[LLVM][Support] Allow char[N] parameters in llvm::format
#159541
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@llvm/pr-subscribers-llvm-support Author: Tomohiro Kashiwada (kikairoya) ChangesCygwin builds are currently broken after #157312, which effectively reverted #138117. The root cause is that Cygwin defines This patch allows Other array types remain rejected:
Full diff: https://github.com/llvm/llvm-project/pull/159541.diff 3 Files Affected:
diff --git a/llvm/include/llvm/Support/Format.h b/llvm/include/llvm/Support/Format.h
index 2553002b37899..6cd73a213177d 100644
--- a/llvm/include/llvm/Support/Format.h
+++ b/llvm/include/llvm/Support/Format.h
@@ -78,6 +78,7 @@ class LLVM_ABI format_object_base {
/// printed, this synthesizes the string into a temporary buffer provided and
/// returns whether or not it is big enough.
+namespace detail {
// Helper to validate that format() parameters are scalars or pointers.
template <typename... Args> struct validate_format_parameters;
template <typename Arg, typename... Args>
@@ -88,9 +89,19 @@ struct validate_format_parameters<Arg, Args...> {
};
template <> struct validate_format_parameters<> {};
+template <typename T> struct decay_if_c_char_array {
+ using type = T;
+};
+template <std::size_t N> struct decay_if_c_char_array<char[N]> {
+ using type = const char *;
+};
+template <typename T>
+using decay_if_c_char_array_t = typename decay_if_c_char_array<T>::type;
+} // namespace detail
+
template <typename... Ts>
class format_object final : public format_object_base {
- std::tuple<Ts...> Vals;
+ std::tuple<detail::decay_if_c_char_array_t<Ts>...> Vals;
template <std::size_t... Is>
int snprint_tuple(char *Buffer, unsigned BufferSize,
@@ -105,7 +116,8 @@ class format_object final : public format_object_base {
public:
format_object(const char *fmt, const Ts &... vals)
: format_object_base(fmt), Vals(vals...) {
- validate_format_parameters<Ts...>();
+ detail::validate_format_parameters<
+ detail::decay_if_c_char_array_t<Ts>...>();
}
int snprint(char *Buffer, unsigned BufferSize) const override {
diff --git a/llvm/unittests/Support/CMakeLists.txt b/llvm/unittests/Support/CMakeLists.txt
index d1dfb1dc4a722..1f2a68545d107 100644
--- a/llvm/unittests/Support/CMakeLists.txt
+++ b/llvm/unittests/Support/CMakeLists.txt
@@ -44,6 +44,7 @@ add_llvm_unittest(SupportTests
ExtensibleRTTITest.cpp
FileCollectorTest.cpp
FileOutputBufferTest.cpp
+ Format.cpp
FormatVariadicTest.cpp
FSUniqueIDTest.cpp
GenericDomTreeTest.cpp
diff --git a/llvm/unittests/Support/Format.cpp b/llvm/unittests/Support/Format.cpp
new file mode 100644
index 0000000000000..c4e421fe9dc4c
--- /dev/null
+++ b/llvm/unittests/Support/Format.cpp
@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Format.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+template <typename FormatTy>
+std::string printToString(unsigned MaxN, FormatTy &&Fmt) {
+ std::vector<char> Dst(MaxN + 2);
+ int N = Fmt.snprint(Dst.data(), Dst.size());
+ Dst.back() = 0;
+ return N < 0 ? "" : Dst.data();
+}
+
+template <typename Expected, typename Arg>
+constexpr bool checkDecayTypeEq(const Arg &arg) {
+ return std::is_same_v<detail::decay_if_c_char_array_t<Arg>, Expected>;
+}
+
+TEST(Format, DecayIfCCharArray) {
+ char Array[] = "Array";
+ const char ConstArray[] = "ConstArray";
+ char PtrBuf[] = "Ptr";
+ char *Ptr = PtrBuf;
+ const char *PtrToConst = "PtrToConst";
+
+ EXPECT_EQ(" Literal", printToString(20, format("%15s", "Literal")));
+ EXPECT_EQ(" Array", printToString(20, format("%15s", Array)));
+ EXPECT_EQ(" ConstArray", printToString(20, format("%15s", ConstArray)));
+ EXPECT_EQ(" Ptr", printToString(20, format("%15s", Ptr)));
+ EXPECT_EQ(" PtrToConst", printToString(20, format("%15s", PtrToConst)));
+
+ EXPECT_TRUE(checkDecayTypeEq<const char *>("Literal"));
+ EXPECT_TRUE(checkDecayTypeEq<const char *>(Array));
+ EXPECT_TRUE(checkDecayTypeEq<const char *>(ConstArray));
