Remove kstring in favor of BString (GitoxideLabs#1460)

Let's not trade safety for some convenience.

This reduces performance by 5% at least (in the WebKit repository at 886077e077a496a6e398df52a4b7915d8cd68f76):

```
❯ hyperfine  "/Users/byron/dev/github.com/Byron/gitoxide/target/release/gix index entries ':(attr:export-ignore)' -i" "gix index entries ':(attr:export-ignore)' -i"
Benchmark 1: /Users/byron/dev/github.com/Byron/gitoxide/target/release/gix index entries ':(attr:export-ignore)' -i
  Time (mean ± σ):     820.1 ms ±  71.7 ms    [User: 759.9 ms, System: 85.9 ms]
  Range (min … max):   778.8 ms … 984.3 ms    10 runs

  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet system without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.

Benchmark 2: gix index entries ':(attr:export-ignore)' -i
  Time (mean ± σ):     782.1 ms ±   1.8 ms    [User: 760.1 ms, System: 43.2 ms]
  Range (min … max):   780.0 ms … 786.0 ms    10 runs

Summary
  gix index entries ':(attr:export-ignore)' -i ran
    1.05 ± 0.09 times faster than /Users/byron/dev/github.com/Byron/gitoxide/target/release/gix index entries ':(attr:export-ignore)' -i
```

gix-attributes/src/lib.rs

@@ -6,7 +6,8 @@
     doc = ::document_features::document_features!()
 )]
 #![cfg_attr(all(doc, feature = "document-features"), feature(doc_cfg, doc_auto_cfg))]
-#![deny(missing_docs, rust_2018_idioms, unsafe_code)]
+#![deny(missing_docs, rust_2018_idioms)]
+#![forbid(unsafe_code)]
 
 pub use gix_glob as glob;
 use kstring::{KString, KStringRef};

gix-attributes/src/name.rs

@@ -1,8 +1,7 @@
+use crate::{Name, NameRef};
 use bstr::{BStr, BString, ByteSlice};
 use kstring::KStringRef;
 
-use crate::{Name, NameRef};
-
 impl<'a> NameRef<'a> {
     /// Turn this ref into its owned counterpart.
     pub fn to_owned(self) -> Name {

gix-attributes/src/parse.rs

@@ -1,10 +1,9 @@
 use std::borrow::Cow;
 
+use crate::{name, AssignmentRef, Name, NameRef, StateRef};
 use bstr::{BStr, ByteSlice};
 use kstring::KStringRef;
 
-use crate::{name, AssignmentRef, Name, NameRef, StateRef};
-
 /// The kind of attribute that was parsed.
 #[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]

gix-attributes/src/search/mod.rs

@@ -1,7 +1,6 @@
-use std::collections::HashMap;
-
 use kstring::KString;
 use smallvec::SmallVec;
+use std::collections::HashMap;
 
 use crate::{Assignment, AssignmentRef};
 

gix-attributes/src/state.rs

@@ -1,29 +1,24 @@
-use bstr::{BStr, ByteSlice};
-use kstring::{KString, KStringRef};
-
 use crate::{State, StateRef};
+use bstr::{BStr, BString, ByteSlice};
 
 /// A container to encapsulate a tightly packed and typically unallocated byte value that isn't necessarily UTF8 encoded.
 #[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-pub struct Value(KString);
+// TODO: This should be some sort of 'smallbstring' - but can't use `kstring` here due to UTF8 requirement. 5% performance boost possible.
+//       What's really needed here is a representation that displays as string when serialized which helps with JSON.
+//       Maybe `smallvec` with display and serialization wrapper would do the trick?
+pub struct Value(BString);
 
 /// A reference container to encapsulate a tightly packed and typically unallocated byte value that isn't necessarily UTF8 encoded.
 #[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-pub struct ValueRef<'a>(#[cfg_attr(feature = "serde", serde(borrow))] KStringRef<'a>);
+pub struct ValueRef<'a>(#[cfg_attr(feature = "serde", serde(borrow))] &'a [u8]);
 
