## Add support for Windows linkstatic computed default

This uses the same technique as `cc_binary` with/without aspects.
Essentially we are declaring two rules named cc_test with different private attribute defaults. This is primarily done this way to hide the implementation details of computed defaults until something like
[bazel/issues/14434](#14434) is implemented.

NOTE: When `cc_test` written in Starlark is made the default, this _will_ introduce a behavior change -- notably that we will default linkstatic based on whether we are _targeting_ Windows, not whether the host Platform is Windows (as is done today).
The latter heuristic may have been the best available option before Platforms, but it does not match the actual intent.
PiperOrigin-RevId: 441472088

src/main/starlark/builtins_bzl/common/cc/cc_binary.bzl

@@ -582,9 +582,16 @@ def _malloc_for_target(ctx, cpp_config):
     return ctx.attr.malloc
 
 def _get_link_staticness(ctx, cpp_config):
+    linkstatic_attr = None
+    if hasattr(ctx.attr, "_linkstatic_explicitly_set") and not ctx.attr._linkstatic_explicitly_set:
+        # If we know that linkstatic is not explicitly set, use computed default:
+        linkstatic_attr = semantics.get_linkstatic_default(ctx)
+    else:
+        linkstatic_attr = ctx.attr.linkstatic
+
     if cpp_config.dynamic_mode() == "FULLY":
         return _LINKING_DYNAMIC
-    elif cpp_config.dynamic_mode() == "OFF" or ctx.attr.linkstatic:
+    elif cpp_config.dynamic_mode() == "OFF" or linkstatic_attr:
         return _LINKING_STATIC
     else:
         return _LINKING_DYNAMIC

src/main/starlark/builtins_bzl/common/cc/cc_test.bzl

@@ -40,6 +40,11 @@ _cc_test_attrs.update(
             "@" + paths.join(semantics.get_platforms_root(), "os:watchos"),
         ],
     ),
+    _windows_constraints = attr.label_list(
+        default = [
+            "@" + paths.join(semantics.get_platforms_root(), "os:windows"),
+        ],
+    ),
     stamp = attr.int(values = [-1, 0, 1], default = 0),
     linkstatic = attr.bool(default = False),
     malloc = attr.label(

src/main/starlark/builtins_bzl/common/cc/semantics.bzl

@@ -14,6 +14,8 @@
 
 """Semantics for Bazel cc rules"""
 
+load(":common/cc/cc_helper.bzl", "cc_helper")
+
 cc_common = _builtins.toplevel.cc_common
 
 def _should_create_empty_archive():
@@ -78,6 +80,17 @@ def _check_experimental_cc_shared_library(ctx):
     if not cc_common.check_experimental_cc_shared_library():
         fail("Pass --experimental_cc_shared_library to use cc_shared_library")
 
+def _get_linkstatic_default(ctx):
+    if ctx.attr._is_test:
+        # By default Tests do not link statically. Except on Windows.
+        if cc_helper.has_target_constraints(ctx, ctx.attr._windows_constraints):
+            return True
+        else:
+            return False
+    else:
+        # Binaries link statically.
+        return True
+
 semantics = struct(
     ALLOWED_RULES_IN_DEPS = [
         "cc_library",
@@ -108,4 +121,5 @@ semantics = struct(
     get_interface_deps_allowed_attr = _get_interface_deps_allowed_attr,
     should_use_interface_deps_behavior = _should_use_interface_deps_behavior,
     check_experimental_cc_shared_library = _check_experimental_cc_shared_library,
+    get_linkstatic_default = _get_linkstatic_default,
 )