[-Wunsafe-buffer-usage] Fixits for assignment to array subscript expr

[ziqingluo-90]

Summary

Generalizing the shared "element-type" context means existing Fixables will emit Fix-Its for new cases.

[jkorous]

rebased

[NoQ]

Looks great!

clang/lib/Analysis/UnsafeBufferUsage.cpp

127

I think anyOf is appropriate because the same expression cannot ever match both implicitCastExpr and binaryOperator at once, so we want this to short circuit.

[ziqingluo-90]

Taking care of this patch on behalf of @jkorous.

[ziqingluo-90]

Addressing comments

[NoQ]

Aha ok LGTM!

clang/lib/Analysis/UnsafeBufferUsage.cpp

 }
 
 AST_MATCHER_P(CastExpr, castSubExpr, internal::Matcher<Expr>, innerMatcher) {
   return innerMatcher.matches(*Node.getSubExpr(), Finder, Builder);
 }
 
 // Returns a matcher that matches any expression 'e' such that `innerMatcher`
 // matches 'e' and 'e' is in an Unspecified Lvalue Context.
-static internal::Matcher<Stmt>
-isInUnspecifiedLvalueContext(internal::Matcher<Expr> innerMatcher) {
-  return implicitCastExpr(hasCastKind(CastKind::CK_LValueToRValue),
-                          castSubExpr(innerMatcher));
-  // FIXME: add assignmentTo context...
+static auto isInUnspecifiedLvalueContext(internal::Matcher<Expr> innerMatcher) {
+// clang-format off
+  return
+    expr(eachOf(
+      implicitCastExpr(
+        hasCastKind(CastKind::CK_LValueToRValue),
+        castSubExpr(innerMatcher)),
+      binaryOperator(
+        hasAnyOperatorName("="),
+        hasLHS(innerMatcher)
+      )
+    ));
+// clang-format off
 }
 } // namespace clang::ast_matchers
 
 namespace {
 // Because the analysis revolves around variables and their types, we'll need to
 // track uses of variables (aka DeclRefExprs).
 using DeclUseList = SmallVector<const DeclRefExpr *, 1>;
 

clang/test/SemaCXX/warn-unsafe-buffer-usage-fixits-assign-to-array-subscr-on-ptr.cpp

+// RUN: %clang_cc1 -std=c++20 -Wunsafe-buffer-usage -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+
+// TODO cases where we don't want fixits
+
+// The Fix-It for unsafe operation is trivially empty.
+// In order to test that our machinery recognizes that we can test if the variable declaration gets a Fix-It.
+// If the operation wasn't handled propertly the declaration won't get Fix-It.
+// By testing presence of the declaration Fix-It we indirectly test presence of the trivial Fix-It for its operations.
+void test() {
+  int *p = new int[10];
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:3-[[@LINE-1]]:11}:"std::span<int> p"
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-2]]:12-[[@LINE-2]]:12}:"{"
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:23-[[@LINE-3]]:23}:", 10}"
+  p[5] = 1;
+  // CHECK-NOT: fix-it:
+}