fix: windows typecheck_test .sh vs .bat error (#732)

ts/private/build_test.bzl

@@ -11,12 +11,15 @@ It is used to force Bazel to build some of its dependencies, in the case where
 """
 
 def _build_test_impl(ctx):
-    executable = ctx.actions.declare_file(ctx.label.name + ".sh")
+    # See https://github.com/bazelbuild/bazel-skylib/blob/1.7.1/rules/build_test.bzl#L19-L33
 
+    extension = ".bat" if ctx.attr.is_windows else ".sh"
+    content = "exit 0" if ctx.attr.is_windows else "#!/usr/bin/env bash\nexit 0"
+    executable = ctx.actions.declare_file(ctx.label.name + extension)
     ctx.actions.write(
         output = executable,
         is_executable = True,
-        content = "#!/usr/bin/env bash\nexit 0",
+        content = content,
     )
 
     return DefaultInfo(
@@ -26,11 +29,22 @@ def _build_test_impl(ctx):
         runfiles = ctx.runfiles(files = ctx.files.targets),
     )
 
-build_test = rule(
+_build_test = rule(
     doc = _DOC,
     implementation = _build_test_impl,
     attrs = {
         "targets": attr.label_list(allow_files = True),
+        "is_windows": attr.bool(mandatory = True),
     },
     test = True,
 )
+
+def build_test(name, **kwargs):
+    _build_test(
+        name = name,
+        is_windows = select({
+            "@bazel_tools//src/conditions:host_windows": True,
+            "//conditions:default": False,
+        }),
+        **kwargs
+    )