[libcxx] [test] Detect the UCRT printf("%a") formatting bug

[mstorsjo]

This fixes testing with MinGW, if built without __USE_MINGW_ANSI_STDIO=1.

On x86 MinGW, such a configuration fails printf tests with long doubles due to mismatches between 80 and 64 bit long doubles - but on ARM, there's no such issue, so building without __USE_MINGW_ANSI_STDIO=1 is perfectly valid there.

Add another similar XFAIL to a libcxxabi test; this test isn't executed in MSVC environments, so no XFAIL has been needed so far.

[llvmbot]

@llvm/pr-subscribers-libcxxabi

@llvm/pr-subscribers-libcxx

Author: Martin Storsjö (mstorsjo)

Changes

This fixes testing with MinGW, if built without __USE_MINGW_ANSI_STDIO=1.

On x86 MinGW, such a configuration fails printf tests with long doubles due to mismatches between 80 and 64 bit long doubles - but on ARM, there's no such issue, so building without __USE_MINGW_ANSI_STDIO=1 is perfectly valid there.

Add another similar XFAIL to a libcxxabi test; this test isn't executed in MSVC environments, so no XFAIL has been needed so far.

---

Full diff: https://github.com/llvm/llvm-project/pull/99846.diff

4 Files Affected:

• (modified) libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.hex.pass.cpp (+1-4)
• (modified) libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.hex.pass.cpp (+1-4)
• (modified) libcxx/utils/libcxx/test/features.py (+20)
• (modified) libcxxabi/test/test_demangle.pass.cpp (+2)

diff --git a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.hex.pass.cpp b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.hex.pass.cpp
index 21efa978abdcc..946c26398fcb8 100644
--- a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.hex.pass.cpp
+++ b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.hex.pass.cpp
@@ -12,10 +12,7 @@
 
 // iter_type put(iter_type s, ios_base& iob, char_type fill, double v) const;
 
-// With the Microsoft UCRT, printf("%a", 0.0) produces "0x0.0000000000000p+0"
-// while other C runtimes produce just "0x0p+0".
-// https://developercommunity.visualstudio.com/t/Printf-formatting-of-float-as-hex-prints/1660844
-// XFAIL: msvc
+// XFAIL: win32-broken-printf-a-precision
 
 // XFAIL: LIBCXX-AIX-FIXME
 
diff --git a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.hex.pass.cpp b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.hex.pass.cpp
index c97c9a0c40369..a195c34e5f8e8 100644
--- a/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.hex.pass.cpp
+++ b/libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.hex.pass.cpp
@@ -12,10 +12,7 @@
 
 // iter_type put(iter_type s, ios_base& iob, char_type fill, long double v) const;
 
-// With the Microsoft UCRT, printf("%a", 0.0) produces "0x0.0000000000000p+0"
-// while other C runtimes produce just "0x0p+0".
-// https://developercommunity.visualstudio.com/t/Printf-formatting-of-float-as-hex-prints/1660844
-// XFAIL: msvc
+// XFAIL: win32-broken-printf-a-precision
 
 // XFAIL: LIBCXX-AIX-FIXME
 
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
index 5e708da4f8fbe..3393bd61a8483 100644
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -263,6 +263,26 @@ def _mingwSupportsModules(cfg):
           """,
         ),
     ),
+    # Check for a Windows UCRT bug (not fixed upstream yet).
+    # With UCRT, printf("%a", 0.0) produces "0x0.0000000000000p+0",
+    # while other C runtimes produce just "0x0p+0".
+    # https://developercommunity.visualstudio.com/t/Printf-formatting-of-float-as-hex-prints/1660844
+    Feature(
+        name='win32-broken-printf-a-precision',
+        when=lambda cfg: '_WIN32' in compilerMacros(cfg)
+        and not programSucceeds(
+            cfg,
+            """
+            #include <stdio.h>
+            #include <string.h>
+            int main(int, char**) {
+              char buf[100];
+              snprintf(buf, sizeof(buf), "%a", 0.0);
+              return strcmp(buf, "0x0p+0");
+            }
+          """,
+        ),
+    ),
     # Check for Glibc < 2.27, where the ru_RU.UTF-8 locale had
     # mon_decimal_point == ".", which our tests don't handle.
     Feature(
diff --git a/libcxxabi/test/test_demangle.pass.cpp b/libcxxabi/test/test_demangle.pass.cpp
index fe5598991b831..ab783cf9d96f2 100644
--- a/libcxxabi/test/test_demangle.pass.cpp
+++ b/libcxxabi/test/test_demangle.pass.cpp
@@ -17,6 +17,8 @@
 // 80-bit format, and this demangling test is failing on it.
 // XFAIL: LIBCXX-ANDROID-FIXME && target={{i686|x86_64}}-{{.+}}-android{{.*}}
 
+// XFAIL: win32-broken-printf-a-precision
+
 #include "support/timer.h"
 #include <algorithm>
 #include <cassert>

[github-actions]

✅ With the latest revision this PR passed the Python code formatter.

[mordante]

Thanks, LGTM!