[clang] [Clang][UnsafeBufferUsage] Warn about two-arg string_view constructors. (PR #180471)

[Rohan Jacob-Rao via cfe-commits]

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@@ -1805,6 +1805,70 @@ class SpanTwoParamConstructorGadget : public WarningGadget {
   SmallVector<const Expr *, 1> getUnsafePtrs() const override { return {}; }
 };
 
+class StringViewTwoParamConstructorGadget : public WarningGadget {
+  static constexpr const char *const StringViewTwoParamConstructorTag =
+      "stringViewTwoParamConstructor";
+  const CXXConstructExpr *Ctor; // the string_view constructor expression
+
+public:
+  StringViewTwoParamConstructorGadget(const MatchResult &Result)
+      : WarningGadget(Kind::StringViewTwoParamConstructor),
+        Ctor(Result.getNodeAs<CXXConstructExpr>(
+            StringViewTwoParamConstructorTag)) {}
+
+  static bool classof(const Gadget *G) {
+    return G->getKind() == Kind::StringViewTwoParamConstructor;
+  }
+
+  static bool matches(const Stmt *S, ASTContext &Ctx, MatchResult &Result) {
+    const auto *CE = dyn_cast<CXXConstructExpr>(S);
+    if (!CE)
+      return false;
+    const auto *CDecl = CE->getConstructor();
+    const auto *CRecordDecl = CDecl->getParent();
+
+    // MATCH: std::basic_string_view
+    bool IsStringView =
+        CRecordDecl->isInStdNamespace() &&
+        CDecl->getDeclName().getAsString() == "basic_string_view" &&
+        CE->getNumArgs() == 2;
+
+    if (!IsStringView || isSafeSpanTwoParamConstruct(*CE, Ctx))
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rohanjr wrote:

Does reusing `isSafeSpanTwoParamConstruct` make sense for `string_view`? It looks like there's a subset of safe cases that would apply to `string_view`s. I would at least add some tests for the "safe" 2 parameter constructions.

https://github.com/llvm/llvm-project/pull/180471