1 files changed, 68 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/parsing/input.rs b/crates/ra_syntax/src/parsing/input.rs
new file mode 100644
index 000000000..96c03bb11
--- /dev/null
+++ b/crates/ra_syntax/src/parsing/input.rs
@@ -0,0 +1,68 @@
+use crate::{
+    SyntaxKind, SyntaxKind::EOF, TextRange, TextUnit,
+    parsing::{
+        TokenSource,
+        lexer::Token,
+    },
+};
+
+impl<'t> TokenSource for ParserInput<'t> {
+    fn token_kind(&self, pos: usize) -> SyntaxKind {
+        if !(pos < self.tokens.len()) {
+            return EOF;
+        }
+        self.tokens[pos].kind
+    }
+    fn is_token_joint_to_next(&self, pos: usize) -> bool {
+        if !(pos + 1 < self.tokens.len()) {
+            return true;
+        }
+        self.start_offsets[pos] + self.tokens[pos].len == self.start_offsets[pos + 1]
+    }
+    fn is_keyword(&self, pos: usize, kw: &str) -> bool {
+        if !(pos < self.tokens.len()) {
+            return false;
+        }
+        let range = TextRange::offset_len(self.start_offsets[pos], self.tokens[pos].len);
+
+        self.text[range] == *kw
+    }
+}
+
+pub(crate) struct ParserInput<'t> {
+    text: &'t str,
+    /// start position of each token(expect whitespace and comment)
+    /// ```non-rust
+    ///  struct Foo;
+    /// ^------^---
+    /// |      |  ^-
+    /// 0      7  10
+    /// ```
+    /// (token, start_offset): `[(struct, 0), (Foo, 7), (;, 10)]`
+    start_offsets: Vec<TextUnit>,
+    /// non-whitespace/comment tokens
+    /// ```non-rust
+    /// struct Foo {}
+    /// ^^^^^^ ^^^ ^^
+    /// ```
+    /// tokens: `[struct, Foo, {, }]`
+    tokens: Vec<Token>,
+}
+
+impl<'t> ParserInput<'t> {
+    /// Generate input from tokens(expect comment and whitespace).
+    pub fn new(text: &'t str, raw_tokens: &'t [Token]) -> ParserInput<'t> {
+        let mut tokens = Vec::new();
+        let mut start_offsets = Vec::new();
+        let mut len = 0.into();
+        for &token in raw_tokens.iter() {
+            if !token.kind.is_trivia() {
+                tokens.push(token);
+                start_offsets.push(len);
+            }
+            len += token.len;
+        }
+
+        ParserInput { text, start_offsets, tokens }
+    }
+}