1 files changed, 104 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/parsing/parser_impl/input.rs b/crates/ra_syntax/src/parsing/parser_impl/input.rs
new file mode 100644
index 000000000..275d94918
--- /dev/null
+++ b/crates/ra_syntax/src/parsing/parser_impl/input.rs
@@ -0,0 +1,104 @@
+use crate::{
+    SyntaxKind, SyntaxKind::EOF, TextRange, TextUnit,
+    parsing::lexer::Token,
+};
+
+use std::ops::{Add, AddAssign};
+
+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 }
+    }
+
+    /// Get the syntax kind of token at given input position.
+    pub fn kind(&self, pos: InputPosition) -> SyntaxKind {
+        let idx = pos.0 as usize;
+        if !(idx < self.tokens.len()) {
+            return EOF;
+        }
+        self.tokens[idx].kind
+    }
+
+    /// Get the length of a token at given input position.
+    pub fn token_len(&self, pos: InputPosition) -> TextUnit {
+        let idx = pos.0 as usize;
+        if !(idx < self.tokens.len()) {
+            return 0.into();
+        }
+        self.tokens[idx].len
+    }
+
+    /// Get the start position of a taken at given input position.
+    pub fn token_start_at(&self, pos: InputPosition) -> TextUnit {
+        let idx = pos.0 as usize;
+        if !(idx < self.tokens.len()) {
+            return 0.into();
+        }
+        self.start_offsets[idx]
+    }
+
+    /// Get the raw text of a token at given input position.
+    pub fn token_text(&self, pos: InputPosition) -> &'t str {
+        let idx = pos.0 as usize;
+        if !(idx < self.tokens.len()) {
+            return "";
+        }
+        let range = TextRange::offset_len(self.start_offsets[idx], self.tokens[idx].len);
+        &self.text[range]
+    }
+}
+
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub(crate) struct InputPosition(u32);
+
+impl InputPosition {
+    pub fn new() -> Self {
+        InputPosition(0)
+    }
+}
+
+impl Add<u32> for InputPosition {
+    type Output = InputPosition;
+
+    fn add(self, rhs: u32) -> InputPosition {
+        InputPosition(self.0 + rhs)
+    }
+}
+
+impl AddAssign<u32> for InputPosition {
+    fn add_assign(&mut self, rhs: u32) {
+        self.0 += rhs
+    }
+}