 /// Lifecycle
 impl<'a> ValueRef<'a> {
     /// Keep `input` as our value.
     pub fn from_bytes(input: &'a [u8]) -> Self {
-        Self(KStringRef::from_ref(
-            // SAFETY: our API makes accessing that value as `str` impossible, so illformed UTF8 is never exposed as such.
-            #[allow(unsafe_code)]
-            unsafe {
-                std::str::from_utf8_unchecked(input)
-            },
-        ))
+        Self(input)
     }
 }
 
@@ -42,7 +37,7 @@ impl ValueRef<'_> {
 
 impl<'a> From<&'a str> for ValueRef<'a> {
     fn from(v: &'a str) -> Self {
-        ValueRef(v.into())
+        ValueRef(v.as_bytes().into())
     }
 }
 
@@ -54,7 +49,7 @@ impl<'a> From<ValueRef<'a>> for Value {
 
 impl From<&str> for Value {
     fn from(v: &str) -> Self {
-        Value(KString::from_ref(v))
+        Value(v.as_bytes().into())
     }
 }
 

gix-attributes/tests/parse/mod.rs

@@ -1,4 +1,5 @@
 use bstr::BString;
+use gix_attributes::state::ValueRef;
 use gix_attributes::{parse, StateRef};
 use gix_glob::pattern::Mode;
 use gix_testtools::fixture_bytes;
@@ -275,6 +276,19 @@ fn attributes_can_have_values() {
     );
 }
 
+#[test]
+fn attributes_can_have_illformed_utf8() {
+    assert_eq!(
+        byte_line(b"p a=one b=\xC3\x28\x41 c=d "),
+        (
+            pattern("p", Mode::NO_SUB_DIR, None),
+            vec![value("a", "one"), byte_value("b", b"\xC3\x28\x41"), value("c", "d")],
+            1
+        ),
+        "illformed UTF8 is fully supported"
+    );
+}
+
 #[test]
 fn attributes_see_state_adjustments_over_value_assignments() {
     assert_eq!(
@@ -325,6 +339,10 @@ fn value<'b>(attr: &str, value: &'b str) -> (BString, StateRef<'b>) {
     (attr.into(), StateRef::Value(value.into()))
 }
 
+fn byte_value<'b>(attr: &str, value: &'b [u8]) -> (BString, StateRef<'b>) {
+    (attr.into(), StateRef::Value(ValueRef::from_bytes(value)))
+}
+
 fn pattern(name: &str, flags: gix_glob::pattern::Mode, first_wildcard_pos: Option<usize>) -> parse::Kind {
     parse::Kind::Pattern(gix_glob::Pattern {
         text: name.into(),
@@ -344,6 +362,17 @@ fn line(input: &str) -> ExpandedAttribute {
     try_line(input).unwrap()
 }
 
+fn byte_line(input: &[u8]) -> ExpandedAttribute {
+    try_byte_line(input).unwrap()
+}
+
+fn try_byte_line(input: &[u8]) -> Result<ExpandedAttribute, parse::Error> {
+    let mut lines = gix_attributes::parse(input);
+    let res = expand(lines.next().unwrap())?;
+    assert!(lines.next().is_none(), "expected only one line");
+    Ok(res)
+}
+
 fn lenient_lines(input: &str) -> Vec<ExpandedAttribute> {
     gix_attributes::parse(input.as_bytes())
         .map(expand)

gix-attributes/tests/search/mod.rs

@@ -270,7 +270,7 @@ fn given_attributes_are_made_available_in_given_order() -> crate::Result {
 fn size_of_outcome() {
     assert_eq!(
         std::mem::size_of::<Outcome>(),
-        904,
+        840,
         "it's quite big, shouldn't change without us noticing"
     )
 }