Stabilise irrefutable if-let and while-let patterns

[varkor]

This stabilises RFC 2086 (#44495).

This replaces #55639, as we want to stabilise this in time for the beta cut-off.

Closes #55639.

r? @Centril

[Centril]

@bors r+ p=1

[bors]

📌 Commit afcb938 has been approved by Centril

[rust-highfive]

The job x86_64-gnu-llvm-6.0 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.

travis_time:end:09f4ea60:start=1547262790484177184,finish=1547262792584946636,duration=2100769452
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
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[01:04:59] ....................................i.....................................................F......
[01:04:59] 
[01:04:59] ---- [ui] ui/while-let.rs stdout ----
[01:04:59] diff of stderr:
[01:04:59] 
[01:04:59] 
[01:04:59] 27    |
[01:04:59] 28 LL | /     while let a = 1 { //~ WARN irrefutable while-let
[01:04:59] 29 LL | |         println!("irrefutable pattern");
[01:04:59] + LL | |         break;
[01:04:59] 30 LL | |     }
[01:04:59] 32 
[01:04:59] 
[01:04:59] 
[01:04:59] The actual stderr differed from the expected stderr.
[01:04:59] The actual stderr differed from the expected stderr.
[01:04:59] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/while-let/while-let.stderr
[01:04:59] To update references, rerun the tests and pass the `--bless` flag
[01:04:59] To only update this specific test, also pass `--test-args while-let.rs`
[01:04:59] error: 1 errors occurred comparing output.
[01:04:59] status: exit code: 0
[01:04:59] status: exit code: 0
[01:04:59] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/while-let.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/while-let/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/while-let/auxiliary" "-A" "unused"
[01:04:59] ------------------------------------------
[01:04:59] 
[01:04:59] ------------------------------------------
[01:04:59] stderr:
[01:04:59] stderr:
[01:04:59] ------------------------------------------
[01:04:59] {"message":"irrefutable while-let pattern","code":{"code":"irrefutable_let_patterns","explanation":null},"level":"warning","spans":[{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":103,"byte_end":108,"line_start":6,"line_end":6,"column_start":13,"column_end":18,"is_primary":true,"text":[{"text":"            while let $p = $e $b","highlight_start":13,"highlight_end":18}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":{"span":{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":256,"byte_end":348,"line_start":15,"line_end":17,"column_start":5,"column_end":8,"is_primary":false,"text":[{"text":"    foo!(a, 1, { //~ WARN irrefutable while-let","highlight_start":5,"highlight_end":48},{"text":"        println!(\"irrefutable pattern\");","highlight_start":1,"highlight_end":41},{"text":"    });","highlight_start":1,"highlight_end":8}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null},"macro_decl_name":"foo!","def_site_span":{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":31,"byte_end":140,"line_start":4,"line_end":8,"column_start":5,"column_end":6,"is_primary":false,"text":[{"text":"    macro_rules! foo{","highlight_start":5,"highlight_end":22},{"text":"        ($p:pat, $e:expr, $b:block) => {{","highlight_start":1,"highlight_end":42},{"text":"            while let $p = $e $b","highlight_start":1,"highlight_end":33},{"text":"        }}","highlight_start":1,"highlight_end":11},{"text":"    }","highlight_start":1,"highlight_end":6}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}}}],"children":[{"message":"#[warn(irrefutable_let_patterns)] on by default","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"warning: irrefutable while-let pattern\n  --> /checkout/src/test/ui/while-let.rs:6:13\n   |\nLL |               while let $p = $e $b\n   |               ^^^^^\n...\nLL | /     foo!(a, 1, { //~ WARN irrefutable while-let\nLL | |         println!(\"irrefutable pattern\");\nLL | |     });\n   | |_______- in this macro invocation\n   |\n   = note: #[warn(irrefutable_let_patterns)] on by default\n\n"}
[01:04:59] {"message":"irrefutable while-let pattern","code":{"code":"irrefutable_let_patterns","explanation":null},"level":"warning","spans":[{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":103,"byte_end":108,"line_start":6,"line_end":6,"column_start":13,"column_end":18,"is_primary":true,"text":[{"text":"            while let $p = $e $b","highlight_start":13,"highlight_end":18}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":{"span":{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":217,"byte_end":233,"line_start":11,"line_end":11,"column_start":13,"column_end":29,"is_primary":false,"text":[{"text":"            foo!($p, $e, $b)","highlight_start":13,"highlight_end":29}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":{"span":{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":353,"byte_end":445,"line_start":18,"line_end":20,"column_start":5,"column_end":8,"is_primary":false,"text":[{"text":"    bar!(a, 1, { //~ WARN irrefutable while-let","highlight_start":5,"highlight_end":48},{"text":"        println!(\"irrefutable pattern\");","highlight_start":1,"highlight_end":41},{"text":"    });","highlight_start":1,"highlight_end":8}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null},"macro_decl_name":"bar!","def_site_span":{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":145,"byte_end":250,"line_start":9,"line_end":13,"column_start":5,"column_end":6,"is_primary":false,"text":[{"text":"    macro_rules! bar{","highlight_start":5,"highlight_end":22},{"text":"        ($p:pat, $e:expr, $b:block) => {{","highlight_start":1,"highlight_end":42},{"text":"            foo!($p, $e, $b)","highlight_start":1,"highlight_end":29},{"text":"        }}","highlight_start":1,"highlight_end":11},{"text":"    }","highlight_start":1,"highlight_end":6}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}}},"macro_decl_name":"foo!","def_site_span":{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":31,"byte_end":140,"line_start":4,"line_end":8,"column_start":5,"column_end":6,"is_primary":false,"text":[{"text":"    macro_rules! foo{","highlight_start":5,"highlight_end":22},{"text":"        ($p:pat, $e:expr, $b:block) => {{","highlight_start":1,"highlight_end":42},{"text":"            while let $p = $e $b","highlight_start":1,"highlight_end":33},{"text":"        }}","highlight_start":1,"highlight_end":11},{"text":"    }","highlight_start":1,"highlight_end":6}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}}}],"children":[],"rendered":"warning: irrefutable while-let pattern\n  --> /checkout/src/test/ui/while-let.rs:6:13\n   |\nLL |               while let $p = $e $b\n   |               ^^^^^\n...\nLL | /     bar!(a, 1, { //~ WARN irrefutable while-let\nLL | |         println!(\"irrefutable pattern\");\nLL | |     });\n   | |_______- in this macro invocation\n\n"}
[01:04:59] {"message":"irrefutable while-let pattern","code":{"code":"irrefutable_let_patterns","explanation":null},"level":"warning","spans":[{"file_name":"/checkout/src/test/ui/while-let.rs","byte_start":469,"byte_end":579,"line_start":24,"line_end":27,"column_start":5,"column_end":6,"is_primary":true,"text":[{"text":"    while let a = 1 { //~ WARN irrefutable while-let","highlight_start":5,"highlight_end":53},{"text":"        println!(\"irrefutable pattern\");","highlight_start":1,"highlight_end":41},{"text":"        break;","highlight_start":1,"highlight_end":15},{"text":"    }","highlight_start":1,"highlight_end":6}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"warning: irrefutable while-let pattern\n  --> /checkout/src/test/ui/while-let.rs:24:5\n   |\nLL | /     while let a = 1 { //~ WARN irrefutable while-let\nLL | |         println!(\"irrefutable pattern\");\nLL | |         break;\nLL | |     }\n   | |_____^\n\n"}
[01:04:59] ------------------------------------------
[01:04:59] 
[01:04:59] thread '[ui] ui/while-let.rs' panicked at 'explicit panic', src/tools/compiletest/src/runtest.rs:3245:9
[01:04:59] 
---
[01:04:59] 
[01:04:59] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:495:22
[01:04:59] 
[01:04:59] 
[01:04:59] 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-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -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" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[01:04:59] 
[01:04:59] 
[01:04:59] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:04:59] Build completed unsuccessfully in 0:04:13
[01:04:59] Build completed unsuccessfully in 0:04:13
[01:04:59] Makefile:48: recipe for target 'check' failed
[01:04:59] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0bd49ead
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sat Jan 12 04:18:23 UTC 2019

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[bors]

⌛️ Testing commit afcb938 with merge 854c924...

[Centril]

@bors retry

[Centril]

@bors r-

[Centril]

@bors r+ p=1

[bors]

📌 Commit 0e1402d has been approved by Centril