+ EXPECT_TRUE(checkDecayTypeEq<char *>(Ptr));
+ EXPECT_TRUE(checkDecayTypeEq<const char *>(PtrToConst));
+ EXPECT_TRUE(checkDecayTypeEq<char>(PtrToConst[0]));
+ EXPECT_TRUE(
+ checkDecayTypeEq<const char *>(static_cast<const char *>("Literal")));
+
+ wchar_t WCharArray[] = L"WCharArray";
+ EXPECT_TRUE(checkDecayTypeEq<wchar_t[11]>(WCharArray));
+ EXPECT_TRUE(checkDecayTypeEq<wchar_t>(WCharArray[0]));
+}
+
+} // namespace
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ping |
Cygwin builds are currently broken after llvm#157312, which effectively reverted llvm#138117. The root cause is that Cygwin defines `DL_info::dli_fname` as `char[N]`, which is not a valid parameter type for `llvm::format`. This patch allows `llvm::format` to accept `char[N]` by decaying it to `const char *`. As a result, string literals are also accepted without an explicit cast. Other array types remain rejected: - Wide/unicode character arrays (e.g., `wchar_t[N]`) are not supported, as LLVM does not use them and they are less compatible with platform's `printf` implementations. - Non-character arrays (e.g., `int[N]`) are also rejected, since passing such arrays to `printf` is meaningless.
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ping. @kazutakahirata @tgymnich Could you please take a look at this? |
kazutakahirata
approved these changes
Oct 12, 2025
kuhar
approved these changes
Oct 13, 2025
tgymnich
approved these changes
Oct 13, 2025
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Thank you for the reviewing and merging this! |
DharuniRAcharya
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Oct 13, 2025
…9541) Cygwin builds are currently broken after llvm#157312, which effectively reverted llvm#138117. The root cause is that Cygwin defines `DL_info::dli_fname` as `char[N]`, which is not a valid parameter type for `llvm::format`. This patch allows `llvm::format` to accept `char[N]` by decaying it to `const char *`. As a result, string literals are also accepted without an explicit cast. Other array types remain rejected: - Wide/unicode character arrays (e.g., `wchar_t[N]`) are not supported, as LLVM does not use them and they are less compatible with platform's `printf` implementations. - Non-character arrays (e.g., `int[N]`) are also rejected, since passing such arrays to `printf` is meaningless.
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/168/builds/16618 Here is the relevant piece of the build log for the reference |
akadutta
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Oct 14, 2025
…9541) Cygwin builds are currently broken after llvm#157312, which effectively reverted llvm#138117. The root cause is that Cygwin defines `DL_info::dli_fname` as `char[N]`, which is not a valid parameter type for `llvm::format`. This patch allows `llvm::format` to accept `char[N]` by decaying it to `const char *`. As a result, string literals are also accepted without an explicit cast. Other array types remain rejected: - Wide/unicode character arrays (e.g., `wchar_t[N]`) are not supported, as LLVM does not use them and they are less compatible with platform's `printf` implementations. - Non-character arrays (e.g., `int[N]`) are also rejected, since passing such arrays to `printf` is meaningless.
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Cygwin builds are currently broken after #157312, which effectively reverted #138117. The root cause is that Cygwin defines
DL_info::dli_fnameaschar[N], which is not a valid parameter type forllvm::format.This patch allows
llvm::formatto acceptchar[N]by decaying it toconst char *. As a result, string literals are also accepted without an explicit cast.Other array types remain rejected:
wchar_t[N]) are not supported, as LLVM does not use them and they are less compatible with platform'sprintfimplementations.int[N]) are also rejected, since passing such arrays toprintfis meaningless.