[WIP] Rollup of three NLL PR's

[pnkfelix]

Rollup of PRs:

• [NLL] Rework checking for borrows conflicting with drops #54509
• add "temporary value borrowed for too long" error #54164
• [NLL] Be more permissive when checking access due to Match #53438

(Includes a couple updates to get them workings as follow-on commits.)

[rust-highfive]

r? @davidtwco

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[pnkfelix]

(marking as [WIP] while I run test bulids atop specific targets like WASM, as demonstrated in cd69fb0.)

[rust-highfive]

The job x86_64-gnu-llvm-5.0 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.

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[00:58:03] failures:
[00:58:03] [00:58:03] ---- [ui (nll)] ui/span/borrowck-ref-into-rvalue.rs stdout ----
[00:58:03] diff of stderr:
[00:58:03] [00:58:03] - error[E0597]: borrowed value does not live long enough
[00:58:03] + error[E0714]: temporary value dropped while borrowed
[00:58:03] 3 |
[00:58:03] 3 |
[00:58:03] 4 LL | match Some("Hello".to_string()) {
[00:58:03] [00:58:03] - | ^^^^^^^^^^^^^^^^^^^^^^^^^ temporary value does not live long enough
[00:58:03] + | ^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
[00:58:03] 6 ...
[00:58:03] 7 LL | }
[00:58:03] - | - temporary value only lives until here
[00:58:03] + | - temporary value is freed at the end of this statement
[00:58:03] 9 LL | println!("{}", *msg);
[00:58:03] 11 |
[00:58:03] [00:58:03] 13 [00:58:03] 14 error: aborting due to previous error
[00:58:03] 14 error: aborting due to previous error
[00:58:03] 15 [00:58:03] - For more information about this error, try `rustc --explain E0597`.
[00:58:03] + For more information about this error, try `rustc --explain E0714`.
[00:58:03] 17 [00:58:03] [00:58:03] [00:58:03] The actual stderr differed from the expected stderr.
[00:58:03] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/span/borrowck-ref-into-rvalue.nll/borrowck-ref-into-rvalue.nll.stderr
[00:58:03] To update references, rerun the tests and pass the `--bless` flag
[00:58:03] To only update this specific test, also pass `--test-args span/borrowck-ref-into-rvalue.rs`
[00:58:03] error: 1 errors occurred comparing output.
[00:58:03] status: exit code: 1
[00:58:03] status: exit code: 1
[00:58:03] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/span/borrowck-ref-into-rvalue.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/span/borrowck-ref-into-rvalue.nll/a" "-Zborrowck=mir" "-Ztwo-phase-borrows" "-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/span/borrowck-ref-into-rvalue.nll/auxiliary" "-A" "unused"
[00:58:03] ------------------------------------------
[00:58:03] [00:58:03] ------------------------------------------
[00:58:03] stderr:
[00:58:03] stderr:
[00:58:03] ------------------------------------------
[00:58:03] {"message":"temporary value dropped while borrowed","code":{"code":"E0714","explanation":"\nThis error indicates that a temporary value is being dropped\nwhile a borrow is still in active use.\n\nErroneous code example:\n\n```compile_fail,E0714\n# #![feature(nll)]\nfn foo() -> i32 { 22 }\nfn bar(x: &i32) -> &i32 { x }\nlet p = bar(&foo());\n // ------ creates a temporary\nlet q = *p;\n```\n\nHere, the expression `&foo()` is borrowing the expression\n`foo()`. As `foo()` is call to a function, and not the name of\na variable, this creates a **temporary** -- that temporary stores\nthe return value from `foo()` so that it can be borrowed.\nSo you might imagine that `let p = bar(&foo())` is equivalent\nto this:\n\n```compile_fail,E0597\n# fn foo() -> i32 { 22 }\n# fn bar(x: &i32) -> &i32 { x }\nlet p = {\n let tmp = foo(); // the temporary\n bar(&tmp)\n}; // <-- tmp is freed as we exit this block\nlet q = p;\n```\n\nWhenever a temporary is created, it is automatically dropped (freed)\naccording to fixed rules. Ordinarily, the temporary is dropped\nat the end of the enclosing statement -- in this case, after the `let`.\nThis is illustrated in the example above by showing that `tmp` would\nbe freed as we exit the block.\n\nTo fix this problem, you need to create a local variable\nto store the value in rather than relying on a temporary.\nFor example, you might change the original program to\nthe following:\n\n```\nfn foo() -> i32 { 22 }\nfn bar(x: &i32) -> &i32 { x }\nlet value = foo(); // dropped at the end of the enclosing block\nlet p = bar(&value);\nlet q = *p;\n```\n\nBy introducing the explicit `let value`, we allocate storage\nthat will last until the end of the enclosing block (when `value`\ngoes out of scope). When we borrow `&value`, we are borrowing a\nlocal variable that already exists, and hence no temporary is created.