6a87289fa4
Extend Printer::buf on demand.
So that 55 entries (at 48 bytes each) don't need to be eagerly
initialized on creation.
This speeds up numerous rust-perf benchmark runs, by up to 3%.
```
crates.io-check
avg: -2.4% min: -3.7% max: -1.1%
encoding-check
avg: -2.1% min: -2.9% max: -1.2%
crates.io-opt
avg: -1.3% min: -2.7% max: -0.1%
crates.io
avg: -1.4% min: -2.7% max: -0.3%
encoding-opt
avg: -1.1% min: -2.5% max: 0.1%
encoding
avg: -1.3% min: -2.4% max: -0.3%
hyper-check
avg: -1.7% min: -2.3% max: -0.9%
regex-check
avg: -1.5% min: -1.9% max: -0.7%
piston-image-check
avg: -0.9% min: -1.8% max: -0.5%
hyper
avg: -1.0% min: -1.7% max: -0.3%
hyper-opt
avg: -0.9% min: -1.7% max: -0.1%
syn-check
avg: -1.0% min: -1.5% max: -0.6%
clap-rs
avg: -0.3% min: -1.5% max: 0.2%
regex-opt
avg: -0.6% min: -1.5% max: -0.0%
regression-31157-check
avg: -1.1% min: -1.4% max: -0.7%
regex
avg: -0.7% min: -1.3% max: -0.1%
clap-rs-check
avg: -0.5% min: -1.2% max: 0.1%
syn-opt
avg: -0.5% min: -1.1% max: -0.1%
syn
avg: -0.5% min: -1.1% max: -0.2%
serde-opt
avg: -0.3% min: -1.1% max: 0.1%
piston-image-opt
avg: -0.4% min: -1.1% max: -0.0%
piston-image
avg: -0.4% min: -1.0% max: -0.0%
```
The syntax crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.
For more information about how these things work in rustc, see the rustc guide: