add more FIXMEs and details to ui/README.md

Author: cyrgani

tests/ui/README.md

@@ -36,6 +36,8 @@ These tests exercise the [`annotate-snippets`]-based emitter implementation.
 
 [`annotate-snippets`]: https://github.com/rust-lang/annotate-snippets-rs
 
+**FIXME**: merge this with `error-emitter`
+
 ## `tests/ui/anon-params`
 
 These tests deal with anonymous parameters (no name, only type), a deprecated feature that becomes a hard error in Edition 2018.
@@ -141,6 +143,8 @@ However, only a single test was ever added to this category: <https://github.com
 
 Tests for pattern binding in match expressions, let statements, and other binding contexts. E.g. binding modes and refutability. See [Patterns | Reference](https://doc.rust-lang.org/reference/patterns.html).
 
+**FIXME**: quite some overlap with `tests/ui/pattern` and `tests/ui/match`.
+
 ## `tests/ui/binop/`: Binary operators
 
 Tests for binary operators (such as `==`, `&&` or `^`). E.g. overloading, type checking, and diagnostics for invalid operations.
@@ -272,7 +276,7 @@ This directory is actually for the standard library [`std::process::Command`](ht
 
 Some traits' implementation must be compared with their definition, checking for problems such as the implementation having stricter requirements (such as needing to implement `Copy`).
 
-This subdirectory is *not* intended comparison traits (`PartialEq`, `Eq`, `PartialOrd`, `Ord`).
+This subdirectory is *not* intended for comparison traits (`PartialEq`, `Eq`, `PartialOrd`, `Ord`).
 
 ## `tests/ui/compile-flags/`
 
@@ -448,6 +452,8 @@ Exercises diagnostics for when a code block attempts to gain ownership of a non-
 
 Exercises diagnostics for disallowed struct destructuring.
 
+**FIXME**: does this really need to be its own immediate subdirectory?
+
 ## `tests/ui/dist`
 
 Tests that require distribution artifacts.
@@ -508,7 +514,7 @@ These tests run in specific Rust editions, such as Rust 2015 or Rust 2018, and c
 
 ## `tests/ui/eii`: Externally Implementable Items
 
-Exercises `eii` keyword.
+Exercises the `#[eii]` attribute and related features.
 
 ## `tests/ui/entry-point/`: `main` function
 
@@ -611,8 +617,6 @@ Tests for `#![feature(fn_traits)]`. See [`fn_traits` | The Unstable book](https:
 
 Anything to do with loops and `for`, `loop` and `while` keywords to express them.
 
-**FIXME**: After `ui/for` is merged into this, also carry over its SUMMARY text.
-
 ## `tests/ui/force-inlining/`: `#[rustc_force_inline]`
 
 Tests for `#[rustc_force_inline]`, which will force a function to always be labelled as inline by the compiler (it will be inserted at the point of its call instead of being used as a normal function call.) If the compiler is unable to inline the function, an error will be reported. See <https://github.com/rust-lang/rust/pull/134082>.
@@ -730,6 +734,8 @@ Tests on type inference.
 
 Tests for diagnostics on infinitely recursive types without indirection.
 
+**FIXME**: check for overlap with `structs-enums/enum-rec` and `structs-enums/struct-rec`
+
 ## `tests/ui/inline-const/`
 
 These tests revolve around the inline `const` block that forces the compiler to const-eval its content.
@@ -853,7 +859,9 @@ Tests exercising analysis for unused variables, unreachable statements, function
 
 ## `tests/ui/loop-match`
 
-Tests for `loop` with `match` expressions.
+Tests for the `loop_match` feature to optimize `loop`s consisting of one big `match` expressions.
+
+See [Tracking issue for way to express intraprocedural finite state machines #132306](https://github.com/rust-lang/rust/issues/132306).
 
 ## `tests/ui/loops/`
 
@@ -891,6 +899,8 @@ See [Tracking issue for allowing overlapping implementations for marker trait #2
 
 Broad category of tests on `match` constructs.
 
+**FIXME**: many tests overlap with `tests/ui/bindings`, try to reduce duplication.
+
 ## `tests/ui/methods/`
 
 A broad category for anything related to methods and method resolution.
@@ -899,6 +909,8 @@ A broad category for anything related to methods and method resolution.
 
 Certain mir-opt regression tests.
 
+**FIXME**: many tests in this directory are not about MIR or optimizations, relocate these.
+
 ## `tests/ui/mir-dataflow`
 
 Tests for MIR dataflow analysis.
@@ -977,6 +989,8 @@ Tests that exercises edge cases, such as specific floats, large or very small nu
 
 Tests that checks numeric types and their interactions, such as casting among them with `as` or providing the wrong numeric suffix.
 
+**FIXME**: these tests could get moved to other directories, in particular `cast/` or `parser/`.
+
 ## `tests/ui/object-lifetime/`
 
 Tests on lifetimes on objects, such as a lifetime bound not being able to be deduced from context, or checking that lifetimes are inherited properly.
@@ -1308,7 +1322,7 @@ Some standard library tests which are too inconvenient or annoying to implement
 
 ## `tests/ui/str/`
 
-Exercise `str` keyword and string slices.
+Exercise `str` primitive and string slices.
 
 ## `tests/ui/structs/`
 
@@ -1464,6 +1478,8 @@ See [RFC 0132 Unified Function Call Syntax](https://github.com/rust-lang/rfcs/bl
 
 `#![feature(unboxed_closures)]`, `Fn`, `FnMut` and `FnOnce` traits
 
+**FIXME**: many tests have `unboxed-closure` in their name but only test normal closures, rename these.
+
 See [Tracking issue for Fn traits (`unboxed_closures` & `fn_traits` feature)](https://github.com/rust-lang/rust/issues/29625).
 
 ## `tests/ui/underscore-lifetime/`: `'_` elided lifetime