1 files changed, 144 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/syntax_text.rs b/crates/ra_syntax/src/syntax_text.rs
new file mode 100644
index 000000000..84e5b231a
--- /dev/null
+++ b/crates/ra_syntax/src/syntax_text.rs
@@ -0,0 +1,144 @@
+use std::{fmt, ops};
+
+use crate::{SyntaxNode, TextRange, TextUnit};
+
+#[derive(Clone)]
+pub struct SyntaxText<'a> {
+    node: &'a SyntaxNode,
+    range: TextRange,
+}
+
+impl<'a> SyntaxText<'a> {
+    pub(crate) fn new(node: &'a SyntaxNode) -> SyntaxText<'a> {
+        SyntaxText { node, range: node.range() }
+    }
+
+    pub fn chunks(&self) -> impl Iterator<Item = &'a str> {
+        let range = self.range;
+        self.node.descendants().filter_map(move |node| {
+            let text = node.leaf_text()?;
+            let range = range.intersection(&node.range())?;
+            let range = range - node.range().start();
+            Some(&text[range])
+        })
+    }
+
+    pub fn push_to(&self, buf: &mut String) {
+        self.chunks().for_each(|it| buf.push_str(it));
+    }
+
+    pub fn to_string(&self) -> String {
+        self.chunks().collect()
+    }
+
+    pub fn contains(&self, c: char) -> bool {
+        self.chunks().any(|it| it.contains(c))
+    }
+
+    pub fn find(&self, c: char) -> Option<TextUnit> {
+        let mut acc: TextUnit = 0.into();
+        for chunk in self.chunks() {
+            if let Some(pos) = chunk.find(c) {
+                let pos: TextUnit = (pos as u32).into();
+                return Some(acc + pos);
+            }
+            acc += TextUnit::of_str(chunk);
+        }
+        None
+    }
+
+    pub fn len(&self) -> TextUnit {
+        self.range.len()
+    }
+
+    pub fn slice(&self, range: impl SyntaxTextSlice) -> SyntaxText<'a> {
+        let range = range.restrict(self.range).unwrap_or_else(|| {
+            panic!("invalid slice, range: {:?}, slice: {:?}", self.range, range)
+        });
+        SyntaxText { node: self.node, range }
+    }
+
+    pub fn char_at(&self, offset: impl Into<TextUnit>) -> Option<char> {
+        let mut start: TextUnit = 0.into();
+        let offset = offset.into();
+        for chunk in self.chunks() {
+            let end = start + TextUnit::of_str(chunk);
+            if start <= offset && offset < end {
+                let off: usize = u32::from(offset - start) as usize;
+                return Some(chunk[off..].chars().next().unwrap());
+            }
+            start = end;
+        }
+        None
+    }
+}
+
+impl<'a> fmt::Debug for SyntaxText<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.to_string(), f)
+    }
+}
+
+impl<'a> fmt::Display for SyntaxText<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.to_string(), f)
+    }
+}
+
+pub trait SyntaxTextSlice: fmt::Debug {
+    fn restrict(&self, range: TextRange) -> Option<TextRange>;
+}
+
+impl SyntaxTextSlice for TextRange {
+    fn restrict(&self, range: TextRange) -> Option<TextRange> {
+        self.intersection(&range)
+    }
+}
+
+impl SyntaxTextSlice for ops::RangeTo<TextUnit> {
+    fn restrict(&self, range: TextRange) -> Option<TextRange> {
+        if !range.contains_inclusive(self.end) {
+            return None;
+        }
+        Some(TextRange::from_to(range.start(), self.end))
+    }
+}
+
+impl SyntaxTextSlice for ops::RangeFrom<TextUnit> {
+    fn restrict(&self, range: TextRange) -> Option<TextRange> {
+        if !range.contains_inclusive(self.start) {
+            return None;
+        }
+        Some(TextRange::from_to(self.start, range.end()))
+    }
+}
+
+impl SyntaxTextSlice for ops::Range<TextUnit> {
+    fn restrict(&self, range: TextRange) -> Option<TextRange> {
+        TextRange::from_to(self.start, self.end).restrict(range)
+    }
+}
+
+impl From<SyntaxText<'_>> for String {
+    fn from(text: SyntaxText) -> String {
+        text.to_string()
+    }
+}
+
+impl PartialEq<str> for SyntaxText<'_> {
+    fn eq(&self, mut rhs: &str) -> bool {
+        for chunk in self.chunks() {
+            if !rhs.starts_with(chunk) {
+                return false;
+            }
+            rhs = &rhs[chunk.len()..];
+        }
+        rhs.is_empty()
+    }
+}
+
+impl PartialEq<&'_ str> for SyntaxText<'_> {
+    fn eq(&self, rhs: &&str) -> bool {
+        self == *rhs
+    }
+}