1 files changed, 130 insertions, 0 deletions
diff --git a/cli/ast/source_file_info.rs b/cli/ast/source_file_info.rs
new file mode 100644
index 000000000..5792fb419
--- /dev/null
+++ b/cli/ast/source_file_info.rs
@@ -0,0 +1,130 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+use super::Location;
+
+use swc_common::BytePos;
+
+pub struct SourceFileInfo {
+  pub specifier: String,
+  pub text: String,
+  line_start_byte_positions: Vec<BytePos>,
+}
+
+impl SourceFileInfo {
+  pub fn new(specifier: &str, text: &str) -> SourceFileInfo {
+    SourceFileInfo {
+      line_start_byte_positions: get_line_start_positions(text),
+      specifier: specifier.to_string(),
+      text: text.to_string(),
+    }
+  }
+
+  pub fn get_location(&self, pos: BytePos) -> Location {
+    let line_index = self.get_line_index_at_pos(pos);
+    let col = self.get_column_on_line_index_at_pos(line_index, pos);
+
+    Location {
+      specifier: self.specifier.clone(),
+      // todo(dsherret): this is temporarily 1-indexed in order to have
+      // the same behaviour as swc, but we should change this to be 0-indexed
+      // in order to be the same as the LSP.
+      line: line_index + 1,
+      col,
+    }
+  }
+
+  fn get_line_index_at_pos(&self, pos: BytePos) -> usize {
+    match self.line_start_byte_positions.binary_search(&pos) {
+      Ok(index) => index,
+      Err(insert_index) => insert_index - 1,
+    }
+  }
+
+  fn get_column_on_line_index_at_pos(
+    &self,
+    line_index: usize,
+    pos: BytePos,
+  ) -> usize {
+    assert!(line_index < self.line_start_byte_positions.len());
+    let pos = pos.0 as usize;
+    let line_start_pos = self.line_start_byte_positions[line_index].0 as usize;
+    let line_end_pos = self
+      .line_start_byte_positions
+      .get(line_index + 1)
+      // may include line feed chars at the end, but in that case the pos should be less
+      .map(|p| p.0 as usize)
+      .unwrap_or_else(|| self.text.len());
+    let line_text = &self.text[line_start_pos..line_end_pos];
+
+    if pos < line_start_pos {
+      panic!(
+        "byte position {} was less than the start line position of {}",
+        pos, line_start_pos
+      );
+    } else if pos > line_end_pos {
+      panic!(
+        "byte position {} exceeded the end line position of {}",
+        pos, line_end_pos
+      );
+    } else if pos == line_end_pos {
+      line_text.chars().count()
+    } else {
+      line_text
+        .char_indices()
+        .position(|(c_pos, _)| line_start_pos + c_pos >= pos)
+        .unwrap()
+    }
+  }
+}
+
+fn get_line_start_positions(text: &str) -> Vec<BytePos> {
+  let mut result = vec![BytePos(0)];
+  for (pos, c) in text.char_indices() {
+    if c == '\n' {
+      let line_start_pos = BytePos((pos + 1) as u32);
+      result.push(line_start_pos);
+    }
+  }
+  result
+}
+
+#[cfg(test)]
+mod test {
+  use super::SourceFileInfo;
+  use crate::ast::Location;
+
+  use swc_common::BytePos;
+
+  #[test]
+  fn should_provide_locations() {
+    let text = "12\n3\r\n4\n5";
+    let specifier = "file:///file.ts";
+    let info = SourceFileInfo::new(specifier, text);
+    assert_pos_line_and_col(&info, 0, 1, 0); // 1
+    assert_pos_line_and_col(&info, 1, 1, 1); // 2
+    assert_pos_line_and_col(&info, 2, 1, 2); // \n
+    assert_pos_line_and_col(&info, 3, 2, 0); // 3
+    assert_pos_line_and_col(&info, 4, 2, 1); // \r
+    assert_pos_line_and_col(&info, 5, 2, 2); // \n
+    assert_pos_line_and_col(&info, 6, 3, 0); // 4
+    assert_pos_line_and_col(&info, 7, 3, 1); // \n
+    assert_pos_line_and_col(&info, 8, 4, 0); // 5
+    assert_pos_line_and_col(&info, 9, 4, 1); // <EOF>
+  }
+
+  fn assert_pos_line_and_col(
+    info: &SourceFileInfo,
+    pos: u32,
+    line: usize,
+    col: usize,
+  ) {
+    assert_eq!(
+      info.get_location(BytePos(pos)),
+      Location {
+        specifier: info.specifier.clone(),
+        line,
+        col,
+      }
+    );
+  }
+}