Fix problems with the non-strict Python toolchain

1. Change the Python workspace suffix from registering all toolchains (via `:all`) in the @bazel_tools//tools/python package, to just registering the normal autodetecting toolchain. This ensures that the non-strict toolchain never inadvertently gets higher precedence than the standard toolchain. (This may have been working before by chance, but let's be safe and not rely on target pattern expansion order.) A side-effect of this is that we need to make our analysis and shell integration tests use the standard toolchain's name.

2. Fix bad quoting that caused the suggested command line flag to not be printed

3. Now that the wrapper is shared, there's two possible names for the toolchain, so output the right one in error messages.

Fixes bazelbuild#8576, follow-up to bazelbuild#8547.

RELNOTES: None
PiperOrigin-RevId: 251937305

src/main/java/com/google/devtools/build/lib/bazel/rules/python/python.WORKSPACE

@@ -1 +1,7 @@
-register_toolchains("@bazel_tools//tools/python:all")
+# Don't use the target pattern :all, because we don't want to register
+# :autodetecting_toolchain_nonstrict. That toolchain opts out of Python version
+# checking, so the user should have to explicitly declare it on their command
+# line or WORKSPACE file. (And even if we did register it here, we still
+# couldn't use :all because we'd want to ensure it has the lowest possible
+# priority.)
+register_toolchains("@bazel_tools//tools/python:autodetecting_toolchain")

src/test/java/com/google/devtools/build/lib/analysis/mock/BazelAnalysisMock.java

@@ -78,7 +78,7 @@ public List<String> getWorkspaceContents(MockToolsConfig config) {
             "bind(name = 'android/sdk', actual='@bazel_tools//tools/android:sdk')",
             "register_toolchains('@bazel_tools//tools/cpp:all')",
             "register_toolchains('@bazel_tools//tools/jdk:all')",
-            "register_toolchains('@bazel_tools//tools/python:all')",
+            "register_toolchains('@bazel_tools//tools/python:autodetecting_toolchain')",
             "local_repository(name = 'local_config_platform', path = '"
                 + localConfigPlatformWorkspace
                 + "')"));

src/test/java/com/google/devtools/build/lib/packages/util/BazelMockPythonSupport.java

@@ -70,7 +70,8 @@ public void setup(MockToolsConfig config) throws IOException {
         "    py3_runtime = ':py3_interpreter',",
         ")",
         "toolchain(",
-        "    name = 'default_python_toolchain',",
+        "    # The Python workspace suffix looks to register a toolchain of this name.",
+        "    name = 'autodetecting_toolchain',",
         "    toolchain = ':default_py_runtime_pair',",
         "    toolchain_type = ':toolchain_type',",
         ")",

tools/python/pywrapper_template.txt

@@ -5,14 +5,22 @@
 # https://groups.google.com/forum/?nomobile=true#!topic/bazel-dev/4Ql_7eDcLC0
 # We do lose the ability to set -o pipefail.
 
-FAILURE_HEADER="\
+STRICT=%STRICT%
+
+if [ "$STRICT" = "1" ]; then
+  FAILURE_HEADER="\
 Error occurred while attempting to use the default Python toolchain \
 (@bazel_tools//tools/python:autodetecting_toolchain)."
+else
+  FAILURE_HEADER="\
+Error occurred while attempting to use the non-strict autodetecting Python \
+toolchain (@bazel_tools//tools/python:autodetecting_toolchain_nonstrict)."
+fi
 
 die() {
-    echo "$FAILURE_HEADER" 1>&2
-    echo "$1" 1>&2
-    exit 1
+  echo "$FAILURE_HEADER" 1>&2
+  echo "$1" 1>&2
+  exit 1
 }
 
 # We use `which` to locate the Python interpreter command on PATH. `command -v`
@@ -38,11 +46,11 @@ die() {
 PYTHON_BIN=`PATH="$PATH" which python%VERSION% || echo ""`
 USED_FALLBACK=0
 if [ -z "${PYTHON_BIN:-}" ]; then
-    PYTHON_BIN=`PATH="$PATH" which python || echo ""`
-    USED_FALLBACK=1
+  PYTHON_BIN=`PATH="$PATH" which python || echo ""`
+  USED_FALLBACK=1
 fi
 if [ -z "${PYTHON_BIN:-}" ]; then
-    die "Neither 'python%VERSION%' nor 'python' were found on the target \
+  die "Neither 'python%VERSION%' nor 'python' were found on the target \
 platform's PATH, which is:
 
 $PATH
@@ -53,7 +61,6 @@ documentation for py_runtime_pair \
 (https://github.com/bazelbuild/bazel/blob/master/tools/python/toolchain.bzl)."
 fi
 
-STRICT=%STRICT%
 if [ "$STRICT" = "1" ]; then
   # Verify that we grabbed an interpreter with the right version.
   VERSION_STR=`"$PYTHON_BIN" -V 2>&1` \
@@ -75,7 +82,7 @@ your build worked prior to Bazel 0.27, and you're sure your targets do not \
 require Python %VERSION%, you can opt out of this version check by using the \
 non-strict autodetecting toolchain instead of the standard autodetecting \
 toolchain. This can be done by passing the flag \
-`--extra_toolchains=@bazel_tools//tools/python:autodetecting_toolchain_nonstrict` \
+\`--extra_toolchains=@bazel_tools//tools/python:autodetecting_toolchain_nonstrict\` \
 on the command line or adding it to your bazelrc."
   fi
 fi