Performance: Use SmallVec in rustfix

[deeprobin]

I suggest using SmallVec (smallvec crate) instead of a regular Vec to improve performance, by having a SmallVec allocate primarily on the stack and the heap is secondary.

Where this could be useful

• rustfix/src/lib.rs

  Lines 28 to 29 in ae9b645

  	) -> serde_json::error::Result<Vec<Suggestion>> {
  	let mut result = Vec::new();

• rustfix/src/lib.rs

  Lines 65 to 66 in ae9b645

  	pub snippets: Vec<Snippet>,
  	pub solutions: Vec<Solution>,

• rustfix/src/lib.rs

  Line 72 in ae9b645

  pub replacements: Vec<Replacement>,

• rustfix/src/replace.rs

  Lines 33 to 34 in ae9b645

  	original: Vec<u8>,
  	parts: Vec<Span>,

• rustfix/src/lib.rs

  Line 107 in ae9b645

  let text_slice = span.text[0].text.chars().collect::<Vec<char>>();

• rustfix/src/lib.rs

  Line 131 in ae9b645

  let last_slice = last.text.chars().collect::<Vec<char>>();

• rustfix/src/lib.rs

  Line 191 in ae9b645

  let solutions: Vec<_> = diagnostic

• rustfix/src/replace.rs

  Line 163 in ae9b645

  let mut new_parts = Vec::with_capacity(self.parts.len() + 2);

Of course, it doesn't make sense to blindly replace something like that, but you could analyze this with benchmarks to see where a SmallVec would make sense.

Additional/useful resources

• Reddit: Improving SmallVec's speed by 60% and why that shouldn't matter to you
• Benchmarking with criterion
• Profiling with perf

[ehuss]

I'm going to close as I don't think performance has been much of a concern.