[clang] [-Wunsafe-buffer-usage] Add a new warning for uses of std::span two-parameter constructors (PR #77148)

[via cfe-commits]

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@@ -594,6 +667,44 @@ class PointerArithmeticGadget : public WarningGadget {
   // FIXME: this gadge will need a fix-it
 };
 
+class SpanTwoParamConstructorGadget : public WarningGadget {
+  static constexpr const char *const SpanTwoParamConstructorTag =
+      "spanTwoParamConstructor";
+  const CXXConstructExpr *Ctor; // the span constructor expression
+
+public:
+  SpanTwoParamConstructorGadget(const MatchFinder::MatchResult &Result)
+      : WarningGadget(Kind::SpanTwoParamConstructor),
+        Ctor(Result.Nodes.getNodeAs<CXXConstructExpr>(
+            SpanTwoParamConstructorTag)) {}
+
+  static bool classof(const Gadget *G) {
+    return G->getKind() == Kind::SpanTwoParamConstructor;
+  }
+
+  static Matcher matcher() {
+    auto HasTwoParamSpanCtorDecl = hasDeclaration(
+        cxxConstructorDecl(hasDeclContext(isInStdNamespace()), hasName("span"),
+                           parameterCountIs(2)));
+
+    return stmt(cxxConstructExpr(HasTwoParamSpanCtorDecl,
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jkorous-apple wrote:

This is just a note, I don't see anything actionable for this patch.

I wonder if in the future we should have a smarter solution for the span constructor that takes 2 iterators for cases where the iterators are hardened.
subset of (3) here: https://en.cppreference.com/w/cpp/container/span/span

https://github.com/llvm/llvm-project/pull/77148