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

[Rohan Jacob-Rao via cfe-commits]

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@@ -699,6 +699,45 @@ static bool isSafeSpanTwoParamConstruct(const CXXConstructExpr &Node,
   return isPtrBufferSafe(Arg0, Arg1, Ctx);
 }
 
+static bool isSafeStringViewTwoParamConstruct(const CXXConstructExpr &Node,
+                                              ASTContext &Ctx) {
+  const Expr *Arg0 = Node.getArg(0)->IgnoreParenImpCasts();
+  const Expr *Arg1 = Node.getArg(1)->IgnoreParenImpCasts();
+
+  // Pattern 1: String Literals (Safe if size <= length)
+  if (const auto *SL = dyn_cast<StringLiteral>(Arg0)) {
+    if (auto ArgSize = Arg1->getIntegerConstantExpr(Ctx)) {
+      if (ArgSize->getZExtValue() <= SL->getLength())
+        return true;
+    }
+  }
+
+  // Pattern 2: Constant Arrays (Safe if exact match)
+  QualType T0 = Arg0->getType().getCanonicalType();
+  if (const auto *CAT = Ctx.getAsConstantArrayType(T0)) {
+   if (auto ArgSize = Arg1->getIntegerConstantExpr(Ctx)) {
+     // Wrap CAT->getSize() in APSInt to match ArgSize's type
+     if (llvm::APSInt::compareValues(llvm::APSInt(CAT->getSize(), /*isUnsigned=*/true), 
+                                    *ArgSize) == 0)
+       return true;
+   }
+ }
+
+  // Pattern 3: Zero length is safe
+  if (auto Val = Arg1->getIntegerConstantExpr(Ctx)) {
+    if (Val->isZero()) return true;
+  }
+
+  // Pattern 4: Pointer/Iterator Pair
+  QualType T1 = Arg1->getType().getCanonicalType();
+  if ((T0->isPointerType() && T1->isPointerType()) ||
+      (T0->isRecordType() && T1->isRecordType())) {
----------------
rohanjr wrote:

I noticed that `isSafeSpanTwoParamConstruct()` doesn't allow the iterator range constructor in general, only calls with `x.begin()` and `x.end()`. Should we do the same here or do you have a reason to allow arbitrary pointers/iterators? I see in your test that we get a separate warning for unsafe pointer arithmetic, but that might not cover all unsafe cases.

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