LibJS: Implement parsing and evaluation for AssignmentPatterns

e.g. `[...foo] = bar` can now be evaluated :^)

7 files changed, 104 insertions, 40 deletions

diff --git a/Userland/Libraries/LibJS/AST.cpp b/Userland/Libraries/LibJS/AST.cpp
index 06f548bb07..6abd3e48dd 100644
--- a/Userland/Libraries/LibJS/AST.cpp
+++ b/Userland/Libraries/LibJS/AST.cpp
@@ -1484,11 +1484,18 @@ Value AssignmentExpression::execute(Interpreter& interpreter, GlobalObject& glob
 {
     InterpreterNodeScope node_scope { interpreter, *this };
 
+#define EXECUTE_LHS()                                                     \
+    do {                                                                  \
+        if (auto* ptr = m_lhs.get_pointer<NonnullRefPtr<Expression>>()) { \
+            lhs_result = (*ptr)->execute(interpreter, global_object);     \
+            if (interpreter.exception())                                  \
+                return {};                                                \
+        }                                                                 \
+    } while (0)
+
 #define EXECUTE_LHS_AND_RHS()                                    \
     do {                                                         \
-        lhs_result = m_lhs->execute(interpreter, global_object); \
-        if (interpreter.exception())                             \
-            return {};                                           \
+        EXECUTE_LHS();                                           \
         rhs_result = m_rhs->execute(interpreter, global_object); \
         if (interpreter.exception())                             \
             return {};                                           \
@@ -1548,25 +1555,19 @@ Value AssignmentExpression::execute(Interpreter& interpreter, GlobalObject& glob
         rhs_result = unsigned_right_shift(global_object, lhs_result, rhs_result);
         break;
     case AssignmentOp::AndAssignment:
-        lhs_result = m_lhs->execute(interpreter, global_object);
-        if (interpreter.exception())
-            return {};
+        EXECUTE_LHS();
         if (!lhs_result.to_boolean())
             return lhs_result;
         rhs_result = m_rhs->execute(interpreter, global_object);
         break;
     case AssignmentOp::OrAssignment:
-        lhs_result = m_lhs->execute(interpreter, global_object);
-        if (interpreter.exception())
-            return {};
+        EXECUTE_LHS();
         if (lhs_result.to_boolean())
             return lhs_result;
         rhs_result = m_rhs->execute(interpreter, global_object);
         break;
     case AssignmentOp::NullishAssignment:
-        lhs_result = m_lhs->execute(interpreter, global_object);
-        if (interpreter.exception())
-            return {};
+        EXECUTE_LHS();
         if (!lhs_result.is_nullish())
             return lhs_result;
         rhs_result = m_rhs->execute(interpreter, global_object);
@@ -1575,26 +1576,42 @@ Value AssignmentExpression::execute(Interpreter& interpreter, GlobalObject& glob
     if (interpreter.exception())
         return {};
 
-    auto reference = m_lhs->to_reference(interpreter, global_object);
-    if (interpreter.exception())
-        return {};
+    return m_lhs.visit(
+        [&](NonnullRefPtr<Expression>& lhs) -> JS::Value {
+            auto reference = lhs->to_reference(interpreter, global_object);
+            if (interpreter.exception())
+                return {};
 
-    if (m_op == AssignmentOp::Assignment) {
-        rhs_result = m_rhs->execute(interpreter, global_object);
-        if (interpreter.exception())
-            return {};
-    }
+            if (m_op == AssignmentOp::Assignment) {
+                rhs_result = m_rhs->execute(interpreter, global_object);
+                if (interpreter.exception())
+                    return {};
+            }
 
-    if (reference.is_unresolvable()) {
-        interpreter.vm().throw_exception<ReferenceError>(global_object, ErrorType::InvalidLeftHandAssignment);
-        return {};
-    }
+            if (reference.is_unresolvable()) {
+                interpreter.vm().throw_exception<ReferenceError>(global_object, ErrorType::InvalidLeftHandAssignment);
+                return {};
+            }
 
-    reference.put_value(global_object, rhs_result);
-    if (interpreter.exception())
-        return {};
+            reference.put_value(global_object, rhs_result);
+            if (interpreter.exception())
+                return {};
 
-    return rhs_result;
+            return rhs_result;
+        },
+        [&](NonnullRefPtr<BindingPattern>& pattern) -> JS::Value {
+            VERIFY(m_op == AssignmentOp::Assignment);
+
+            rhs_result = m_rhs->execute(interpreter, global_object);
+            if (interpreter.exception())
+                return {};
+
+            interpreter.vm().assign(pattern, rhs_result, global_object);
+            if (interpreter.exception())
+                return {};
+
+            return rhs_result;
+        });
 }
 
 Value UpdateExpression::execute(Interpreter& interpreter, GlobalObject& global_object) const
@@ -1693,7 +1710,7 @@ void AssignmentExpression::dump(int indent) const
     ASTNode::dump(indent);
     print_indent(indent + 1);
     outln("{}", op_string);
-    m_lhs->dump(indent + 1);
+    m_lhs.visit([&](auto& lhs) { lhs->dump(indent + 1); });
     m_rhs->dump(indent + 1);
 }
 
@@ -2395,5 +2412,4 @@ void ScopeNode::add_hoisted_function(NonnullRefPtr<FunctionDeclaration> hoisted_
 {
     m_hoisted_functions.append(hoisted_function);
 }
-
 }
diff --git a/Userland/Libraries/LibJS/AST.h b/Userland/Libraries/LibJS/AST.h
index 27e3a6ff19..f3f3ad0673 100644
--- a/Userland/Libraries/LibJS/AST.h
+++ b/Userland/Libraries/LibJS/AST.h
@@ -998,13 +998,21 @@ public:
     {
     }
 
