[-Wunsafe-buffer-usage] Replace assert that declarations are always found

Differential Revision: https://reviews.llvm.org/D157018

Author: t-rasmud

clang/lib/Analysis/UnsafeBufferUsage.cpp

@@ -888,7 +888,8 @@ class DeclUseTracker {
 
   const DeclStmt *lookupDecl(const VarDecl *VD) const {
     auto It = Defs.find(VD);
-    assert(It != Defs.end() && "Definition never discovered!");
+    if (It == Defs.end())
+      return nullptr;
     return It->second;
   }
 };
@@ -2053,7 +2054,10 @@ static FixItList fixVariableWithSpan(const VarDecl *VD,
                                      ASTContext &Ctx,
                                      UnsafeBufferUsageHandler &Handler) {
   const DeclStmt *DS = Tracker.lookupDecl(VD);
-  assert(DS && "Fixing non-local variables not implemented yet!");
+  if (!DS) {
+    DEBUG_NOTE_DECL_FAIL(VD, " : variables declared this way not implemented yet");
+    return {};
+  }
   if (!DS->isSingleDecl()) {
     // FIXME: to support handling multiple `VarDecl`s in a single `DeclStmt`
     DEBUG_NOTE_DECL_FAIL(VD, " : multiple VarDecls");

clang/test/SemaCXX/warn-unsafe-buffer-usage-debug.cpp

@@ -66,3 +66,15 @@ void implied_unclaimed_var(int *b) {  // expected-warning{{'b' is an unsafe poin
   b++;  // expected-note{{used in pointer arithmetic here}} \
         // debug-note{{safe buffers debug: failed to produce fixit for 'b' : has an unclaimed use}}
 }
+
+int *a = new int[3];  // expected-warning{{'a' is an unsafe pointer used for buffer access}} \
+// debug-note{{safe buffers debug: failed to produce fixit for 'a' : neither local nor a parameter}}
+void test_globals() {
+  a[7] = 4;  // expected-note{{used in buffer access here}}
+}
+
+void test_decomp_decl() {
+  int a[2] = {1, 2};
+  auto [x, y] = a;
+  x = 9;
+}