[libc++] Adds a new feature-test macro generator class.

[mordante]

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 #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.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Mark de Wever (mordante)

Changes

This is a proof-of-concept how we can test the script. Instead of storing the data in the script it's stored in a JSON file so a different file can be used for testing.

This is related to the RFC #89499

---

Full diff: https://github.com/llvm/llvm-project/pull/90889.diff

3 Files Affected:

• (added) libcxx/test/libcxx/feature_test_macro_csv.sh.py (+35)
• (added) libcxx/utils/data/feature_test_macros/test_data.json (+136)
• (modified) libcxx/utils/generate_feature_test_macro_components.py (+33)

diff --git a/libcxx/test/libcxx/feature_test_macro_csv.sh.py b/libcxx/test/libcxx/feature_test_macro_csv.sh.py
new file mode 100644
index 00000000000000..2d80bfad63c859
--- /dev/null
+++ b/libcxx/test/libcxx/feature_test_macro_csv.sh.py
@@ -0,0 +1,35 @@
+# RUN: %{python} %s %{libcxx-dir}/utils %{libcxx-dir}/utils/data/feature_test_macros/test_data.json
+
+import sys
+import json
+
+sys.path.append(sys.argv[1])
+from generate_feature_test_macro_components import get_table
+
+
+data = json.load(open(f"{sys.argv[2]}"))
+table = get_table(data)
+
+expected = {
+    "__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": "",
+        "c++23": "",
+        "c++26": "",
+    },
+    "__cpp_lib_variant": {
+        "c++17": "202102L",
+        "c++20": "202102L",
+        "c++23": "202102L",
+        "c++26": "202102L",
+    },
+}
+
+
+assert table == expected, f"expected\n{expected}\n\nresult\n{table}"
diff --git a/libcxx/utils/data/feature_test_macros/test_data.json b/libcxx/utils/data/feature_test_macros/test_data.json
new file mode 100644
index 00000000000000..5a98fba6403c09
--- /dev/null
+++ b/libcxx/utils/data/feature_test_macros/test_data.json
@@ -0,0 +1,136 @@
+[
+  {
+    "name": "__cpp_lib_any",
+    "values": {
+      "c++17": {
+        "201606": [
+          {
+            "implemented": true
+          }
+        ]
+      }
+    },
+    "headers": [
+      "any"
+    ]
+  },
+  {
+    "name": "__cpp_lib_barrier",
+    "values": {
+      "c++20": {
+        "201907": [
+          {
+            "implemented": true
+          }
+        ]
+      }
+    },
+    "headers": [
+      "barrier"
+    ],
+    "test_suite_guard":
+        "!defined(_LIBCPP_HAS_NO_THREADS) && (!defined(_LIBCPP_VERSION) || _LIBCPP_AVAILABILITY_HAS_SYNC)",
+    "libcxx_guard": "!defined(_LIBCPP_HAS_NO_THREADS) && _LIBCPP_AVAILABILITY_HAS_SYNC"
+  },
+  {
+    "name": "__cpp_lib_format",
+    "values": {
+      "c++20": {
+        "201907": [
+          {
+            "number": "P0645R10",
+            "title": "Text Formatting",
+            "implemented": true
+          },
+          {
+            "number": "P1361R2",
+            "title": "Integration of chrono with text formatting",
+            "implemented": false
+          }
+        ],
+        "202106": [
+          {
+            "number": "P2216R3",
+            "title": "std::format improvements",
+            "implemented": true
+          }
+        ],
+        "202110": [
+          {
+            "number": "P2372R3",
+            "title": "Fixing locale handling in chrono formatters",
+            "implemented": false
+          },
+          {
+            "number": "P2418R2",
+            "title": "FAdd support for std::generator-like types to std::format",
+            "implemented": true
+          }
+        ]
+      },
+      "c++23": {
+        "202207": [
+          {
+            "number": "P2419R2",
+            "title": "Clarify handling of encodings in localized formatting of chrono types",
+            "implemented": false
+          }
+        ]
+      },
+      "c++26": {
+        "202306": [
+          {
+            "number": "P2637R3",
+            "title": "Member Visit",
+            "implemented": true
+          }
+        ],
+        "202311": [
+          {
+            "number": "P2918R2",
+            "title": "Runtime format strings II",
+            "implemented": true
+          }
+        ]
+      }
+    },
+    "headers": [
+      "format"
+    ]
+  },
+  {
+    "name": "__cpp_lib_variant",
+    "values": {
+      "c++17": {
+        "202102": [
+          {
+            "number": "",
+            "title": "``std::visit`` for classes derived from ``std::variant``",
+            "implemented": true
+          }
+        ]
+      },
+      "c++20": {
+        "202106": [
+          {
+            "number": "",
+            "title": "Fully constexpr ``std::variant``",
+            "implemented": false
+          }
+        ]
+      },
+      "c++26": {
+        "202306": [
+          {
+            "number": "",
+            "title": "Member visit",
+            "implemented": true
+          }
+        ]
+      }
+    },
+    "headers": [
+      "variant"
+    ]
+  }
+]
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index f2b8d55c0e11b0..04a8a8786b1a35 100755
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -3,6 +3,7 @@
 import os
 from builtins import range
 from functools import reduce
+import json
 
 
 def get_libcxx_paths():
@@ -1857,6 +1858,38 @@ def produce_docs():
         f.write(doc_str)
 
 
+def get_table(data):
+    result = dict()
+    for feature in data:
+        last = None
+        entry = dict()
+        implemented = True
+        for std in get_std_dialects():
+            if std not in feature["values"].keys():
+                if last == None:
+                    continue
+                else:
+                    entry[std] = last
+            else:
+                if last == None:
+                    last = ""
+                if implemented:
+                    for value in feature["values"][std]:
+                        for paper in list(feature["values"][std][value]):
+                            if not paper["implemented"]:
+                                implemented = False
+                                break
+                        if implemented:
+                            last = f"{value}L"
+                        else:
+                            break
+
+                entry[std] = last
+        result[feature["name"]] = entry
+
+    return result
+
+
 def main():
     produce_version_header()
     produce_tests()

[EricWF]

Looks good to me.

[ldionne]

The approach LGTM but I'd like to see this again!

[ldionne]

This looks nice! I have some comments but this should be good to go then.

[ldionne]

LGTM w/ comments.