More restrictive 2 phase borrows - take 2

[matthewjasper]

Signal lint diagnostic mutable_borrow_reservation_conflict when borrow-check finds a 2-phase borrow's reservation overlapping with a shared borrow.

(pnkfelix updated description)

cc #56254 , #59159

blocks PR #59114

r? @pnkfelix

cc @RalfJung @nikomatsakis

[matthewjasper]

@bors try

[bors]

⌛ Trying commit 58d9280 with merge d7cd76545183ac4a130654fd5c03b5d3ef1287b2...

[bors]

💥 Test timed out

[matthewjasper]

@bors retry

[bors]

⌛ Trying commit 58d9280 with merge 684d1bd...

[bors]

☀️ Test successful - checks-travis
State: approved= try=True

[matthewjasper]

@rust-lang/infra can this have a check only crater run?

[pietroalbini]

You have the perms to request one yourself now 🎉

[matthewjasper]

@craterbot run start=master#fb162e69449b423c5aed0d9c39f6c046fa300c30 end=try#684d1bdaca93437778609f08a04ce6e7e30a894f mode=check-only

[craterbot]

👌 Experiment pr-58739 created and queued.
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[bors]

⌛ Testing commit cc5088d with merge 3743762f9e7a8307dba17e384bb055948b7fce94...

[bors]

💔 Test failed - checks-travis

[rust-highfive]

The job x86_64-gnu-tools of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[01:29:01] +For more information about this error, try `rustc --explain E0502`.
[01:29:01] +
[01:29:01] 
[01:29:01] The actual stderr differed from the expected stderr.
[01:29:01] Actual stderr saved to /tmp/compiletest6tBQI2/2phase.stderr
[01:29:01] To update references, run this command from build directory:
[01:29:01] tests/run-pass/update-references.sh '/tmp/compiletest6tBQI2' '2phase.rs'
[01:29:01] error: 1 errors occurred comparing output.
[01:29:01] status: exit code: 1
[01:29:01] status: exit code: 1
[01:29:01] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools-bin/miri" "tests/run-pass/2phase.rs" "-L" "/tmp/compiletest6tBQI2" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-C" "prefer-dynamic" "-o" "/tmp/compiletest6tBQI2/2phase.stage-id" "-Dwarnings" "-Dunused" "--edition" "2018" "-L" "/tmp/compiletest6tBQI2/2phase.stage-id.aux" "-A" "unused"
[01:29:01] ------------------------------------------
[01:29:01] 
[01:29:01] ------------------------------------------
[01:29:01] stderr:
[01:29:01] stderr:
[01:29:01] ------------------------------------------
[01:29:01] {"message":"cannot borrow `x` as mutable because it is also borrowed as immutable","code":{"code":"E0502","explanation":"\nThis error indicates that you are trying to borrow a variable as mutable when it\nhas already been borrowed as immutable.\n\nExample of erroneous code:\n\n```compile_fail,E0502\nfn bar(x: &mut i32) {}\nfn foo(a: &mut i32) {\n    let ref y = a; // a is borrowed as immutable.\n    bar(a); // error: cannot borrow `*a` as mutable because `a` is also borrowed\n            //        as immutable\n}\n```\n\nTo fix this error, ensure that you don't have any other references to the\nvariable before trying to access it mutably:\n\n```\nfn bar(x: &mut i32) {}\nfn foo(a: &mut i32) {\n    bar(a);\n    let ref y = a; // ok!\n}\n```\n\nFor more information on the rust ownership system, take a look at\nhttps://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html.\n"},"level":"error","spans":[{"file_name":"tests/run-pass/2phase.rs","byte_start":844,"byte_end":845,"line_start":57,"line_end":57,"column_start":5,"column_end":6,"is_primary":true,"text":[{"text":"    x","highlight_start":5,"highlight_end":6}],"label":"mutable borrow occurs here","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"tests/run-pass/2phase.rs","byte_start":836,"byte_end":838,"line_start":56,"line_end":56,"column_start":13,"column_end":15,"is_primary":false,"text":[{"text":"    let l = &x;","highlight_start":13,"highlight_end":15}],"label":"immutable borrow occurs here","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"tests/run-pass/2phase.rs","byte_start":904,"byte_end":905,"line_start":60,"line_end":60,"column_start":13,"column_end":14,"is_primary":false,"text":[{"text":"            l.set(4);","highlight_start":13,"highlight_end":14}],"label":"immutable borrow later used here","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"error[E0502]: cannot borrow `x` as mutable because it is also borrowed as immutable\n  --> tests/run-pass/2phase.rs:57:5\n   |\n56 |     let l = &x;\n   |             -- immutable borrow occurs here\n57 |     x\n   |     ^ mutable borrow occurs here\n...\n60 |             l.set(4);\n   |             - immutable borrow later used here\n\n"}
[01:29:01] {"message":"For more information about this error, try `rustc --explain E0502`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0502`.\n"}
[01:29:01] 
[01:29:01] ------------------------------------------
[01:29:01] 
---
travis_time:end:1166d5a6:start=1554425823725180590,finish=1554425823731849153,duration=6668563
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:00154c38
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:09eca82e
travis_time:start:09eca82e
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:20d28c16
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[kennytm]

@bors r-

This has changed the UI output of miri's run-pass/2phase.rs test, causing it to degrade from "test-pass" to "test-fail". As the week before beta release, toolstate regression is prohibited. We need to either update miri again or wait until next week.

[pnkfelix]

(i wish I had pushed harder for us to land this code with the lint set to default allow (and then focus on just backporting a change to that lint’s default))

[Centril]

We should not wait a week for this. I would prefer to update miri again. If it comes to it and we cannot, then we should introduce an exception which accepts a breakage specifically for miri.

cc @RalfJung @oli-obk -- hopefully y'all can update miri and we shouldn't have to pick between bad choices...

[Centril]

@bors p=8

[matthewjasper]

@bors r=pnkfelix

[bors]

📌 Commit cc5088d has been approved by pnkfelix

[bors]

⌛ Testing commit cc5088d with merge dec0a98...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: pnkfelix
Pushing dec0a98 to master...

[pnkfelix]

(I'm deliberately not nominating this for beta, due to particularities of how the timing has worked out; it has now landed in nightly, so it will get folded into the beta naturally when the beta-next is cut sometime during the next day or so, and I do not think this change warrants a nomination for beta->stable backport.)