[clang] Respect the [[clang::unsafe_buffer_usage]] attribute for constructors (PR #91777)

[Artem Dergachev via cfe-commits]

================
@@ -921,10 +937,55 @@ class UnsafeBufferUsageAttrGadget : public WarningGadget {
   }
 
   static Matcher matcher() {
-    return stmt(callExpr(callee(functionDecl(hasAttr(attr::UnsafeBufferUsage))))
-                    .bind(OpTag));
+    auto HasUnsafeFnDecl =
+        callee(functionDecl(hasAttr(attr::UnsafeBufferUsage)));
+    return stmt(callExpr(HasUnsafeFnDecl).bind(OpTag));
+  }
+
+  void handleUnsafeOperation(UnsafeBufferUsageHandler &Handler,
+                             bool IsRelatedToDecl,
+                             ASTContext &Ctx) const override {
+    Handler.handleUnsafeOperation(Op, IsRelatedToDecl, Ctx);
+  }
+  SourceLocation getSourceLoc() const override { return Op->getBeginLoc(); }
+
+  DeclUseList getClaimedVarUseSites() const override { return {}; }
+};
+
+/// A call of a constructor that performs unchecked buffer operations
+/// over one of its pointer parameters, or constructs a class object that will
+/// perform buffer operations that depend on the correctness of the parameters.
+class UnsafeBufferUsageCtorAttrGadget : public WarningGadget {
+  constexpr static const char *const OpTag = "cxx_construct_expr";
+  const CXXConstructExpr *Op;
+
+public:
+  UnsafeBufferUsageCtorAttrGadget(const MatchFinder::MatchResult &Result)
+      : WarningGadget(Kind::UnsafeBufferUsageCtorAttr),
+        Op(Result.Nodes.getNodeAs<CXXConstructExpr>(OpTag)) {}
+
+  static bool classof(const Gadget *G) {
+    return G->getKind() == Kind::UnsafeBufferUsageCtorAttr;
+  }
+
+  static Matcher matcher() {
+    auto HasUnsafeCtorDecl =
+        hasDeclaration(cxxConstructorDecl(hasAttr(attr::UnsafeBufferUsage)));
+    // std::span(ptr, size) ctor is handled by SpanTwoParamConstructorGadget.
+    auto HasTwoParamSpanCtorDecl = hasDeclaration(
----------------
haoNoQ wrote:

I wouldn't mind something like
```
auto HasTwoParamSpanCtorDecl = SpanTwoParamConstructorGadget::matcher();
```
to prevent it from diverging when the other gadget changes. (We could build a fancier conflict resolution system but I don't think it's necessary yet.)

https://github.com/llvm/llvm-project/pull/91777