remove notion of Implicit derefs from mem-cat

[nikomatsakis]

PointerKind is included in LoanPath and hence forms part of the equality check; this led to having two unequal paths that both represent *x, depending on whether the * was inserted automatically or explicitly. Bad mojo.

Fixes #51117

r? @eddyb

[nikomatsakis]

(Travis will probably fail; I'm still running ./x.py test locally)

[eddyb]

r=me with tests fixed

[rust-highfive]

The job x86_64-gnu-llvm-3.9 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:start:test_ui
Check compiletest suite=ui mode=ui (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[00:40:33] 
[00:40:33] running 1479 tests
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nformation about this error, try `rustc --explain E0499`.
[00:41:38] 
[00:41:38] 
[00:41:38] 
[00:41:38] The actual stderr differed from the expected stderr.
[00:41:38] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/borrowck/issue-51117/issue-51117.stderr
[00:41:38] To update references, rerun the tests and pass the `--bless` flag
[00:41:38] To only update this specific test, also pass `--test-args borrowck/issue-51117.rs`
[00:41:38] error: 1 errors occurred comparing output.
[00:41:38] status: exit code: 101
[00:41:38] status: exit code: 101
[00:41:38] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/borrowck/issue-51117.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/borrowck/issue-51117/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/borrowck/issue-51117/auxiliary" "-A" "unused"
[00:41:38] ------------------------------------------
[00:41:38] 
[00:41:38] ------------------------------------------
[00:41:38] stderr:
[00:41:38] stderr:
[00:41:38] ------------------------------------------
[00:41:38] {"message":"cannot borrow `*bar` as mutable more than once at a time","code":{"code":"E0499","explanation":"\nA variable was borrowed as mutable more than once. Erroneous code example:\n\n```compile_fail,E0499\nlet mut i = 0;\nlet mut x = &mut i;\nlet mut a = &mut i;\n// error: cannot borrow `i` as mutable more than oncee\n  --> /checkout/src/test/ui/borrowck/issue-51117.rs:20:13\n   |\nLL |         Some(baz) => {\n   |              --- first mutable borrow occurs here\nLL |             bar.take(); //~ ERROR cannot borrow\n   |             ^^^ second mutable borrow occurs here\n...\nLL |     }\n   |     - first borrow ends here\n\n"}
[00:41:38] {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
[00:41:38] {"message":"For more information about this error, try `rustc --explain E0499`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0499`.\n"}
[00:41:38] ------------------------------------------
[00:41:38] 
[00:41:38] thread '[ui] ui/borrowck/issue-51117.rs' panicked at 'explicit panic', tools/compiletest/src/runtest.rs:3053:9
[00:41:38] note: Run with `RUST_BACKTRACE=1` for a backtrace.
---
[00:41:38] - error[E0507]: cannot move out of indexed content
[00:41:38] + error[E0507]: cannot move out of borrowed content
[00:41:38] 2   --> $DIR/issue-40402-1.rs:19:13
[00:41:38] 3    |
[00:41:38] 4 LL |     let e = f.v[0]; //~ ERROR cannot move out of indexed content
[00:41:38] 5    |             ^^^^^^
[00:41:38] 6    |             |
[00:41:38] -    |             cannot move out of indexed content
[00:41:38] +    |             cannot move out of borrowed content
[00:41:38] +    |             cannot move out of borrowed content
