MIR-borrowck: immutable unique closure upvars can be mutated #46236

davidtwco · 2017-11-24T13:04:01Z

Fixes #46023 and #46160 (see this comment).

rust-highfive · 2017-11-24T13:04:13Z

(rust_highfive has picked a reviewer for you, use r? to override)

davidtwco · 2017-11-24T13:04:44Z

This isn't quite working yet and I'm not quite sure why. I think I've followed the instructions left on the issue correctly.

r? @nikomatsakis @arielb1

arielb1 · 2017-11-25T20:29:28Z

src/librustc/mir/mod.rs

@@ -544,8 +544,8 @@ impl<'tcx> LocalDecl<'tcx> {
 pub struct UpvarDecl {
    pub debug_name: Name,

-    /// If true, the capture is behind a reference.
-    pub by_ref: bool
+    /// If None then the capture is by-value.


nit: rename it to pub capture_mode: Option<BorrowKind>?

arielb1 · 2017-11-25T20:34:56Z

src/librustc_mir/borrow_check.rs

+
+                                        if let Some(field) = field_projection {
+                                            let decl = &self.mir.upvar_decls[field.index()];
+                                            if let Some(borrow_kind) = decl.by_ref {


nit: if let Some(BorrowKind::Unique) = decl.by_ref {

arielb1 · 2017-11-25T20:45:12Z

I think you also need to change check_if_reassignment_to_immutable_state to use the new is_mutable logic - it handles error reporting for unique-immutable assignments. Otherwise assignments will not quite work. I think that's why the test is broken.

davidtwco · 2017-11-26T19:06:15Z

Pushed an alternate approach after speaking with @arielb1 on Gitter - it isn't working yet but I think I've implemented the mutability field in UpvarDecl as per our conversation.

arielb1 · 2017-11-27T14:34:02Z

src/librustc_mir/borrow_check.rs

+        };
+
+        if let Lvalue::Static(_) = lvalue {
+            self.report_assignment_to_static(context, (lvalue, span));
        }

        if let Some(mpi) = self.move_path_for_lvalue(lvalue) {


You still need the move_path_closest_to change here. Also, for assignments you want to move_path_closest_to the original lvalue, not the result of is_mutable, in order to allow

fn main() { let x: (u32, u32); x.0 = 0; x.1 = 1; }

arielb1 · 2017-11-27T14:50:16Z

@davidtwco

BTW, if you're already at this, you could also fix #46160 by marking the closure argument (argument _1 of a closure) as mutable

davidtwco · 2017-11-27T20:51:25Z

I've not done much testing of what I just pushed, but I've added work from all the instruction provided over the past few days. It includes a rebase onto current master which included #46022 which @arielb1 said I might need.

bors · 2017-11-30T08:01:55Z

☔ The latest upstream changes (presumably #46041) made this pull request unmergeable. Please resolve the merge conflicts.

davidtwco · 2017-11-30T13:19:01Z

Pushed a compiling version of the last changes and rebased ontop of the current master. Wasn't sure what to use for the new parameter to is_mutable.

…sure

arielb1 · 2017-11-30T23:21:11Z

@bors r+

bors · 2017-11-30T23:21:13Z

📌 Commit c6b1ba5 has been approved by arielb1

bors · 2017-12-01T13:26:16Z

⌛ Testing commit c6b1ba5 with merge e3ed212...

MIR-borrowck: immutable unique closure upvars can be mutated Fixes #46023 and #46160 (see [this comment](#46236 (comment))).

bors · 2017-12-01T16:01:17Z

☀️ Test successful - status-appveyor, status-travis
Approved by: arielb1
Pushing e3ed212 to master...

eddyb · 2018-05-16T11:02:47Z

This should have been merged like this, UpvarDecl was "supposed" to be debuginfo-only 😞.
But I'm not sure where to put this information - presumably it belongs attached to the closure type.

nikomatsakis · 2018-05-16T12:08:19Z

@eddyb

But I'm not sure where to put this information - presumably it belongs attached to the closure type

Hmm. Maybe, but I'm not sure. I guess it depends on how you view the mut information. I don't think of it as part of the type system, but rather a kind of lint that sits on top. But I suppose we do issue hard errors and so forth, so it's reasonable to view it as information that belongs in the closure type. It's sort of nice though that the "closure subst" is just types right now, and I'm not sure I want to change that. Another option would be to add some closure_upvar_info query that takes a closure def-id and gives further information, though — sort of like the existing free_vars calculation?

(On the other hand, maybe it's nice to have all the upvar information collected in one place...)

( <grumpy> I still think we should just drop the notion of declaring local variables as mut altogether. =) </grumpy> )

rust-highfive assigned pnkfelix Nov 24, 2017

rust-highfive assigned arielb1 and unassigned pnkfelix Nov 24, 2017

kennytm added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 24, 2017

arielb1 reviewed Nov 25, 2017

View reviewed changes

arielb1 reviewed Nov 27, 2017

View reviewed changes

davidtwco added 4 commits November 30, 2017 23:15

Added test for immutable unique closure upvar mutation.

347f631

Added test for spurious cannot borrow immutable item error with a clo…

c3459b0

…sure

Immutable unique closure upvars cannot be mutated.

dedbb4e

Fixed spurious cannot borrow immutable item error with a closure.

c6b1ba5

davidtwco changed the title ~~WIP: MIR-borrowck: immutable unique closure upvars can be mutated~~ MIR-borrowck: immutable unique closure upvars can be mutated Nov 30, 2017

bors added a commit that referenced this pull request Dec 1, 2017

Auto merge of #46236 - davidtwco:issue-46023, r=arielb1

e3ed212

MIR-borrowck: immutable unique closure upvars can be mutated Fixes #46023 and #46160 (see [this comment](#46236 (comment))).

bors merged commit c6b1ba5 into rust-lang:master Dec 1, 2017

This was referenced Dec 1, 2017

NLL: improve inference with flow results, represent regions with bitsets, and more #46319

Merged

MIR: change "lvalue" terminology to "place". #46425

Merged

davidtwco deleted the issue-46023 branch December 1, 2017 16:20

davidtwco mentioned this pull request Dec 1, 2017

MIR borrowck: spurious cannot borrow immutable item error with a closure #46160

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MIR-borrowck: immutable unique closure upvars can be mutated #46236

MIR-borrowck: immutable unique closure upvars can be mutated #46236

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eddyb commented May 16, 2018

nikomatsakis commented May 16, 2018

MIR-borrowck: immutable unique closure upvars can be mutated #46236

MIR-borrowck: immutable unique closure upvars can be mutated #46236

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