Set default python3_path to python.exe on Windows

When building py_binary for host with --host_force_python=py3,
--python3_path is not taken, instead python3.exe is always used.
It doesn't work because python3.exe usually doesn't exist on
Windows. So here we set the default to python.exe

Fixed https://github.com/bazelbuild/bazel/issues/2752

Change-Id: Ie48156d93ae1f28338947ea121ab2071e1b820e1
PiperOrigin-RevId: 152130801

1 files changed, 26 insertions, 4 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java
index d1768e1611..6c1a124d88 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java
@@ -23,8 +23,9 @@ import com.google.devtools.build.lib.analysis.config.ConfigurationFragmentFactor
 import com.google.devtools.build.lib.analysis.config.FragmentOptions;
 import com.google.devtools.build.lib.analysis.config.InvalidConfigurationException;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.util.OS;
+import com.google.devtools.common.options.Converter;
 import com.google.devtools.common.options.Option;
-
 import javax.annotation.Nullable;
 
 /**
@@ -34,6 +35,24 @@ import javax.annotation.Nullable;
 public class BazelPythonConfiguration extends BuildConfiguration.Fragment {
 
   /**
+  * A path converter for python3 path
+  */
+  public static class Python3PathConverter implements Converter<String> {
+    @Override
+    public String convert(String input) {
+      if (input.equals("auto")) {
+        return OS.getCurrent() == OS.WINDOWS ? "python" : "python3";
+      }
+      return input;
+    }
+
+    @Override
+    public String getTypeDescription() {
+      return "An option for python3 path";
+    }
+  }
+
+  /**
    * Bazel-specific Python configuration options.
    */
   public static final class Options extends FragmentOptions {
@@ -43,10 +62,13 @@ public class BazelPythonConfiguration extends BuildConfiguration.Fragment {
       help = "Local path to the Python2 executable.")
     public String python2Path;
 
-    @Option(name = "python3_path",
-      defaultValue = "python3",
+    @Option(
+      name = "python3_path",
+      converter = Python3PathConverter.class,
+      defaultValue = "auto",
       category = "version",
-      help = "Local path to the Python3 executable.")
+      help = "Local path to the Python3 executable."
+    )
     public String python3Path;
 
     @Option(name = "experimental_python_import_all_repositories",