Remove SmallStr and recommend Cow<str>

components/datetime/src/skeleton/reference.rs

@@ -24,6 +24,7 @@ use smallvec::SmallVec;
 /// The `Field`s are only sorted in the [`Skeleton`] in order to provide a deterministic
 /// serialization strategy, and to provide a faster [`Skeleton`] matching operation.
 #[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd)]
+// TODO(#876): Use ZeroVec instead of SmallVec
 pub struct Skeleton(pub(crate) SmallVec<[fields::Field; 5]>);
 
 impl Skeleton {

docs/process/style_guide.md

@@ -634,18 +634,14 @@ In addition to supporting zero-copy deserialization, data structs should also su
 
 ### Conventions for strings in structs :: suggested
 
-Main issue: [#113](https://github.com/unicode-org/icu4x/issues/113)
+Main issue: [#113](https://github.com/unicode-org/icu4x/issues/113), [#571](https://github.com/unicode-org/icu4x/issues/571)
 
-When structs with public string fields contain strings, use the following type conventions:
+When structs with public fields contain strings, use the following type conventions:
 
-- `&'data str` if the struct does not need to own the string.
-- `Cow<'data, str>`  if the string could be borrowed or owned.
+- `Cow<'data, str>` for data provider structs (those with `'data`).
+- `String` for source data structs (with no lifetime).
+- `&str` if the struct does not need to own the string.
 - [TinyStr](https://github.com/zbraniecki/tinystr) if the string is ASCII-only.
-- [SmallString](https://crates.io/crates/smallstr) for shorter strings, with a stack size ∈ {8, 12, 16, 20} that fits a large majority of cases.
-
-For `SmallString`, when determining what constitutes a "large majority of cases", consider 99% as a rule of thumb. If in doubt, start with `Cow<'data, str>`; `SmallString` is an additional optimization when the strings are almost always short.  Another advantage of `SmallString` is the lack of a lifetime parameter.  The stack sizes of 8, 12, 16, and 20 for `SmallString` were chosen because these are the sizes that cause SmallString to have a round number of 32-bit-aligned stack bytes.
-
-In general, use `Cow<'data, str>` instead of `String` in structs if the struct can often use zero-cost construction. Use `String` if the struct always owns its data, such as when the string is always dynamically generated at runtime, or if a lifetime parameter cannot be used ergonomically.
 
 ### Pre-validation of options :: suggested