1 files changed, 54 insertions, 0 deletions
diff --git a/devtools/client/debugger/src/utils/editor/get-expression.js b/devtools/client/debugger/src/utils/editor/get-expression.js
new file mode 100644
index 0000000000..c664f163c3
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/get-expression.js
@@ -0,0 +1,54 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function tokenAtTextPosition(cm, { line, column }) {
+  if (line < 0 || line >= cm.lineCount()) {
+    return null;
+  }
+
+  const token = cm.getTokenAt({ line: line - 1, ch: column });
+  if (!token) {
+    return null;
+  }
+
+  return { startColumn: token.start, endColumn: token.end, type: token.type };
+}
+
+// The strategy of querying codeMirror tokens was borrowed
+// from Chrome's inital implementation in JavaScriptSourceFrame.js#L414
+export function getExpressionFromCoords(cm, coord) {
+  const token = tokenAtTextPosition(cm, coord);
+  if (!token) {
+    return null;
+  }
+
+  let startHighlight = token.startColumn;
+  const endHighlight = token.endColumn;
+  const lineNumber = coord.line;
+  const line = cm.doc.getLine(coord.line - 1);
+  while (startHighlight > 1 && line.charAt(startHighlight - 1) === ".") {
+    const tokenBefore = tokenAtTextPosition(cm, {
+      line: coord.line,
+      column: startHighlight - 2,
+    });
+
+    if (!tokenBefore || !tokenBefore.type) {
+      return null;
+    }
+
+    startHighlight = tokenBefore.startColumn;
+  }
+
+  const expression = line.substring(startHighlight, endHighlight) || "";
+
+  if (!expression) {
+    return null;
+  }
+
+  const location = {
+    start: { line: lineNumber, column: startHighlight },
+    end: { line: lineNumber, column: endHighlight },
+  };
+  return { expression, location };
+}