[clang-tools-extra] [clang-tidy] Fix `cppcoreguidelines-missing-std-forward` false positive for deleted functions (PR #83055)

[via cfe-commits]

https://github.com/AMS21 created https://github.com/llvm/llvm-project/pull/83055

A definition like this:

```cpp
template <typename T>
void f(T &&) = delete;
```

would previously generate the the following output:

```sh
<source>:2:12: warning: forwarding reference parameter '' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward]
    2 | void f(T &&) = delete;
      |            ^
1 warning generated.
```

[godbolt](https://godbolt.org/z/9d4Y9qeWW)

which is obviously not correct and this simple patch fixes that.

>From a47b09f62fcd8ae82b704851341a05b5ad2199fa Mon Sep 17 00:00:00 2001
From: AMS21 <AMS21.github at gmail.com>
Date: Mon, 26 Feb 2024 21:45:12 +0100
Subject: [PATCH] [clang-tidy] Fix `cppcoreguidelines-missing-std-forward`
 false positive for deleted functions

A definition like this:

```cpp
template <typename T>
void f(T &&) = delete;
```

would previously generate the the following output:

```sh
<source>:2:12: warning: forwarding reference parameter '' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward]
    2 | void f(T &&) = delete;
      |            ^
1 warning generated.
```

[godbolt](https://godbolt.org/z/9d4Y9qeWW)

which is obviously not correct and this simple patch fixes that.
---
 .../cppcoreguidelines/MissingStdForwardCheck.cpp  |  3 ++-
 clang-tools-extra/docs/ReleaseNotes.rst           |  4 ++++
 .../cppcoreguidelines/missing-std-forward.cpp     | 15 +++++++++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
index 370de12999aceb..c633683570f748 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
@@ -127,7 +127,8 @@ void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
                   hasAncestor(functionDecl().bind("func")),
                   hasAncestor(functionDecl(
                       isDefinition(), equalsBoundNode("func"), ToParam,
-                      unless(hasDescendant(std::move(ForwardCallMatcher)))))),
+                      unless(anyOf(isDeleted(), hasDescendant(std::move(
+                                                    ForwardCallMatcher))))))),
       this);
 }
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 69537964f9bce0..d1b841336f35c3 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -134,6 +134,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/unused-local-non-trivial-variable>` check by
   ignoring local variable with ``[maybe_unused]`` attribute.
 
+- Fixed :doc:`cppcoreguidelines-missing-std-forward
+  <clang-tidy/checks/cppcoreguidelines/missing-std-foward>` check giving false
+  positives for deleted functions.
+
 - Cleaned up :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>`
   by removing enforcement of rule `C.48
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
index 443f338ba2046a..20e43f04180ff3 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
@@ -173,3 +173,18 @@ void lambda_value_reference_auxiliary_var(T&& t) {
 }
 
 } // namespace negative_cases
+
+namespace deleted_functions {
+
+template <typename T>
+void f(T &&) = delete;
+
+struct S {
+    template <typename T>
+    S(T &&) = delete;
+
+    template <typename T>
+    void operator&(T &&) = delete;
+};
+
+} // namespace deleted_functions