\n\nTemporaries are not always dropped at the end of the enclosing\nstatement. In simple cases where the `&` expression is immediately\nstored into a variable, the compiler will automatically extend\nthe lifetime of the temporary until the end of the enclosinb\nblock. Therefore, an alternative way to fix the original\nprogram is to write `let tmp = &foo()` and not `let tmp = foo()`:\n\n```\nfn foo() -> i32 { 22 }\nfn bar(x: &i32) -> &i32 { x }\nlet value = &foo();\nlet p = bar(value);\nlet q = *p;\n```\n\nHere, we are still borrowing `foo()`, but as the borrow is assigned\ndirectly into a variable, the temporary will not be dropped until\nthe end of the enclosing block. Similar rules apply when temporaries\nare stored into aggregate structures like a tuple or struct:\n\n```\n// Here, two temporaries are created, but\n// as they are stored directly into `value`,\n// they are not dropped until the end of the\n// enclosing block.\nfn foo() -> i32 { 22 }\nlet value = (&foo(), &foo());\n```\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/span/borrowck-ref-into-rvalue.rs","byte_start":502,"byte_end":527,"line_start":13,"line_end":13,"column_start":11,"column_end":36,"is_primary":true,"text":[{"text":" match Some(\"Hello\".to_string()) {","highlight_start":11,"highlight_end":36}],"label":"creates a temporary which is freed while still in use","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"/checkout/src/test/ui/span/borrowck-ref-into-rvalue.rs","byte_start":680,"byte_end":681,"line_start":19,"line_end":19,"column_start":5,"column_end":6,"is_primary":false,"text":[{"text":" }","highlight_start":5,"highlight_end":6}],"label":"temporary value is freed at the end of this statement","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"/checkout/src/test/ui/span/borrowck-ref-into-rvalue.rs","byte_start":701,"byte_end":705,"line_start":20,"line_end":20,"column_start":20,"column_end":24,"is_primary":false,"text":[{"text":" println!(\"{}\", *msg);","highlight_start":20,"highlight_end":24}],"label":"borrow later used here","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"consider using a `let` binding to create a longer lived value","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0714]: temporary value dropped while borrowed\n --> /checkout/src/test/ui/span/borrowck-ref-into-rvalue.rs:13:11\n |\nLL | match Some(\"Hello\".to_string()) {\n | ^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use\n...\nLL | }\n | - temporary value is freed at the end of this statement\nLL | println!(\"{}\", *msg);\n | ---- borrow later used here\n |\n = note: consider using a `let` binding to create a longer lived value\n\n"}
[00:58:03] {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
[00:58:03] {"message":"For more information about this error, try `rustc --explain E0714`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0714`.\n"}
[00:58:03] ------------------------------------------
[00:58:03] [00:58:03] thread '[ui (nll)] ui/span/borrowck-ref-into-rvalue.rs' panicked at 'explicit panic', tools/compiletest/src/runtest.rs:3238:9
[00:58:03] note: Run with `RUST_BACKTRACE=1` for a backtrace.
---
[00:58:03] [00:58:03] thread 'main' panicked at 'Some tests failed', tools/compiletest/src/main.rs:496:22
[00:58:03] [00:58:03] [00:58:03] 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-5.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options " "--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" "5.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always" "--compare-mode" "nll"
[00:58:03] [00:58:03] [00:58:03] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[00:58:03] Build completed unsuccessfully in 0:13:46
[00:58:03] Build completed unsuccessfully in 0:13:46
[00:58:03] Makefile:58: recipe for target 'check' failed
[00:58:03] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:04c83124
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:12681d38:start=1537808522617549537,finish=1537808522621259350,duration=3709813
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:084a090b
$ 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:180bf48c
travis_time:start:180bf48c
$ 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:0f571afc
$ dmesg | grep -i kill

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[bors]

☔ The latest upstream changes (presumably #54509) made this pull request unmergeable. Please resolve the merge conflicts.

[pnkfelix]

Both #54509 and #53438 landed so this "rollup" does not need to stay open. I'll just focus my attention on getting #54164 landed on its own.