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Display information about captured variable in FnMut error #72598

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merged 1 commit into from
Jun 15, 2020

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Aaron1011
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Fixes #69446

When we encounter a region error involving an FnMut closure, we
display a specialized error message. However, we currently do not
tell the user which upvar was captured. This makes it difficult to
determine the cause of the error, especially when the closure is large.

This commit records marks constraints involving closure upvars
with ConstraintCategory::ClosureUpvar. When we decide to 'blame'
a ConstraintCategory::Return, we additionall store
the captured upvar if we found a ConstraintCategory::ClosureUpvar in
the path.

When generating an error message, we point to relevant spans if we have
closure upvar information available. We further customize the message if
an async closure is being returned, to make it clear that the captured
variable is being returned indirectly.

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r? @petrochenkov

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

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 26, 2020
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The job x86_64-gnu-llvm-8 of your PR failed (pretty log, 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.
##[section]Starting: Linux x86_64-gnu-llvm-8
##[section]Starting: Initialize job
Agent name: 'Azure Pipelines 3'
Agent machine name: 'fv-az578'
Current agent version: '2.169.0'
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Version: 20200517.1
Included Software: https://github.com/actions/virtual-environments/blob/ubuntu16/20200517.1/images/linux/Ubuntu1604-README.md
##[endgroup]
Agent running as: 'vsts'
Prepare build directory.
Set build variables.
Download all required tasks.
Download all required tasks.
Downloading task: Bash (3.163.2)
Checking job knob settings.
   Knob: AgentToolsDirectory = /opt/hostedtoolcache Source: ${AGENT_TOOLSDIRECTORY} 
   Knob: AgentPerflog = /home/vsts/perflog Source: ${VSTS_AGENT_PERFLOG} 
Start tracking orphan processes.
##[section]Finishing: Initialize job
##[section]Starting: Configure Job Name
==============================================================================
---
========================== Starting Command Output ===========================
[command]/bin/bash --noprofile --norc /home/vsts/work/_temp/43b454f6-5f41-46ae-ad81-e54be5f161f9.sh

##[section]Finishing: Disable git automatic line ending conversion
##[section]Starting: Checkout rust-lang/rust@refs/pull/72598/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
---
##[command]git remote add origin https://github.com/rust-lang/rust
##[command]git config gc.auto 0
##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
##[command]git config --get-all http.proxy
##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/72598/merge:refs/remotes/pull/72598/merge
---
 ---> cb2676f08729
Step 5/8 : ENV RUST_CONFIGURE_ARGS       --build=x86_64-unknown-linux-gnu       --llvm-root=/usr/lib/llvm-8       --enable-llvm-link-shared       --set rust.thin-lto-import-instr-limit=10
 ---> Using cache
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Step 6/8 : ENV SCRIPT python2.7 ../x.py test --exclude src/tools/tidy &&            python2.7 ../x.py test src/test/mir-opt --pass=build                                   --target=armv5te-unknown-linux-gnueabi &&            python2.7 ../x.py test src/tools/tidy
 ---> 599b9ac96b27
Step 7/8 : ENV NO_DEBUG_ASSERTIONS=1
 ---> Using cache
 ---> 091087e35a36
---
   Compiling fmt_macros v0.0.0 (/checkout/src/libfmt_macros)
   Compiling chalk-rust-ir v0.10.0
   Compiling rustc_ast_pretty v0.0.0 (/checkout/src/librustc_ast_pretty)
   Compiling rustc_hir v0.0.0 (/checkout/src/librustc_hir)
   Compiling rustc_query_system v0.0.0 (/checkout/src/librustc_query_system)
   Compiling chalk-solve v0.10.0
   Compiling rustc_hir_pretty v0.0.0 (/checkout/src/librustc_hir_pretty)
   Compiling rustc_parse v0.0.0 (/checkout/src/librustc_parse)
   Compiling rustc_ast_lowering v0.0.0 (/checkout/src/librustc_ast_lowering)
---
   Compiling fmt_macros v0.0.0 (/checkout/src/libfmt_macros)
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   Compiling rustc_ast_pretty v0.0.0 (/checkout/src/librustc_ast_pretty)
   Compiling rustc_hir v0.0.0 (/checkout/src/librustc_hir)
   Compiling rustc_query_system v0.0.0 (/checkout/src/librustc_query_system)
   Compiling chalk-solve v0.10.0
   Compiling rustc_hir_pretty v0.0.0 (/checkout/src/librustc_hir_pretty)
   Compiling rustc_parse v0.0.0 (/checkout/src/librustc_parse)
   Compiling rustc_ast_lowering v0.0.0 (/checkout/src/librustc_ast_lowering)
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12 LL | |     });
-    | |_____^ returns a reference to a captured variable which escapes the closure body
+    | |_____^ returns an `async` block that contains a reference to a captured variable, which then escapes the closure body
14    |
15    = note: `FnMut` closures only have access to their captured variables while they are executing...
16    = note: ...therefore, they cannot allow references to captured variables to escape

