From fc99b981a184a7a408cadc0793e23a0e6bd7e747 Mon Sep 17 00:00:00 2001
From: Stephen Chung <Stephen.Chung@intexact.com>
Date: Fri, 1 May 2020 23:39:55 +0800
Subject: [PATCH] Fix panic when string character index is OOB.

---
 src/engine.rs   | 22 ++++++++++++++++------
 src/optimize.rs | 10 ++--------
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/src/engine.rs b/src/engine.rs
index cb92a5a9..c24b924c 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -1057,15 +1057,25 @@ impl Engine {
                     .as_int()
                     .map_err(|_| EvalAltResult::ErrorNumericIndexExpr(idx_pos))?;
 
-                let num_chars = s.chars().count();
-
                 if index >= 0 {
-                    let index = index as usize;
-                    let ch = s.chars().nth(index).unwrap();
-                    Ok(Target::StringChar(Box::new((val, index, ch.into()))))
+                    let ch = s.chars().nth(index as usize).ok_or_else(|| {
+                        Box::new(EvalAltResult::ErrorStringBounds(
+                            s.chars().count(),
+                            index,
+                            idx_pos,
+                        ))
+                    })?;
+
+                    Ok(Target::StringChar(Box::new((
+                        val,
+                        index as usize,
+                        ch.into(),
+                    ))))
                 } else {
                     Err(Box::new(EvalAltResult::ErrorStringBounds(
-                        num_chars, index, idx_pos,
+                        s.chars().count(),
+                        index,
+                        idx_pos,
                     )))
                 }
             }
diff --git a/src/optimize.rs b/src/optimize.rs
index 2a8fab4c..268c504a 100644
--- a/src/optimize.rs
+++ b/src/optimize.rs
@@ -435,9 +435,7 @@ fn optimize_expr<'a>(expr: Expr, state: &mut State<'a>) -> Expr {
                     .unwrap_or_else(|| Expr::Unit(pos))
             }
             // string[int]
-            (Expr::StringConstant(s, pos), Expr::IntegerConstant(i, _))
-                if i >= 0 && (i as usize) < s.chars().count() =>
-            {
+            (Expr::StringConstant(s, pos), Expr::IntegerConstant(i, _)) if i >= 0 && (i as usize) < s.chars().count() => {
                 // String literal indexing - get the character
                 state.set_dirty();
                 Expr::CharConstant(s.chars().nth(i as usize).expect("should get char"), pos)
@@ -550,11 +548,7 @@ fn optimize_expr<'a>(expr: Expr, state: &mut State<'a>) -> Expr {
                 optimize_expr(lhs, state)
             }
             // lhs || rhs
-            (lhs, rhs) => Expr::Or(
-                Box::new(optimize_expr(lhs, state)),
-                Box::new(optimize_expr(rhs, state)),
-                pos
-            ),
+            (lhs, rhs) => Expr::Or(Box::new(optimize_expr(lhs, state)), Box::new(optimize_expr(rhs, state)), pos),
         },
 
         // Do not call some special keywords