[libc++] Adds a new feature-test macro generator class. (llvm#90889)

The new feature-test macro generator uses a JSON file as input.
Separating the
code from the data allows for testing the code. The generator has
several tests.

This JSON format is based on the new format proposed in llvm#88630

At the moment the FTM script has the existing code and an unused new
generator. Followup patches will complete the generator and convert the
existing
Python `dict` to the new JSON format. Since that conversion is a manual
job and
quite a bit of work the transition path has some unused code for some
time.

libcxx/test/libcxx/feature_test_macro/implemented_ftms.sh.py

@@ -0,0 +1,54 @@
+# ===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# ===----------------------------------------------------------------------===##
+
+# RUN: %{python} %s %{libcxx-dir}/utils %{libcxx-dir}/test/libcxx/feature_test_macro/test_data.json
+
+import sys
+
+sys.path.append(sys.argv[1])
+from generate_feature_test_macro_components import FeatureTestMacros
+
+
+def test(output, expected):
+    assert output == expected, f"expected\n{expected}\n\noutput\n{output}"
+
+
+ftm = FeatureTestMacros(sys.argv[2])
+test(
+    ftm.implemented_ftms,
+    {
+        "__cpp_lib_any": {
+            "c++17": "201606L",
+            "c++20": "201606L",
+            "c++23": "201606L",
+            "c++26": "201606L",
+        },
+        "__cpp_lib_barrier": {
+            "c++20": "201907L",
+            "c++23": "201907L",
+            "c++26": "201907L",
+        },
+        "__cpp_lib_format": {
+            "c++20": None,
+            "c++23": None,
+            "c++26": None,
+        },
+        "__cpp_lib_parallel_algorithm": {
+            "c++17": "201603L",
+            "c++20": "201603L",
+            "c++23": "201603L",
+            "c++26": "201603L",
+        },
+        "__cpp_lib_variant": {
+            "c++17": "202102L",
+            "c++20": "202102L",
+            "c++23": "202102L",
+            "c++26": "202102L",
+        },
+    },
+)

libcxx/test/libcxx/feature_test_macro/invalid.sh.py

@@ -0,0 +1,108 @@
+# ===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# ===----------------------------------------------------------------------===##
+
+# RUN: %{python} %s %{libcxx-dir}/utils %t
+
+import sys
+import json
+
+sys.path.append(sys.argv[1])
+from generate_feature_test_macro_components import FeatureTestMacros
+
+
+def test(output, expected):
+    assert output == expected, f"expected\n{expected}\n\noutput\n{output}"
+
+
+def test_error(data, type, message):
+    tmp = sys.argv[2]
+    with open(tmp, "w") as file:
+        file.write(json.dumps(data))
+    ftm = FeatureTestMacros(tmp)
+    try:
+        ftm.implemented_ftms
+    except type as error:
+        test(str(error), message)
+    else:
+        assert False, "no exception was thrown"
+
+
+test_error(
+    [
+        {
+            "values": {
+                "c++17": {
+                    "197001": [
+                        {
+                            "implemented": False,
+                        },
+                    ],
+                },
+            },
+            "headers": [],
+        },
+    ],
+    KeyError,
+    "'name'",
+)
+
+test_error(
+    [
+        {
+            "name": "a",
+            "headers": [],
+        },
+    ],
+    KeyError,
+    "'values'",
+)
+
+test_error(
+    [
+        {
+            "name": "a",
+            "values": {},
+            "headers": [],
+        },
+    ],
+    AssertionError,
+    "'values' is empty",
+)
+
+
+test_error(
+    [
+        {
+            "name": "a",
+            "values": {
+                "c++17": {},
+            },
+            "headers": [],
+        },
+    ],
+    AssertionError,
+    "a[c++17] has no entries",
+)
+
+test_error(
+    [
+        {
+            "name": "a",
+            "values": {
+                "c++17": {
+                    "197001": [
+                        {},
+                    ],
+                },
+            },
+            "headers": [],
+        },
+    ],
+    KeyError,
+    "'implemented'",
+)

libcxx/test/libcxx/feature_test_macro/standard_ftms.sh.py

@@ -0,0 +1,54 @@
+# ===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# ===----------------------------------------------------------------------===##
+
+# RUN: %{python} %s %{libcxx-dir}/utils %{libcxx-dir}/test/libcxx/feature_test_macro/test_data.json
+
+import sys
+
+sys.path.append(sys.argv[1])
+from generate_feature_test_macro_components import FeatureTestMacros
+
+
+def test(output, expected):
+    assert output == expected, f"expected\n{expected}\n\noutput\n{output}"
+
+
+ftm = FeatureTestMacros(sys.argv[2])
+test(
+    ftm.standard_ftms,
+    {
+        "__cpp_lib_any": {
+            "c++17": "201606L",
+            "c++20": "201606L",
+            "c++23": "201606L",
+            "c++26": "201606L",
+        },
+        "__cpp_lib_barrier": {
+            "c++20": "201907L",
+            "c++23": "201907L",
+            "c++26": "201907L",
+        },
+        "__cpp_lib_format": {
+            "c++20": "202110L",
+            "c++23": "202207L",
+            "c++26": "202311L",
+        },
+        "__cpp_lib_parallel_algorithm": {
+            "c++17": "201603L",
+            "c++20": "201603L",
+            "c++23": "201603L",
+            "c++26": "201603L",
+        },
+        "__cpp_lib_variant": {
+            "c++17": "202102L",
+            "c++20": "202106L",
+            "c++23": "202106L",
+            "c++26": "202306L",
+        },
+    },
+)

libcxx/test/libcxx/feature_test_macro/std_dialects.sh.py

@@ -0,0 +1,30 @@
+# ===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# ===----------------------------------------------------------------------===##
+
+# RUN: %{python} %s %{libcxx-dir}/utils %{libcxx-dir}/test/libcxx/feature_test_macro/test_data.json
+
+import sys
+
+sys.path.append(sys.argv[1])
+from generate_feature_test_macro_components import FeatureTestMacros
+
+
+def test(output, expected):
+    assert output == expected, f"expected\n{expected}\n\noutput\n{output}"
+
+
+ftm = FeatureTestMacros(sys.argv[2])
+test(
+    ftm.std_dialects,
+    [
+        "c++17",
+        "c++20",
+        "c++23",
+        "c++26",
+    ],
+)