Fix issue 22298 - Nested function's scope parameters can be assigned to variables in enclosing function

[dkorpel]

In the initial implementation of lifetimes (#5972), a __gshared counter was added that was incremented whenever a VarDeclaration was created. This is supposed to give a lexical order to local variables, but it fails because there are multiple stages where VarDeclarations are created:

• Simple local variables are generated in the parser
• Parameters are created in semantic3 of a FuncDeclaration
• Generated temporaries and variables from a string mixin are created during function body semantic

Special cases were added to VarDeclaration.enclosesLifetimeOf(VarDeclaration v), where temporaries were compared using line and column number, and parameters assumed that lifetime(parameter) > lifetime(local) always holds. Of course, this can fail when the parameter is from a nested function, and the local is in the enclosing function. It also doesn't account for mixin:

void foo() @safe 
{
    mixin("scope int* x;"); // sequence number 1 from semantic
    scope int* y; // sequence number 0 from parser
    x = y; // allowed, it thinks y has longer lifetime
}

I made the sequence counter increment during symbol semantic of the VarDeclaration instead of in the constructor, and moved the counter to the global struct so it can be reset easier. This is still hacky and not how I want to see lifetimes implemented, but it'll do for now.

[dlang-bot]

Thanks for your pull request and interest in making D better, @dkorpel! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22298	normal	[DIP1000] Nested function's scope parameters can be assigned to variables in enclosing function

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#13530"

[thewilsonator]

This is a memory safety issue, it should probably go to stable

[RazvanN7]

LGTM.

[MoonlightSentinel]

Is the check for STC.temp still necessary?

[dkorpel]

Maybe not, let's see what the test suite says.

[dkorpel]

std/datetime/systime.d(9085): Error: scope variable `__tup794` assigned to `foundTZ` with longer lifetime

Looks like it's still needed for tuple lowering.