692: [WIP] Correctly parse attributes r=matklad a=DJMcNab
Reference - https://doc.rust-lang.org/reference/attributes.html
This fixes/investigates inner attributes for:
- [x] `impl` blocks
- [x] `extern` blocks
- [x] `fn`s (fixes#689)
- [x] `mod`s (already supported)
- [x] 'block expressions' (the long text just describes all 'blocks' used as statements)
This also investigates/fixes outer attributes for:
- [ ] 'most statements' (see also: #685, https://doc.rust-lang.org/reference/expressions.html#expression-attributes)
- [x] Enum variants, Struct and Union fields (Fixed in #507)
- [ ] 'Match expression arms' (@matklad can you provide a test case which explains what this means?)
- [ ] 'Generic lifetime or type parameters'
- [ ] 'Elements of array expressions, tuple expressions, call expressions, tuple-style struct and enum variant expressions'
- [ ] 'The tail expression of block expressions'
Co-authored-by: DJMcNab <36049421+djmcnab@users.noreply.github.com>
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