Force clean+fetch when re-running configure with different settings. (#4285)

* Run bazel clean and bazel fetch in the configure script even when building
  without GPU support to force clean+fetch if the user re-runs ./configure
  with a different setting.
* Print a more actionable error messsage if the user attempts to build with
  --config=cuda but did not configure TensorFlow to build with GPU support.
* Update the BUILD file in @local_config_cuda to use repository-local labels.

Fixes #4105

configure

@@ -5,6 +5,11 @@ pushd `dirname $0` #> /dev/null
 SOURCE_BASE_DIR=`pwd -P`
 popd > /dev/null
 
+function bazel_clean_and_fetch() {
+  bazel clean --expunge
+  bazel fetch //tensorflow/...
+}
+
 ## Set up python-related environment settings
 while true; do
   fromuser=""
@@ -114,6 +119,7 @@ done
 export TF_NEED_CUDA
 if [ "$TF_NEED_CUDA" == "0" ]; then
   echo "Configuration finished"
+  bazel_clean_and_fetch
   exit
 fi
 
@@ -300,7 +306,6 @@ EOF
   TF_CUDA_COMPUTE_CAPABILITIES=""
 done
 
-bazel clean --expunge
-bazel fetch //...
+bazel_clean_and_fetch
 
 echo "Configuration finished"

third_party/gpus/crosstool/BUILD.tpl

@@ -2,10 +2,12 @@ licenses(["restricted"])
 
 package(default_visibility = ["//visibility:public"])
 
-filegroup(
-    name = "crosstool",
-    srcs = ["CROSSTOOL"],
-    output_licenses = ["unencumbered"],
+cc_toolchain_suite(
+    name = "toolchain",
+    toolchains = {
+        "local|compiler": ":cc-compiler-local",
+        "darwin|compiler": ":cc-compiler-darwin",
+    },
 )
 
 cc_toolchain(

third_party/gpus/cuda_configure.bzl

@@ -331,6 +331,33 @@ def _file(repository_ctx, label):
       {})
 
 
+_DUMMY_CROSSTOOL_BZL_FILE = """
+def error_gpu_disabled():
+  fail("ERROR: Building with --config=cuda but TensorFlow is not configured " +
+       "to build with GPU support. Please re-run ./configure and enter 'Y' " +
+       "at the prompt to build with GPU support.")
+
+  native.genrule(
+      name = "error_gen_crosstool",
+      outs = ["CROSSTOOL"],
+      cmd = "echo 'Should not be run.' && exit 1",
+  )
+
+  native.filegroup(
+      name = "crosstool",
+      srcs = [":CROSSTOOL"],
+      output_licenses = ["unencumbered"],
+  )
+"""
+
+
+_DUMMY_CROSSTOOL_BUILD_FILE = """
+load("//crosstool:error_gpu_disabled.bzl", "error_gpu_disabled")
+
+error_gpu_disabled()
+"""
+
+
 def _create_dummy_repository(repository_ctx):
   cpu_value = _cpu_value(repository_ctx)
   symlink_files = _cuda_symlink_files(cpu_value, _DEFAULT_CUDA_VERSION,
@@ -371,6 +398,12 @@ def _create_dummy_repository(repository_ctx):
                for c in _DEFAULT_CUDA_COMPUTE_CAPABILITIES]),
        })
 
+  # If cuda_configure is not configured to build with GPU support, and the user
+  # attempts to build with --config=cuda, add a dummy build rule to intercept
+  # this and fail with an actionable error message.
+  repository_ctx.file("crosstool/error_gpu_disabled.bzl",
+                      _DUMMY_CROSSTOOL_BZL_FILE)
+  repository_ctx.file("crosstool/BUILD", _DUMMY_CROSSTOOL_BUILD_FILE)
 
 def _symlink_dir(repository_ctx, src_dir, dest_dir):
   """Symlinks all the files in a directory.

tools/bazel.rc.template

@@ -1,4 +1,4 @@
-build:cuda --crosstool_top=@local_config_cuda//crosstool
+build:cuda --crosstool_top=@local_config_cuda//crosstool:toolchain
 build:cuda --define=using_cuda=true --define=using_cuda_nvcc=true
 
 build --force_python=py$PYTHON_MAJOR_VERSION