smol strings

3 files changed, 65 insertions, 3 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 0ae8082f1..91b0c9c55 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -35,6 +35,7 @@ mod grammar;
 mod parser_impl;
 
 mod syntax_kinds;
+mod smol_str;
 mod yellow;
 /// Utilities for simple uses of the parser.
 pub mod utils;
diff --git a/src/smol_str.rs b/src/smol_str.rs
new file mode 100644
index 000000000..2a330c343
--- /dev/null
+++ b/src/smol_str.rs
@@ -0,0 +1,60 @@
+use std::{sync::Arc};
+
+const INLINE_CAP: usize = 22;
+
+#[derive(Clone, Debug)]
+pub(crate) enum SmolStr {
+    Heap(Arc<str>),
+    Inline {
+        len: u8,
+        buf: [u8; INLINE_CAP],
+    },
+}
+
+impl SmolStr {
+    pub fn new(text: &str) -> SmolStr {
+        let len = text.len();
+        if len <= INLINE_CAP {
+            let mut buf = [0; INLINE_CAP];
+            buf[..len].copy_from_slice(text.as_bytes());
+            SmolStr::Inline { len: len as u8, buf }
+        } else {
+            SmolStr::Heap(
+                text.to_string().into_boxed_str().into()
+            )
+        }
+    }
+
+    pub fn as_str(&self) -> &str {
+        match self {
+            SmolStr::Heap(data) => &*data,
+            SmolStr::Inline { len, buf } => {
+                let len = *len as usize;
+                let buf = &buf[..len];
+                unsafe { ::std::str::from_utf8_unchecked(buf) }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[cfg(target_pointer_width = "64")]
+    fn smol_str_is_smol() {
+        assert_eq!(::std::mem::size_of::<SmolStr>(), 8 + 8 + 8)
+    }
+
+    #[test]
+    fn test_round_trip() {
+        let mut text = String::new();
+        for n in 0..256 {
+            let smol = SmolStr::new(&text);
+            assert_eq!(smol.as_str(), text.as_str());
+            text.push_str(&n.to_string());
+        }
+    }
+}
+
diff --git a/src/yellow/green.rs b/src/yellow/green.rs
index 3ade46f45..26df76af6 100644
--- a/src/yellow/green.rs
+++ b/src/yellow/green.rs
@@ -1,5 +1,6 @@
 use std::sync::Arc;
 use {
+    smol_str::SmolStr,
     SyntaxKind::{self, *},
     TextUnit,
 };
@@ -116,7 +117,7 @@ pub(crate) enum GreenLeaf {
     },
     Token {
         kind: SyntaxKind,
-        text: Option<Arc<str>>,
+        text: Option<SmolStr>,
     },
 }
 
@@ -137,7 +138,7 @@ impl GreenLeaf {
                 debug_assert_eq!(t, text);
                 None
             }
-            None => Some(text.to_owned().into_boxed_str().into()),
+            None => Some(SmolStr::new(text)),
         };
         GreenLeaf::Token { kind, text }
     }
@@ -159,7 +160,7 @@ impl GreenLeaf {
             }
             GreenLeaf::Token { kind, text } => match text {
                 None => kind.static_text().unwrap(),
-                Some(t) => t,
+                Some(t) => t.as_str(),
             },
         }
     }