Bug 19965 – [DIP1000] Template allows to escape internal pointer

The following code compiles successfully with DIP1000 enabled: struct Buffer { int[10] data; int[] getData() @safe return { return data[]; } } struct Foo() { Buffer buffer; int[] toArray() @safe return { return buffer.getData; } } int[] a; void main() @safe { Foo!() f; a = f.toArray; } In the above example, a pointer to `data` (through the dynamic array returned by `getData`) is escaped to `a`. If `Foo` is not a template the code fails to compile, as expected.

If narrowed this issue down to this line in the DMD source code: https://github.com/dlang/dmd/blob/0459e34e20a0631a021550431dfe2411ebe16d3f/src/dmd/escape.d#L1465 When `Foo` is a template, `tf.isscope` is `true`, but when `Foo` is not a template `tf.isscope` is `false`. `isscope` is set to *true` at https://github.com/dlang/dmd/blob/0459e34e20a0631a021550431dfe2411ebe16d3f/src/dmd/semantic3.d#L1316 It is set to *true` because `funcdecl.vthis.storage_class` is `STC.maybescope`. That's as far as I got.

The problem appears to be with `scope` inference. In `escape.d` there are many places where `STC.maybescope` is removed after it has been determined that `scope` cannot be inferred. There is even a function `notMaybeScope` to do this. I believe all that needs to be done is to call `notMaybeScope(v)` in the right place and for the right conditions so `scope` is no longer inferred for this scenario.

Attempted Fix: https://github.com/dlang/dmd/pull/10334

dlang/dmd pull request #10334 "Fix Issue 19965 - [DIP1000] Template allows to escape internal pointer" was merged into master: - e5cc7453b4173d9408ad1efd115f74c720caaa4b by Mike: Fix Issue 19965 - [DIP1000] Template allows to escape internal pointer https://github.com/dlang/dmd/pull/10334