buck2: switch to compact_str instead of smartstring

Summary:
Upsides:

- It seems more actively maintained.
  - Note: on Github issues, they have a couple open reports of fuzz failures
    (from their automation) but those are from a branch, not master.
- It doesn't have this frustrating bug: bodil/smartstring#7

Downsides:

- It doesn't convert String to an inlined value in `From`, but we don't
  actually rely on this (we use small strings mostly when working with directories
  where those elements are produced via an iterator of FileName).

Reviewed By: ndmitchell

Differential Revision: D42313656

fbshipit-source-id: 0708866fced3b32941047755b770244287f6ad94

allocative/Cargo.toml

@@ -22,7 +22,7 @@ hashbrown = { version = "0.12.3", optional = true }
 indexmap = { version = "1.9.1", optional = true }
 num-bigint = { version = "0.4.3", optional = true }
 parking_lot = { version = "0.11.2", optional = true }
-smartstring = { version = "0.2.10", optional = true }
+compact_str = { version = "0.6.1", optional = true }
 once_cell = { version = "1.16.0", optional = true }
 owning_ref = { version = "0.4.1", optional = true }
 prost-types = { version = "0.11.2", optional = true }

allocative/src/impls/smartstring.rs → allocative/src/impls/compact_str.rs

@@ -7,21 +7,20 @@
  * of this source tree.
  */
 
-#![cfg(feature = "smartstring")]
+#![cfg(feature = "compact_str")]
 
-use smartstring::SmartString;
-use smartstring::SmartStringMode;
+use compact_str::CompactString;
 
 use crate::allocative_trait::Allocative;
 use crate::impls::common::PTR_NAME;
 use crate::impls::common::UNUSED_CAPACITY_NAME;
 use crate::key::Key;
 use crate::visitor::Visitor;
 
-impl<M: SmartStringMode + 'static> Allocative for SmartString<M> {
+impl Allocative for CompactString {
     fn visit<'a, 'b: 'a>(&self, visitor: &'a mut Visitor<'b>) {
         let mut visitor = visitor.enter_self_sized::<Self>();
-        if !self.is_inline() {
+        if self.is_heap_allocated() {
             let mut visitor = visitor.enter_unique(PTR_NAME, std::mem::size_of::<*const u8>());
             visitor.visit_simple(Key::new("str"), self.len());
             let unused_capacity = self.capacity() - self.len();

allocative/src/impls/mod.rs

@@ -12,6 +12,7 @@
 mod anyhow;
 mod bumpalo;
 pub(crate) mod common;
+mod compact_str;
 mod dashmap;
 mod either;
 mod futures;
@@ -27,6 +28,5 @@ mod prost_types;
 mod relative_path;
 mod sequence_trie;
 mod smallvec;
-mod smartstring;
 mod sorted_vector_map;
 mod std;