LibJS: Set Token's m_offset to the value's start index

This makes much more sense than the current way of setting it to the
Lexer's m_position after consuming the full value.

2 files changed, 9 insertions, 4 deletions

diff --git a/Userland/Libraries/LibJS/Lexer.cpp b/Userland/Libraries/LibJS/Lexer.cpp
index a71469f362..685e915d2b 100644
--- a/Userland/Libraries/LibJS/Lexer.cpp
+++ b/Userland/Libraries/LibJS/Lexer.cpp
@@ -832,7 +832,7 @@ Token Lexer::next()
             m_filename,
             m_line_number,
             m_line_column - 1,
-            m_position);
+            value_start + 1);
         m_hit_invalid_unicode.clear();
         // Do not produce any further tokens.
         VERIFY(is_eof());
@@ -845,7 +845,7 @@ Token Lexer::next()
             m_filename,
             value_start_line_number,
             value_start_column_number,
-            m_position);
+            value_start - 1);
     }
 
     if (identifier.has_value())
@@ -889,7 +889,7 @@ Token Lexer::force_slash_as_regex()
         m_filename,
         m_current_token.line_number(),
         m_current_token.line_column(),
-        m_position);
+        value_start - 1);
 
     if constexpr (LEXER_DEBUG) {
         dbgln("------------------------------");
diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index 6772e2fff8..9b6e353c2f 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -2138,7 +2138,12 @@ RefPtr<BindingPattern> Parser::synthesize_binding_pattern(Expression const& expr
         return error.position.has_value() && range.contains(*error.position);
     });
     // Make a parser and parse the source for this expression as a binding pattern.
-    auto source = m_state.lexer.source().substring_view(expression.source_range().start.offset - 2, expression.source_range().end.offset - expression.source_range().start.offset);
+    // NOTE: There's currently a fundamental problem that we pass the *next* (a.k.a. `current_token`)
+    // token's position to most nodes' SourceRange when using `rule_start.position(), position()`.
+    // This means that `source` will contain the subsequent token's trivia, if any (which is fine).
+    auto source_start_offset = expression.source_range().start.offset;
+    auto source_end_offset = expression.source_range().end.offset;
+    auto source = m_state.lexer.source().substring_view(source_start_offset, source_end_offset - source_start_offset);
     Lexer lexer { source, m_state.lexer.filename(), expression.source_range().start.line, expression.source_range().start.column };
     Parser parser { lexer };