install bazel" and not ask the user to install the same version of Bazel as a side-by-side binary using "apt-get install bazel-2.0.0".

The same applies when using the Bazel installer or any other setup that uses the wrapper script.

Closes #10356.

RELNOTES: None.
PiperOrigin-RevId: 285941301

scripts/packages/bazel.sh

@@ -139,10 +139,23 @@ if [[ -z $bazel_version ]]; then
 fi
 
 BAZEL_REAL="${wrapper_dir}/bazel-${bazel_version}-${os_arch_suffix}"
+
+# Try without the architecture suffix.
 if [[ ! -x ${BAZEL_REAL} ]]; then
   BAZEL_REAL="${wrapper_dir}/bazel-${bazel_version}"
 fi
 
+# Last try: Maybe `bazel-real` is actually the requested correct version?
+readonly bazel_real_path="${wrapper_dir}/bazel-real"
+if [[ ! -x ${BAZEL_REAL} && -x ${bazel_real_path} ]]; then
+  # Note that "bazel --version" is very fast and doesn't start the Bazel server,
+  # as opposed to "bazel version".
+  readonly bazel_real_version="$("${bazel_real_path}" --version | grep '^bazel ' | cut -d' ' -f2)"
+  if [[ $bazel_real_version == $bazel_version ]]; then
+    BAZEL_REAL="${bazel_real_path}"
+  fi
+fi
+
 if [[ ! -x $BAZEL_REAL ]]; then
   color "31" "ERROR: The project you're trying to build requires Bazel ${bazel_version} (${reason}), but it wasn't found in ${wrapper_dir}."
 

src/test/shell/bazel/bazel_wrapper_test.sh

@@ -45,13 +45,19 @@ set -e
 wrapper=$(rlocation io_bazel/scripts/packages/bazel.sh)
 
 mock_bazel() {
-  cat > "$1" <<'EOF'
+  {
+    cat <<'EOF'
 #!/bin/bash
 set -euo pipefail
-echo "Hello from $(basename $0)!"
-echo "My args: $@"
+if [[ ${1:-""} == "--version" ]]; then
+  echo "bazel BAZEL_VERSION"
+else
+  echo "Hello from $(basename $0)!"
+  echo "My args: $@"
+fi
 exit 0
 EOF
+  } | sed "s/BAZEL_VERSION/$2/" > "$1"
   chmod +x "$1"
 }
 
@@ -65,9 +71,9 @@ setup_mock() {
   mkdir bin
   cp "$wrapper" "bin/bazel"
   chmod +x "bin/bazel"
-  mock_bazel "bin/bazel-0.29.1"
-  mock_bazel "bin/bazel-1.0.1"
-  mock_bazel "bin/bazel-real"
+  mock_bazel "bin/bazel-0.29.1" "0.29.1"
+  mock_bazel "bin/bazel-1.0.1" "1.0.1"
+  mock_bazel "bin/bazel-real" "1.1.0"
 
   # We don't want USE_BAZEL_VERSION passed by --test_env to affect this test.
   unset USE_BAZEL_VERSION
@@ -77,9 +83,9 @@ setup_mock() {
 test_use_bazel_version_envvar() {
   setup_mock
 
-  USE_BAZEL_VERSION="0.29.1" ../bin/bazel version &> "$TEST_log"
+  USE_BAZEL_VERSION="0.29.1" ../bin/bazel build &> "$TEST_log"
   expect_log "Hello from bazel-0.29.1"
-  expect_log "My args: version"
+  expect_log "My args: build"
 }
 
 test_bazelversion_file() {
@@ -206,4 +212,13 @@ EOF
   expect_log "My args: build //src:bazel"
 }
 
+test_wrapper_detects_version_of_bazel_real() {
+  setup_mock
+
+  echo "1.1.0" > .bazelversion
+  ../bin/bazel &> "$TEST_log"
+  expect_log "Hello from bazel-real"
+  expect_log "My args:"
+}
+
 run_suite "Integration tests for scripts/packages/bazel.sh."