…docs, r=wesleywiser

Update AST validation module docs

Drive-by doc update for AST validation pass:

- Syntax extensions are replaced by proc macros.
- Add rationale for why AST validation pass need to be run
  post-expansion and why the pass is needed in the first place.

This was discussed during this week's [rustc-dev-guide reading club](https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide), and the rationale was explained by cc `@bjorn3.`

…docs, r=wesleywiser

Update AST validation module docs

Drive-by doc update for AST validation pass:

- Syntax extensions are replaced by proc macros.
- Add rationale for why AST validation pass need to be run
  post-expansion and why the pass is needed in the first place.

This was discussed during this week's [rustc-dev-guide reading club](https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide), and the rationale was explained by cc ``@bjorn3.``

…docs, r=wesleywiser

Update AST validation module docs

Drive-by doc update for AST validation pass:

- Syntax extensions are replaced by proc macros.
- Add rationale for why AST validation pass need to be run
  post-expansion and why the pass is needed in the first place.

This was discussed during this week's [rustc-dev-guide reading club](https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide), and the rationale was explained by cc ```@bjorn3.```

…docs, r=wesleywiser

Update AST validation module docs

Drive-by doc update for AST validation pass:

- Syntax extensions are replaced by proc macros.
- Add rationale for why AST validation pass need to be run
  post-expansion and why the pass is needed in the first place.

This was discussed during this week's [rustc-dev-guide reading club](https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide), and the rationale was explained by cc ````@bjorn3.````

…docs, r=wesleywiser

Update AST validation module docs

Drive-by doc update for AST validation pass:

- Syntax extensions are replaced by proc macros.
- Add rationale for why AST validation pass need to be run
  post-expansion and why the pass is needed in the first place.

This was discussed during this week's [rustc-dev-guide reading club](https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide), and the rationale was explained by cc `````@bjorn3.`````

…llaumeGomez

Rollup of 10 pull requests

Successful merges:

 - rust-lang#123714 (Add test for fn pointer duplication.)
 - rust-lang#124091 (Update AST validation module docs)
 - rust-lang#126963 (Add basic Serde serialization capabilities to Stable MIR)
 - rust-lang#127015 (Switch back `non_local_definitions` lint to allow-by-default)
 - rust-lang#127016 (docs: check if the disambiguator matches its suffix)
 - rust-lang#127029 (Fix Markdown tables in platform-support.md)
 - rust-lang#127032 (Enable const casting for `f16` and `f128`)
 - rust-lang#127041 (Migrate `run-make/override-aliased-flags` to `rmake.rs`)
 - rust-lang#127045 (Rename `super_predicates_of` and similar queries to `explicit_*` to note that they're not elaborated)
 - rust-lang#127075 (rustc_data_structures: Explicitly check for 64-bit atomics support)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 11 pull requests

Successful merges:

 - rust-lang#123714 (Add test for fn pointer duplication.)
 - rust-lang#124091 (Update AST validation module docs)
 - rust-lang#127015 (Switch back `non_local_definitions` lint to allow-by-default)
 - rust-lang#127016 (docs: check if the disambiguator matches its suffix)
 - rust-lang#127029 (Fix Markdown tables in platform-support.md)
 - rust-lang#127032 (Enable const casting for `f16` and `f128`)
 - rust-lang#127055 (Mark Hasher::finish as #[must_use])
 - rust-lang#127068 (Stall computing instance for drop shim until it has no unsubstituted const params)
 - rust-lang#127070 (add () to the marker_impls macro for ConstParamTy)
 - rust-lang#127071 (Remove (deprecated & unstable) {to,from}_bits pointer methods)
 - rust-lang#127078 (Enable full tools and profiler for LoongArch Linux targets)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 11 pull requests

Successful merges:

 - rust-lang#123714 (Add test for fn pointer duplication.)
 - rust-lang#124091 (Update AST validation module docs)
 - rust-lang#127015 (Switch back `non_local_definitions` lint to allow-by-default)
 - rust-lang#127016 (docs: check if the disambiguator matches its suffix)
 - rust-lang#127029 (Fix Markdown tables in platform-support.md)
 - rust-lang#127032 (Enable const casting for `f16` and `f128`)
 - rust-lang#127055 (Mark Hasher::finish as #[must_use])
 - rust-lang#127068 (Stall computing instance for drop shim until it has no unsubstituted const params)
 - rust-lang#127070 (add () to the marker_impls macro for ConstParamTy)
 - rust-lang#127071 (Remove (deprecated & unstable) {to,from}_bits pointer methods)
 - rust-lang#127078 (Enable full tools and profiler for LoongArch Linux targets)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 11 pull requests

Successful merges:

 - rust-lang#123714 (Add test for fn pointer duplication.)
 - rust-lang#124091 (Update AST validation module docs)
 - rust-lang#127015 (Switch back `non_local_definitions` lint to allow-by-default)
 - rust-lang#127016 (docs: check if the disambiguator matches its suffix)
 - rust-lang#127029 (Fix Markdown tables in platform-support.md)
 - rust-lang#127032 (Enable const casting for `f16` and `f128`)
 - rust-lang#127055 (Mark Hasher::finish as #[must_use])
 - rust-lang#127068 (Stall computing instance for drop shim until it has no unsubstituted const params)
 - rust-lang#127070 (add () to the marker_impls macro for ConstParamTy)
 - rust-lang#127071 (Remove (deprecated & unstable) {to,from}_bits pointer methods)
 - rust-lang#127078 (Enable full tools and profiler for LoongArch Linux targets)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#124091 - jieyouxu:ast-validation-top-level-docs, r=wesleywiser

Update AST validation module docs

Drive-by doc update for AST validation pass:

- Syntax extensions are replaced by proc macros.
- Add rationale for why AST validation pass need to be run
  post-expansion and why the pass is needed in the first place.

This was discussed during this week's [rustc-dev-guide reading club](https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide), and the rationale was explained by cc ``````@bjorn3.``````