From e22f9c1fdd00f2ad3cfdd1dd7a67145eadc3b21c Mon Sep 17 00:00:00 2001
From: Dino Radakovic <dinor@google.com>
Date: Wed, 7 Feb 2024 07:26:02 -0800
Subject: `demangle`: Implement parsing for simplest constrained template
 arguments

C++20 introduced constraints, where concepts such as `std::integral` can be used to restrict template parameters:

```
template <std::integral T>
int foo(T t);  // Only accepts integral types.
```

Clang mangles these starting with a prefix `Tk`, followed by the concept name, which mangles as a type.
For example, compare `foo` and `bar` here: https://godbolt.org/z/Kzbrrchde

Note that this implementation doesn't cover the more complex case where the concept is templated too. See [llvm's implementation](https://github.com/llvm/llvm-project/commit/4b163e343cfa54c8d55c9da73c70d58f55ea9df2) and its tests for a thorough version.

PiperOrigin-RevId: 604976260
Change-Id: Ic116c5f6f27c3f7714638bdee8de11dce871f0be
---
 absl/debugging/internal/demangle_test.cc | 33 ++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

(limited to 'absl/debugging/internal/demangle_test.cc')

diff --git a/absl/debugging/internal/demangle_test.cc b/absl/debugging/internal/demangle_test.cc
index a16ab75e..c1b61253 100644
--- a/absl/debugging/internal/demangle_test.cc
+++ b/absl/debugging/internal/demangle_test.cc
@@ -31,6 +31,39 @@ namespace {
 
 using ::testing::ContainsRegex;
 
+TEST(Demangle, FunctionTemplate) {
+  char tmp[100];
+
+  // template <typename T>
+  // int foo(T);
+  //
+  // foo<int>(5);
+  ASSERT_TRUE(Demangle("_Z3fooIiEiT_", tmp, sizeof(tmp)));
+  EXPECT_STREQ(tmp, "foo<>()");
+}
+
+TEST(Demangle, FunctionTemplateWithNesting) {
+  char tmp[100];
+
+  // template <typename T>
+  // int foo(T);
+  //
+  // foo<Wrapper<int>>({ .value = 5 });
+  ASSERT_TRUE(Demangle("_Z3fooI7WrapperIiEEiT_", tmp, sizeof(tmp)));
+  EXPECT_STREQ(tmp, "foo<>()");
+}
+
+TEST(Demangle, FunctionTemplateWithConstraint) {
+  char tmp[100];
+
+  // template <std::integral T>
+  // int foo(T);
+  //
+  // foo<Wrapper<int>(5);
+  ASSERT_TRUE(Demangle("_Z3fooITkSt8integraliEiT_", tmp, sizeof(tmp)));
+  EXPECT_STREQ(tmp, "foo<>()");
+}
+
 // Test corner cases of boundary conditions.
 TEST(Demangle, CornerCases) {
   char tmp[10];
-- 
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