[00:41:38] 8    |             help: consider using38] {"message":"cannot move out of borrowed content","code":{"code":"E0507","explanation":"\nYou tried to move out of a value which was borrowed. Erroneous code example:\n\n```compile_fail,E0507\nuse std::cell::RefCell;\n\nstruct TheDarkKnight;\n\nimpl TheDarkKnight {\n    fn nothing_is_true(self) {}\n}\n\nfn main() {\n    let x = RefCell::new(TheDarkKnight);\n\n    x.borrow().nothing_is_true(); // error: cannot move out of borrowed content\n}\n```\n\nHere, the `nothing_is_true` method takes the ownership of `self`. However,\n`self` cannot be moved because `.borrow()` only provides an `&TheDarkKnight`,\nwhich is a borrow of the content owned by the `RefCell`. To fix this error,\nyou have three choices:\n\n* Try to avoid moving the variable.\n* Somehow reclaim the ownership.\n* Implement the `Copy` trait on the type.\n\nExamples:\n\n```\nuse std::cell::RefCell;\n\nstruct TheDarkKnight;\n\nimpl TheDarkKnight {\n    fn nothing_is_true(&self) {} // First case, we don't take ownership\n}\n\nfn main() {\n    let x = RefCell::new(TheDarkKnight);\n\n    x.borrow().nothing_is_true(); // ok!\n}\n```\n\nOr:\n\n```\nuse std::cell::RefCell;\n\nstruct TheDarkKnight;\n\nimpl TheDarkKnight {\n    fn nothing_is_true(self) {}\n}\n\nfn main() {\n    let x = RefCell::new(TheDarkKnight);\n    let x = x.into_inner(); // we get back ownership\n\n    x.nothing_is_true(); // ok!\n}\n```\n\nOr:\n\n```\nuse std::cell::RefCell;\n\n#[derive(Clone, Copy)] // we implement the Copy trait\nstruct TheDarkKnight;\n\nimpl TheDarkKnight {\n    fn nothing_is_true(self) {}\n}\n\nfn main() {\n    let x = RefCell::new(TheDarkKnight);\n\n    x.borrow().nothing_is_true(); // ok!\n}\n```\n\nMoving a member out of a mutably borrowed struct will also cause E0507 error:\n\n```compile_fail,E0507\nstruct TheDarkKnight;\n\nimpl TheDarkKnight {\n    fn nothing_is_true(self) {}\n}\n\nstruct Batcave {\n    knight: TheDarkKnight\n}\n\nfn main() {\n    let mut cave = Batcave {\n        knight: TheDarkKnight\n    };\n    let borrowed = &mut cave;\n\n    borrowed.knight.nothing_is_true(); // E0507\n}\n```\n\nIt is fine only if you put something back. `mem::replace` can be used for that:\n\n```\n# struct TheDarkKnight;\n# impl TheDarkKnight { fn nothing_is_true(self) {} }\n# struct Batcave { knight: TheDarkKnight }\nuse std::mem;\n\nlet mut cave = Batcave {\n    knight: TheDarkKnight\n};\nlet borrowed = &mut cave;\n\nmem::replace(&mut borrowed.knight, TheDarkKnight).nothing_is_true(); // ok!\n```\n\nYou can find more information about borrowing in the rust-book:\nhttp://doc.rust-lang.org/book/first-edition/references-and-borrowing.html\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/issue-40402-ref-hints/issue-40402-2.rs","byte_start":646,"byte_end":650,"line_start":15,"line_end":15,"column_start":18,"column_end":22,"is_primary":true,"text":[{"text":"    let (a, b) = x[0]; //~ ERROR cannot move out of indexed content","highlight_start":18,"highlight_end":22}],"label":"cannot move out of borrowed content","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"/checkout/src/test/ui/issue-40402-ref-hints/issue-40402-2.rs","byte_start":638,"byte_end":639,"line_start":15,"line_end":15,"column_start":10,"column_end":11,"is_primary":false,"text":[{"text":"730863262pt
103748 ./obj/build/bootstrap/debug/incremental/bootstrap-c730863262pt/s-f1j8x40deq-1x8944c-34q164wx8plum
103288 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu
103284 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu/release
99904 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu/release/deps
90816 ./obj/build/x86_64-unknown-linux-gnu/stage1

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)

[nikomatsakis]

@eddyb I tweaked the approach somewhat to avoid impacting diagnostics. Maybe you want to re-review? Same basic idea.

[eddyb]

hax!

[nikomatsakis]

Indeed...though I thought it was sort of beautiful in its own way :)

[eddyb]

@bors r+ p=10

[bors]

📌 Commit 8a624b7 has been approved by eddyb

[bors]

⌛ Testing commit 8a624b7 with merge 6de4ec6...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing 6de4ec6 to master...