Suggest importable type that differs slightly

[GTimothy]

This PR proposes case insensitive import suggestions.
Previous discussion of this topic here: #72641 and in this PR: #72988
If that is still of interest, a discussion may be needed to limit or expand the included list.
I initially followed the suggestions in #72988.

The tests are based on the tests by @chrissimpkins in #72988.

I added a is_exact_match field to ImportSuggestion to eventually modify the suggestion text accordingly.

Only when no other suggestion is made, do I check for case insensitive import suggestion.

fn test_layout(_x: LayOut){}
//~^ ERROR: cannot find type `LayOut` in this scope

error[E0425]: cannot find type `LayOut` in this scope
  --> $DIR/libstd.rs:3:20
   |
LL | fn test_layout(_x: LayOut){}
   |                    ^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::alloc::Layout;
   |

for a more complex case:
SystemTime exists in the stdlib, but I only suggest case insensitive import when nothing else is suggested

fn test_systemtime(_x: Systemtime){}
//~^ ERROR: cannot find type `Systemtime` in this scope

struct SystemTome{}
mod st{
    struct SystemTame{}
}

error[E0425]: cannot find type `Systemtime` in this scope
  --> $DIR/libstd.rs:428:24
   |
LL | fn test_systemtime(_x: Systemtime){}
   |                        ^^^^^^^^^^
...
LL | struct SystemTome{}
   | ----------------- similarly named struct `SystemTome` defined here
   |
help: a struct with a similar name exists
   |
LL - fn test_systemtime(_x: Systemtime){}
LL + fn test_systemtime(_x: SystemTome){}
   |

During this PR, I ended up adding two other things which could arguably be two separate PRs:

• filtering out typos suggestions that do not have parameters when the typo has some
  motivation: It suggested Clone (no parameter) for the std cloned<(),()> test when I expected Cloned<(),()> to be suggested.

• when suggesting that a missing binding is available in a pattern but not used because behind a .., suggest a MaybeIncorrect fix.
  motivation: this way, I can avoid looking for imports if there is a suggestion.

• custom import message for case insensitive suggestion.

• only suggest case insensitive when no other suggestion is made

• check for enum variant match before suggesting an enum

• check for enum variant parameter requirement before suggesting an enum

• check with reviewers where to place the test, and whether to rename them

• squash and split commits for a clean PR

[GTimothy]

I see from the 247 failed tests that 1-edit difference is too big for small names. 'net' should probably NOT be suggested to replace 'new'...

Edit: i have now switched to case insensitive match only.

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[GTimothy]

upstream change #157991 contains commit cd2d10a and 4f6a600 from #157974 which do some weird file swapping instead of renamings that completely confuses and breaks my rebase attempts.
I may have some skill issue here, does anyone know how to fix this? Is there a proper git workflow to resolve this or do I need to copy my changes over to the swapped file and delete the changes in the original file by hand?

If this is not a skill issue on my part, maybe avoiding this kind of file swapping and splitting this in multiple rename commits would help git not getting confused ?

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rustbot]

⚠️ Warning ⚠️

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  Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtree.
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[rust-log-analyzer]

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

To only update this specific test, also pass `--test-args libstd-case-typo/libstd.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/libstd-case-typo/libstd.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/libstd-case-typo/libstd" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0425]: cannot find type `LayOut` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:3:20
   |
LL | fn test_layout(_x: LayOut){}
   |                    ^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::alloc::Layout;
   |

error[E0425]: cannot find type `system` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:5:20
   |
LL | fn test_system(_x: system){}
   |                    ^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::alloc::System;
   |

error[E0425]: cannot find type `Typeid` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:10:20
   |
LL | fn test_typeid(_x: Typeid){}
   |                    ^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::any::TypeId;
   |

error[E0425]: cannot find type `Escapedefault` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:15:27
   |
LL | fn test_escapedefault(_x: Escapedefault){}
   |                           ^^^^^^^^^^^^^ not found in this scope
   |
help: consider importing one of these similarly named structs
   |
LL + use std::ascii::EscapeDefault;
---

error[E0425]: cannot find type `cell` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:20:18
   |
LL | fn test_cell(_x: cell<()>){}
   |                  ^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::cell::Cell;
   |

error[E0425]: cannot find type `DecodeUTF16` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:25:25
   |
LL | fn test_decodeutf16(_x: DecodeUTF16<()>){}
   |                         ^^^^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::char::DecodeUtf16;
   |

error[E0425]: cannot find type `Escapeunicode` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:28:27
   |
LL | fn test_escapeunicode(_x: Escapeunicode){}
   |                           ^^^^^^^^^^^^^ not found in this scope
   |
help: consider importing one of these similarly named structs
   |
LL + use std::char::EscapeUnicode;
   |
LL + use std::str::EscapeUnicode;
   |

error[E0425]: cannot find type `Tolowercase` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:31:25
   |
LL | fn test_tolowercase(_x: Tolowercase){}
   |                         ^^^^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::char::ToLowercase;
   |

error[E0425]: cannot find type `Touppercase` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:34:25
   |
LL | fn test_touppercase(_x: Touppercase){}
   |                         ^^^^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::char::ToUppercase;
   |

error[E0425]: cannot find type `reverse` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:39:21
   |
LL | fn test_reverse(_x: reverse<()>){}
   |                     ^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::cmp::Reverse;
   |

error[E0425]: cannot find type `BtreeMap` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:44:22
   |
LL | fn test_btreemap(_x: BtreeMap<(), ()>){}
   |                      ^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::BTreeMap;
   |

error[E0425]: cannot find type `BtreeSet` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:46:22
   |
LL | fn test_btreeset(_x: BtreeSet<()>){}
   |                      ^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::BTreeSet;
   |

error[E0425]: cannot find type `Binaryheap` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:48:24
   |
LL | fn test_binaryheap(_x: Binaryheap<()>){}
   |                        ^^^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::BinaryHeap;
   |

error[E0425]: cannot find type `Hashmap` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:50:21
   |
LL | fn test_hashmap(_x: Hashmap<String, ()>){}
   |                     ^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::HashMap;
   |

error[E0425]: cannot find type `Hashset` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:52:21
   |
LL | fn test_hashset(_x: Hashset<()>){}
   |                     ^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::HashSet;
   |

error[E0425]: cannot find type `Linkedlist` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:54:24
   |
LL | fn test_linkedlist(_x: Linkedlist<()>){}
   |                        ^^^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::LinkedList;
   |

error[E0425]: cannot find type `Vecdeque` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:56:22
   |
LL | fn test_vecdeque(_x: Vecdeque<()>){}
   |                      ^^^^^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |
LL + use std::collections::VecDeque;
   |

error[E0425]: cannot find type `args` in this scope
##[error]  --> /checkout/tests/ui/libstd-case-typo/libstd.rs:61:18
   |
LL | fn test_args(_x: args){}
   |                  ^^^^ not found in this scope
   |
help: consider importing this similarly named struct
   |