[libc++][test] Adds backdeployment shorthands. (#78204)

Some changes in libc++ affect the dylib. These changes are not present
on systems that use the system dylib. Currently that are the Apple
backdeployment targets. Figuring out which MacOS versions to target is
not trivial for non-Apple engineers. These shorthands make it easier to
select the proper feature make a test UNSUPPORTED or XFAIL.

During the design discussion with Louis we considered whether or not to
add preprocessor definitions to allow partial disabling of a test. This
would be useful when an existing feature is changed by modifying the
dylib. In the end we decided not to add this feature to avoid additional
complexity in the tests. Instead the test will be disabled for that
target.

Author: mordante

libcxx/utils/libcxx/test/features.py

@@ -526,36 +526,118 @@ def check_gdb(cfg):
 # target that doesn't support it will fail at compile time, not at runtime. This can
 # be achieved by creating a `.verify.cpp` test that checks for the right errors, and
 # mark that test as requiring `stdlib=<vendor>-libc++ && target=<target>`.
+#
+# Since it is not always known which deployment target to pick there are
+# short-hands based on the LLVM version like using-built-library-before-llvm-xx.
+# These short-hands make it easy for libc++ developers to select the proper
+# version the feature will be available in and allows vendors to set the proper
+# target information.
 DEFAULT_FEATURES += [
+    # Backdeployment short-hands
+    Feature(
+        name="using-built-library-before-llvm-11",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "stdlib=apple-libc++ && target={{.+}}-apple-macosx{{(10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0)(.0)?}}",
+            cfg.available_features,
+        ),
+    ),
+    Feature(
+        name="using-built-library-before-llvm-12",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-11 || (stdlib=apple-libc++ && target={{.+}}-apple-macosx12.{{(0|1|2)}}.0)",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-13",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-12 || (stdlib=apple-libc++ && target={{.+}}-apple-macosx{{((12.(3|4|5|6|7))|(13.(0|1|2|3)))}}.0)",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-14",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-13",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-15",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-14 || (stdlib=apple-libc++ && target={{.+}}-apple-macosx13.{{(4|5|6)}}.0)",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-16",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-15 || (stdlib=apple-libc++ && target={{.+}}-apple-macosx14.{{(0|1|2|3)}}.0)",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-17",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-16",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-18",
+        when=lambda cfg: BooleanExpression.evaluate(
+            # For now, no released version of macOS contains LLVM 18
+            # TODO(ldionne) Please provide the correct value.
+            "using-built-library-before-llvm-17 || stdlib=apple-libc++ && target={{.+}}-apple-macosx{{.+}}",
+            cfg.available_features,
+        ),
+    ),
+
+    Feature(
+        name="using-built-library-before-llvm-19",
+        when=lambda cfg: BooleanExpression.evaluate(
+            # For now, no released version of macOS contains LLVM 19
+            # TODO(ldionne) Please provide the correct value.
+            "using-built-library-before-llvm-18 || stdlib=apple-libc++ && target={{.+}}-apple-macosx{{.+}}",
+            cfg.available_features,
+        ),
+    ),
+
     # Tests that require std::to_chars(floating-point) in the built library
     Feature(
         name="availability-fp_to_chars-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "stdlib=apple-libc++ && target={{.+}}-apple-macosx{{(10.13|10.14|10.15|11.0|12.0|13.0)(.0)?}}",
+            "using-built-library-before-llvm-13",
             cfg.available_features,
         ),
     ),
     # Tests that require https://wg21.link/P0482 support in the built library
     Feature(
         name="availability-char8_t_support-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "stdlib=apple-libc++ && target={{.+}}-apple-macosx{{(10.13|10.14|10.15|11.0)(.0)?}}",
+            "using-built-library-before-llvm-11",
             cfg.available_features,
         ),
     ),
     # Tests that require __libcpp_verbose_abort support in the built library
     Feature(
         name="availability-verbose_abort-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "stdlib=apple-libc++ && target={{.+}}-apple-macosx{{(10.13|10.14|10.15|11.0|12.0|13.0)(.0)?}}",
+            "using-built-library-before-llvm-13",
             cfg.available_features,
         ),
     ),
     # Tests that require std::pmr support in the built library
     Feature(
         name="availability-pmr-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "stdlib=apple-libc++ && target={{.+}}-apple-macosx{{(10.13|10.14|10.15|11.0|12.0|13.0)(.0)?}}",
+            "using-built-library-before-llvm-13",
             cfg.available_features,
         ),
     ),
@@ -579,8 +661,15 @@ def check_gdb(cfg):
     Feature(
         name="availability-tzdb-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            # TODO(ldionne) Please provide the correct value.
-            "(stdlib=apple-libc++ && target={{.+}}-apple-macosx{{(10.13|10.14|10.15|11.0|12.0|13.0)(.0)?}})",
+            "using-built-library-before-llvm-19",
+            cfg.available_features,
+        ),
+    ),
+    # Tests that require support for <print> and std::print in <ostream> in the built library.
+    Feature(
+        name="availability-print-missing",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "using-built-library-before-llvm-18",
             cfg.available_features,
         ),
     ),