Make cc_configure on Windows more robust

1. Throw an error if Bash-on-Windows is found instead of MSYS bash
2. Introduce BAZEL_VS environment variable
3. Output more information

Fix bazelbuild#1847

--
Change-Id: Ic4571c6c792d9b81df4cd800b8f19d121cc44c33
Reviewed-on: https://bazel-review.googlesource.com/#/c/6330
MOS_MIGRATED_REVID=134531295

site/versions/master/docs/windows.md

@@ -48,6 +48,9 @@ To build C++ targets, you will need:
 <br/>We are using MSVC as the native C++ toolchain, so please ensure you have Visual
 Studio installed with the Visual C++ components
 (which is NOT the default installation type of Visual Studio).
+You can set BAZEL\_VS environment variable to tell Bazel
+where Visual Studio is, otherwise Bazel will try to find the latest version installed.
+<br/>For example: `export BAZEL_VS="C:/Program Files (x86)/Microsoft Visual Studio 14.0"`
 
 * [Python 2.7](https://www.python.org/downloads/)
 <br/>Currently, we use python wrapper scripts to call the actual MSVC compiler, so

src/main/native/build_windows_jni.sh

@@ -29,12 +29,15 @@ trap "rm -fr \"$VSTEMP\"" EXIT
 
 # Find Visual Studio. We don't have any regular environment variables available
 # so this is the best we can do.
-VSVERSION="$(ls "C:/Program Files (x86)" | grep -E "Microsoft Visual Studio [0-9]+" | sort | tail -n 1)"
-if [[ "$VSVERSION" == "" ]]; then
-  echo "Visual Studio not found"
-  exit 1
+if [ -z "${BAZEL_VS+set}" ]; then
+  VSVERSION="$(ls "C:/Program Files (x86)" | grep -E "Microsoft Visual Studio [0-9]+" | sort --version-sort | tail -n 1)"
+  if [[ "$VSVERSION" == "" ]]; then
+    echo "Visual Studio not found"
+    exit 1
+  fi
+  BAZEL_VS="C:/Program Files (x86)/$VSVERSION"
 fi
-VSVARS="C:/Program Files (x86)/$VSVERSION/VC/VCVARSALL.BAT"
+VSVARS="${BAZEL_VS}/VC/VCVARSALL.BAT"
 
 # Find Java. $(JAVA) in the BUILD file points to external/local_jdk/..., which
 # is not very useful for anything not MSYS-based.

tools/cpp/cc_configure.bzl

@@ -374,7 +374,8 @@ def _find_python(repository_ctx):
   if "BAZEL_PYTHON" in repository_ctx.os.environ:
     return repository_ctx.os.environ["BAZEL_PYTHON"]
   auto_configure_warning("'BAZEL_PYTHON' is not set, start looking for python in PATH.")
-  python_binary = _which_cmd(repository_ctx, "python.exe", "C:\\Python27\\python.exe")
+  python_binary = _which_cmd(repository_ctx, "python.exe")
+  auto_configure_warning("Python found at %s" % python_binary)
   return python_binary
 
 def _find_bash(repository_ctx):
@@ -383,14 +384,27 @@ def _find_bash(repository_ctx):
     return repository_ctx.os.environ["BAZEL_SH"]
   auto_configure_warning("'BAZEL_SH' is not set, start looking for bash in PATH.")
   bash_binary = _which_cmd(repository_ctx, "bash.exe")
+  auto_configure_warning("Bash binary found at %s" % bash_binary)
+  if bash_binary.lower() == "c:/windows/system32/bash.exe":
+    auto_configure_fail("Bash on Windows currently doesn't work with Bazel, please set BAZEL_SH or make sure 'which bash' returns MSYS bash binary.")
   return bash_binary
 
 def _find_vs_path(repository_ctx):
   """Find Visual Studio install path."""
+  if "BAZEL_VS" in repository_ctx.os.environ:
+    return repository_ctx.os.environ["BAZEL_VS"]
+  auto_configure_warning("'BAZEL_VS' is not set, start looking for the latest Visual Studio installed.")
   bash_bin = _find_bash(repository_ctx)
   program_files_dir = _get_env_var(repository_ctx, "ProgramFiles(x86)", "C:\\Program Files (x86)")
-  vs_version = _execute(repository_ctx, [bash_bin, "-c", "ls '%s' | grep -E 'Microsoft Visual Studio [0-9]+' | sort | tail -n 1" % program_files_dir])
-  return program_files_dir + "/" + vs_version
+  # --version-sort let us find the latest version of Visual Studio
+  # Make sure we are using msys sort, the Windows one doesn't support --version-sort.
+  sort_binary = bash_bin[0:-8].replace("\\", "/") + "sort.exe"
+  vs_version = _execute(repository_ctx, [bash_bin, "-c", "ls '%s' | grep -E 'Microsoft Visual Studio [0-9]+' | %s --version-sort | tail -n 1" % (program_files_dir, sort_binary)])
+  if not vs_version:
+    auto_configure_fail("Visual Studio not found under %s" % program_files_dir)
+  vs_dir = program_files_dir + "/" + vs_version
+  auto_configure_warning("Visual Studio found at %s" % vs_dir)
+  return vs_dir
 
 
 def _find_env_vars(repository_ctx, vs_path):