fix Issue 17795 - [scope] Scope errors not detected in ~= operation

src/ddmd/escape.d

@@ -169,7 +169,7 @@ bool checkParamArgumentEscape(Scope* sc, FuncDeclaration fdc, Identifier par, Ex
  * to eliminate the error.
  * Params:
  *      sc = used to determine current function and module
- *      ae = AssignExp to check for any pointers to the stack
+ *      e = AssignExp or CatAssignExp to check for any pointers to the stack
  *      gag = do not print error messages
  * Returns:
  *      true if pointers to the stack can escape via assignment
@@ -178,9 +178,9 @@ bool checkAssignEscape(Scope* sc, Expression e, bool gag)
 {
     enum log = false;
     if (log) printf("checkAssignEscape(e: %s)\n", e.toChars());
-    if (e.op != TOKassign && e.op != TOKblit && e.op != TOKconstruct)
+    if (e.op != TOKassign && e.op != TOKblit && e.op != TOKconstruct && e.op != TOKcatass)
         return false;
-    auto ae = cast(AssignExp)e;
+    auto ae = cast(BinExp)e;
     Expression e1 = ae.e1;
     Expression e2 = ae.e2;
     //printf("type = %s, %d\n", e1.type.toChars(), e1.type.hasPointers());

src/ddmd/expressionsem.d

@@ -6731,7 +6731,7 @@ extern (C++) final class ExpressionSemanticVisitor : Visitor
             return;
         }
 
-        //printf("CatAssignExp::semantic() %s\n", toChars());
+        //printf("CatAssignExp::semantic() %s\n", exp.toChars());
         Expression e = exp.op_overload(sc);
         if (e)
         {
@@ -6772,13 +6772,20 @@ extern (C++) final class ExpressionSemanticVisitor : Visitor
         Type tb1next = tb1.nextOf();
         Type tb2 = exp.e2.type.toBasetype();
 
+        /* Two possibilities:
+         * 1. appending T[] to T[]
+         * 2. appending T to T[]
+         */
+        bool appendArray = false;       // assume case 2
+
         if ((tb1.ty == Tarray) &&
             (tb2.ty == Tarray || tb2.ty == Tsarray) &&
             (exp.e2.implicitConvTo(exp.e1.type) ||
              (tb2.nextOf().implicitConvTo(tb1next) &&
               (tb2.nextOf().size(Loc()) == tb1next.size(Loc())))))
         {
-            // Append array
+            // case 1: append array
+            appendArray = true;
             if (exp.e1.checkPostblit(sc, tb1next))
             {
                 result = new ErrorExp();
@@ -6822,7 +6829,10 @@ extern (C++) final class ExpressionSemanticVisitor : Visitor
         }
 
         exp.type = exp.e1.type;
-        result = exp.reorderSettingAAElem(sc);
+        auto res = exp.reorderSettingAAElem(sc);
+        if (!appendArray && global.params.vsafe)
+            checkAssignEscape(sc, res, false);
+        result = res;
     }
 
     override void visit(AddExp exp)

test/fail_compilation/retscope6.d

@@ -0,0 +1,23 @@
+/*
+REQUIRED_ARGS: -dip1000
+PERMUTE_ARGS:
+*/
+
+/*
+TEST_OUTPUT:
+---
+fail_compilation/retscope6.d(6007): Error: reference to local variable `i` assigned to non-scope `arr[0]`
+---
+*/
+
+#line 6000
+
+// https://issues.dlang.org/show_bug.cgi?id=17795
+
+int* test() @safe
+{
+    int i;
+    int*[][] arr = new int*[][](1);
+    arr[0] ~= &i;
+    return arr[0][0];
+}