Rewrite and refactor format_args!() builtin macro.
This is a near complete rewrite of `compiler/rustc_builtin_macros/src/format.rs`.
This gets rid of the massive unmaintanable [`Context` struct](76531befc4/compiler/rustc_builtin_macros/src/format.rs (L176-L263)), and splits the macro expansion into three parts:
1. First, `parse_args` will parse the `(literal, arg, arg, name=arg, name=arg)` syntax, but doesn't parse the template (the literal) itself.
2. Second, `make_format_args` will parse the template, the format options, resolve argument references, produce diagnostics, and turn the whole thing into a `FormatArgs` structure.
3. Finally, `expand_parsed_format_args` will turn that `FormatArgs` structure into the expression that the macro expands to.
In other words, the `format_args` builtin macro used to be a hard-to-maintain 'single pass compiler', which I've split into a three phase compiler with a parser/tokenizer (step 1), semantic analysis (step 2), and backend (step 3). (It's compilers all the way down. ^^)
This can serve as a great starting point for https://github.com/rust-lang/rust/issues/99012, which will only need to change the implementation of 3, while leaving step 1 and 2 unchanged.
It also makes https://github.com/rust-lang/compiler-team/issues/541 easier, which could then upgrade the new `FormatArgs` struct to an `ast` node and remove step 3, moving that step to later in the compilation process.
It also fixes a few diagnostics bugs.
This also [significantly reduces](https://gist.github.com/m-ou-se/b67b2d54172c4837a5ab1b26fa3e5284) the amount of generated code for cases with arguments in non-default order without formatting options, like `"{1} {0}"` or `"{a} {}"`, etc.
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Containment
This affected layout a little and required adjustments to the CSS to
keep spacing the same. In particular, the margins of adjacent items
usually overlap with each other. However, when an item has contain:
layout, any margins of child nodes push out the size of the item itself.
This was making spacing between items a little too big. To solve that, I
removed margins in some places: in particular for certain classes that
often occur at the end of a `details.rustdoc-toggle` block, I removed
their bottom margin. Generally, the margins provided by the next item
down are sufficient.
Also remove an unnecessary margin-top on .code-header.
macros: diagnostic derive on enums
Part of #100717.
Extends `#[derive(Diagnostic)]` to work on enums too where each variant acts like a distinct diagnostic - being able to represent diagnostics this way can be quite a bit simpler for some parts of the compiler.
r? `@compiler-errors`
cc `@Xiretza`
Allow more `!Copy` impls
You can already implement `!Copy` for a lot of types (with `#![feature(negative_impls)]`). However, before this PR you could not implement `!Copy` for ADTs whose fields don't implement `Copy` which didn't make any sense. Further, you couldn't implement `!Copy` for types impl'ing `Drop` (equally nonsensical).
``@rustbot`` label T-types F-negative_impls
Fixes#101836.
r? types
