Avoid depending on the value of the --stamp flag if possible (#1035)

* Stamp detect
* Stamp detect tar.bzl
* Stamp detect zip.bzl

Author: justinhorvitz

pkg/private/tar/tar.bzl

@@ -24,7 +24,7 @@ load(
     "create_mapping_context_from_ctx",
     "write_manifest",
 )
-load("//pkg/private:util.bzl", "setup_output_files", "substitute_package_variables")
+load("//pkg/private:util.bzl", "get_stamp_detect", "setup_output_files", "substitute_package_variables")
 
 # TODO(aiuto): Figure  out how to get this from the python toolchain.
 # See check for lzma in archive.py for a hint at a method.
@@ -38,7 +38,6 @@ SUPPORTED_TAR_COMPRESSIONS = (
     ["", "gz", "bz2", "xz"] if HAS_XZ_SUPPORT else ["", "gz", "bz2"]
 )
 _DEFAULT_MTIME = -1
-_stamp_condition = Label("//pkg/private:private_stamp_detect")
 
 def _remap(remap_paths, path):
     """If path starts with a key in remap_paths, rewrite it."""
@@ -362,9 +361,6 @@ def pkg_tar(name, **kwargs):
     pkg_tar_impl(
         name = name,
         out = kwargs.pop("out", None) or (name + "." + extension),
-        private_stamp_detect = select({
-            _stamp_condition: True,
-            "//conditions:default": False,
-        }),
+        private_stamp_detect = get_stamp_detect(kwargs.get("stamp", 0)),
         **kwargs
     )

pkg/private/util.bzl

@@ -15,6 +15,8 @@
 
 load("//pkg:providers.bzl", "PackageVariablesInfo")
 
+_stamp_condition = Label("//pkg/private:private_stamp_detect")
+
 def setup_output_files(ctx, package_file_name = None, default_output_file = None):
     """Provide output file metadata for common packaging rules
 
@@ -126,3 +128,21 @@ def get_repo_mapping_manifest(src):
         # https://github.com/bazelbuild/bazel/issues/19937
         return getattr(files_to_run_provider, "repo_mapping_manifest")
     return None
+
+def get_stamp_detect(stamp_attr):
+    """Returns a boolean or select to resolve the stamp setting.
+
+    Args:
+      stamp_attr: Rule-level stamp attribute value.
+
+    Returns:
+      Boolean or select to resolve the stamp setting.
+    """
+    if stamp_attr == 1:
+        return True
+    if stamp_attr == -1:
+        return select({
+            _stamp_condition: True,
+            "//conditions:default": False,
+        })
+    return False

pkg/private/zip/zip.bzl

@@ -25,12 +25,11 @@ load(
 )
 load(
     "//pkg/private:util.bzl",
+    "get_stamp_detect",
     "setup_output_files",
     "substitute_package_variables",
 )
 
-_stamp_condition = Label("//pkg/private:private_stamp_detect")
-
 def _pkg_zip_impl(ctx):
     outputs, output_file, _ = setup_output_files(ctx)
 
@@ -186,9 +185,6 @@ def pkg_zip(name, out = None, **kwargs):
     pkg_zip_impl(
         name = name,
         out = out,
-        private_stamp_detect = select({
-            _stamp_condition: True,
-            "//conditions:default": False,
-        }),
+        private_stamp_detect = get_stamp_detect(kwargs.get("stamp", 0)),
         **kwargs
     )