fix Issue 20150 - -dip1000 defeated by pure

Author: aG0aep6G

src/dmd/mtype.d

@@ -4533,15 +4533,15 @@ extern (C++) final class TypeFunction : TypeNext
             }
         }
 
-        stc |= STC.scope_;
-
         /* Inferring STC.return_ here has false positives
          * for pure functions, producing spurious error messages
          * about escaping references.
          * Give up on it for now.
          */
         version (none)
         {
+            stc |= STC.scope_;
+
             Type tret = nextOf().toBasetype();
             if (isref || tret.hasPointers())
             {
@@ -4551,6 +4551,17 @@ extern (C++) final class TypeFunction : TypeNext
                 stc |= STC.return_;
             }
         }
+        else
+        {
+            // Check escaping through return value
+            Type tret = nextOf().toBasetype();
+            if (isref || tret.hasPointers())
+            {
+                return stc;
+            }
+
+            stc |= STC.scope_;
+        }
 
         return stc;
     }

test/fail_compilation/retscope6.d

@@ -198,3 +198,36 @@ void hmac(scope ubyte[] secret)
     ubyte[10] buffer;
     secret = buffer[];
 }
+
+/* TEST_OUTPUT:
+---
+fail_compilation/retscope6.d(12011): Error: reference to local variable `x` assigned to non-scope parameter `r` calling retscope6.escape_m_20150
+fail_compilation/retscope6.d(12022): Error: reference to local variable `x` assigned to non-scope parameter `r` calling retscope6.escape_c_20150
+---
+*/
+
+#line 12000
+
+// https://issues.dlang.org/show_bug.cgi?id=20150
+
+int* escape_m_20150(int* r) @safe pure
+{
+    return r;
+}
+
+int* f_m_20150() @safe
+{
+    int x = 42;
+    return escape_m_20150(&x);
+}
+
+const(int)* escape_c_20150(const int* r) @safe pure
+{
+    return r;
+}
+
+const(int)* f_c_20150() @safe
+{
+    int x = 42;
+    return escape_c_20150(&x);
+}