The actual stderr differed from the expected stderr.
Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/async-await/issue-69446-fnmut-capture/issue-69446-fnmut-capture.stderr
Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/async-await/issue-69446-fnmut-capture/issue-69446-fnmut-capture.stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args async-await/issue-69446-fnmut-capture.rs`
error: 1 errors occurred comparing output.
status: exit code: 1
status: exit code: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/async-await/issue-69446-fnmut-capture.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/async-await/issue-69446-fnmut-capture" "-A" "unused" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2018" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/async-await/issue-69446-fnmut-capture/auxiliary"
------------------------------------------

------------------------------------------
stderr:
stderr:
------------------------------------------
error: captured variable cannot escape `FnMut` closure body
  --> /checkout/src/test/ui/async-await/issue-69446-fnmut-capture.rs:19:17
   |
LL |       let mut x = Foo;
   |           ----- variable defined here
LL |       bar(move || async { //~ ERROR captured
   |  _______________-_^
   | |               inferred to be a `FnMut` closure
LL | |         x.foo();
   | |         - variable captured here
LL | |     });
LL | |     });
   | |_____^ returns an `async` block that contains a reference to a captured variable, which then escapes the closure body
   |
   = note: `FnMut` closures only have access to their captured variables while they are executing...
   = note: ...therefore, they cannot allow references to captured variables to escape
error: aborting due to previous error


------------------------------------------
---
thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:348:22
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-8/bin/FileCheck" "--nodejs" "/usr/bin/node" "--host-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "8.0.0" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"


failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test --exclude src/tools/tidy
Build completed unsuccessfully in 1:08:27
Build completed unsuccessfully in 1:08:27
== clock drift check ==
  local time: Tue May 26 03:13:01 UTC 2020
  network time: Tue, 26 May 2020 03:13:01 GMT
== end clock drift check ==

##[error]Bash exited with code '1'.
##[section]Finishing: Run build
##[section]Starting: Checkout rust-lang/rust@refs/pull/72598/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
Author       : Microsoft
Help         : [More Information](https://go.microsoft.com/fwlink/?LinkId=798199)
==============================================================================
Cleaning any cached credential from repository: rust-lang/rust (GitHub)
##[section]Finishing: Checkout rust-lang/rust@refs/pull/72598/merge to s
Cleaning up task key
Start cleaning up orphan processes.
Terminate orphan process: pid (3947) (python)
##[section]Finishing: Finalize Job

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 @rust-lang/infra. (Feature Requests)

Fixes rust-lang#69446

When we encounter a region error involving an `FnMut` closure, we
display a specialized error message. However, we currently do not
tell the user which upvar was captured. This makes it difficult to
determine the cause of the error, especially when the closure is large.

This commit records marks constraints involving closure upvars
with `ConstraintCategory::ClosureUpvar`. When we decide to 'blame'
a `ConstraintCategory::Return`, we additionall store
the captured upvar if we found a `ConstraintCategory::ClosureUpvar` in
the path.

When generating an error message, we point to relevant spans if we have
closure upvar information available. We further customize the message if
an `async` closure is being returned, to make it clear that the captured
variable is being returned indirectly.
@petrochenkov
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r? @RalfJung (because MIR, and because you don't have many assigned PRs compared to other relevant people)

@RalfJung
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I know MIR the way it looks when Miri sees it... but I have never seen any of the code touched by this PR before, sorry. The borrow checker is foreign territory for me. I don't think I can help here.

@Aaron1011
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r? @nikomatsakis for review or reassignment

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based on a quick read, the code looks ok, but I'm curious about some of the diagnostics

@Elinvynia Elinvynia added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 10, 2020
@Aaron1011
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@nikomatsakis: I've responded to all of your comments.

