fix: Tokens only extend to the end of the line

Previously, when looking up a line and column, we would always return
the token at or immediately before that position, even if it belonged
to an earlier minified line. This is
1. wrong—tokens are only meant to extend to the end of a line.
2. inconsistent—this means that an unmapped line before any mapped line
   would return no mapping, but an unmapped line after a mapped line
   would.

Author: loewenheim

src/types.rs

@@ -713,6 +713,13 @@ impl SourceMap {
         let (idx, raw) =
             greatest_lower_bound(&self.tokens, &(line, col), |t| (t.dst_line, t.dst_col))?;
 
+        // If the token has a lower minified line number,
+        // it actually belongs to the previous line. That means it should
+        // not match.
+        if raw.dst_line < line {
+            return None;
+        }
+
         let mut token = Token {
             raw,
             sm: self,

tests/test_index.rs

@@ -100,10 +100,11 @@ fn test_basic_indexed_sourcemap() {
         ism.lookup_token(0, 0).unwrap().to_tuple(),
         ("file1.js", 0, 0, None)
     );
-    assert_eq!(
-        ism.lookup_token(1, 0).unwrap().to_tuple(),
-        ("file1.js", 2, 12, Some("b"))
-    );
+
+    // Line 1, column 0 (zero-based) falls into the first section,
+    // but there are no mappings for line 1 there.
+    assert!(ism.lookup_token(1, 0).is_none());
+
     assert_eq!(
         ism.lookup_token(1, 1).unwrap().to_tuple(),
         ("file2.js", 0, 0, None)

tests/test_regular.rs

@@ -29,11 +29,8 @@ fn test_basic_sourcemap() {
         ("coolstuff.js", 2, 8, None)
     );
 
-    // Token can return prior lines.
-    assert_eq!(
-        sm.lookup_token(1000, 0).unwrap().to_tuple(),
-        ("coolstuff.js", 2, 8, None)
-    );
+    // There are no mappings for line 1000.
+    assert!(sm.lookup_token(1000, 0).is_none());
 }
 
 #[test]