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@bors r+

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bors commented Jun 12, 2020

📌 Commit 9cee22c has been approved by nikomatsakis

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 12, 2020
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Jun 13, 2020
…n, r=nikomatsakis

Display information about captured variable in `FnMut` error

Fixes rust-lang#69446

When we encounter a region error involving an `FnMut` closure, we
display a specialized error message. However, we currently do not
tell the user which upvar was captured. This makes it difficult to
determine the cause of the error, especially when the closure is large.

This commit records marks constraints involving closure upvars
with `ConstraintCategory::ClosureUpvar`. When we decide to 'blame'
a `ConstraintCategory::Return`, we additionall store
the captured upvar if we found a `ConstraintCategory::ClosureUpvar` in
the path.

When generating an error message, we point to relevant spans if we have
closure upvar information available. We further customize the message if
an `async` closure is being returned, to make it clear that the captured
variable is being returned indirectly.
RalfJung added a commit to RalfJung/rust that referenced this pull request Jun 13, 2020
…n, r=nikomatsakis

Display information about captured variable in `FnMut` error

Fixes rust-lang#69446

When we encounter a region error involving an `FnMut` closure, we
display a specialized error message. However, we currently do not
tell the user which upvar was captured. This makes it difficult to
determine the cause of the error, especially when the closure is large.

This commit records marks constraints involving closure upvars
with `ConstraintCategory::ClosureUpvar`. When we decide to 'blame'
a `ConstraintCategory::Return`, we additionall store
the captured upvar if we found a `ConstraintCategory::ClosureUpvar` in
the path.

When generating an error message, we point to relevant spans if we have
closure upvar information available. We further customize the message if
an `async` closure is being returned, to make it clear that the captured
variable is being returned indirectly.
RalfJung added a commit to RalfJung/rust that referenced this pull request Jun 13, 2020
…n, r=nikomatsakis

Display information about captured variable in `FnMut` error

Fixes rust-lang#69446

When we encounter a region error involving an `FnMut` closure, we
display a specialized error message. However, we currently do not
tell the user which upvar was captured. This makes it difficult to
determine the cause of the error, especially when the closure is large.

This commit records marks constraints involving closure upvars
with `ConstraintCategory::ClosureUpvar`. When we decide to 'blame'
a `ConstraintCategory::Return`, we additionall store
the captured upvar if we found a `ConstraintCategory::ClosureUpvar` in
the path.

When generating an error message, we point to relevant spans if we have
closure upvar information available. We further customize the message if
an `async` closure is being returned, to make it clear that the captured
variable is being returned indirectly.
RalfJung added a commit to RalfJung/rust that referenced this pull request Jun 13, 2020
…n, r=nikomatsakis

Display information about captured variable in `FnMut` error

Fixes rust-lang#69446

When we encounter a region error involving an `FnMut` closure, we
display a specialized error message. However, we currently do not
tell the user which upvar was captured. This makes it difficult to
determine the cause of the error, especially when the closure is large.

This commit records marks constraints involving closure upvars
with `ConstraintCategory::ClosureUpvar`. When we decide to 'blame'
a `ConstraintCategory::Return`, we additionall store
the captured upvar if we found a `ConstraintCategory::ClosureUpvar` in
the path.

When generating an error message, we point to relevant spans if we have
closure upvar information available. We further customize the message if
an `async` closure is being returned, to make it clear that the captured
variable is being returned indirectly.
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 15, 2020
Rollup of 10 pull requests

Successful merges:

 - rust-lang#71824 (Check for live drops in constants after drop elaboration)
 - rust-lang#72389 (Explain move errors that occur due to method calls involving `self`)
 - rust-lang#72556 (Fix trait alias inherent impl resolution)
 - rust-lang#72584 (Stabilize vec::Drain::as_slice)
 - rust-lang#72598 (Display information about captured variable in `FnMut` error)
 - rust-lang#73336 (Group `Pattern::strip_*` method together)
 - rust-lang#73341 (_match.rs: fix module doc comment)
 - rust-lang#73342 (Fix iterator copied() documentation example code)
 - rust-lang#73351 (Update E0446.md)
 - rust-lang#73353 (structural_match: non-structural-match ty closures)

Failed merges:

r? @ghost
@bors bors merged commit 5193c5d into rust-lang:master Jun 15, 2020
ecstatic-morse added a commit to ecstatic-morse/rust that referenced this pull request Jun 18, 2020
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Which captured variable cannot escape FnMut closure body?
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