+    AssignmentExpression(SourceRange source_range, AssignmentOp op, NonnullRefPtr<BindingPattern> lhs, NonnullRefPtr<Expression> rhs)
+        : Expression(source_range)
+        , m_op(op)
+        , m_lhs(move(lhs))
+        , m_rhs(move(rhs))
+    {
+    }
+
     virtual Value execute(Interpreter&, GlobalObject&) const override;
     virtual void dump(int indent) const override;
     virtual void generate_bytecode(Bytecode::Generator&) const override;
 
 private:
     AssignmentOp m_op;
-    NonnullRefPtr<Expression> m_lhs;
+    Variant<NonnullRefPtr<Expression>, NonnullRefPtr<BindingPattern>> m_lhs;
     NonnullRefPtr<Expression> m_rhs;
 };
 
diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index 6418a56a5d..768df2214c 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -272,8 +272,10 @@ void Identifier::generate_bytecode(Bytecode::Generator& generator) const
 
 void AssignmentExpression::generate_bytecode(Bytecode::Generator& generator) const
 {
-    if (is<Identifier>(*m_lhs)) {
-        auto& identifier = static_cast<Identifier const&>(*m_lhs);
+    // FIXME: Implement this for BindingPatterns too.
+    auto& lhs = m_lhs.get<NonnullRefPtr<Expression>>();
+    if (is<Identifier>(*lhs)) {
+        auto& identifier = static_cast<Identifier const&>(*lhs);
 
         if (m_op == AssignmentOp::Assignment) {
             m_rhs->generate_bytecode(generator);
@@ -281,7 +283,7 @@ void AssignmentExpression::generate_bytecode(Bytecode::Generator& generator) con
             return;
         }
 
-        m_lhs->generate_bytecode(generator);
+        lhs->generate_bytecode(generator);
 
         Bytecode::BasicBlock* rhs_block_ptr { nullptr };
         Bytecode::BasicBlock* end_block_ptr { nullptr };
@@ -377,8 +379,8 @@ void AssignmentExpression::generate_bytecode(Bytecode::Generator& generator) con
         return;
     }
 
-    if (is<MemberExpression>(*m_lhs)) {
-        auto& expression = static_cast<MemberExpression const&>(*m_lhs);
+    if (is<MemberExpression>(*lhs)) {
+        auto& expression = static_cast<MemberExpression const&>(*lhs);
         expression.object().generate_bytecode(generator);
         auto object_reg = generator.allocate_register();
         generator.emit<Bytecode::Op::Store>(object_reg);
diff --git a/Userland/Libraries/LibJS/Lexer.cpp b/Userland/Libraries/LibJS/Lexer.cpp
index 0263231065..daeffc53d6 100644
--- a/Userland/Libraries/LibJS/Lexer.cpp
+++ b/Userland/Libraries/LibJS/Lexer.cpp
@@ -20,7 +20,7 @@ HashMap<char, TokenType> Lexer::s_single_char_tokens;
 
 Lexer::Lexer(StringView source, StringView filename, size_t line_number, size_t line_column)
     : m_source(source)
-    , m_current_token(TokenType::Eof, {}, StringView(nullptr), StringView(nullptr), filename, 0, 0)
+    , m_current_token(TokenType::Eof, {}, StringView(nullptr), StringView(nullptr), filename, 0, 0, 0)
     , m_filename(filename)
     , m_line_number(line_number)
     , m_line_column(line_column)
@@ -659,7 +659,8 @@ Token Lexer::next()
         m_source.substring_view(value_start - 1, m_position - value_start),
         m_filename,
         value_start_line_number,
-        value_start_column_number);
+        value_start_column_number,
+        m_position);
 
     if constexpr (LEXER_DEBUG) {
         dbgln("------------------------------");
diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index feaf0ec9bc..09d652b56b 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -1305,6 +1305,36 @@ NonnullRefPtr<AssignmentExpression> Parser::parse_assignment_expression(Assignme
         || match(TokenType::DoublePipeEquals)
         || match(TokenType::DoubleQuestionMarkEquals));
     consume();
+
+    if (assignment_op == AssignmentOp::Assignment) {
+        auto synthesize_binding_pattern = [this](Expression const& expression) -> RefPtr<BindingPattern> {
+            // Clear any syntax error that has occurred in the range that 'expression' spans.
+            m_state.errors.remove_all_matching([range = expression.source_range()](auto const& error) {
+                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);
+            Lexer lexer { source, m_state.lexer.filename(), expression.source_range().start.line, expression.source_range().start.column };
+            Parser parser { lexer };
+            auto result = parser.parse_binding_pattern();
+            if (parser.has_errors()) {
+                for (auto& error : parser.errors())
+                    syntax_error(move(error.message), move(error.position));
+            }
+            return result;
+        };
+        if (is<ArrayExpression>(*lhs) || is<ObjectExpression>(*lhs)) {
+            auto binding_pattern = synthesize_binding_pattern(*lhs);
+            if (binding_pattern) {
+                auto rhs = parse_expression(min_precedence, associativity);
+                return create_ast_node<AssignmentExpression>(
+                    { m_state.current_token.filename(), rule_start.position(), position() },
+                    assignment_op,
+                    binding_pattern.release_nonnull(),
+                    move(rhs));
+            }
+        }
+    }
     if (!is<Identifier>(*lhs) && !is<MemberExpression>(*lhs) && !is<CallExpression>(*lhs)) {
         syntax_error("Invalid left-hand side in assignment");
     } else if (m_state.strict_mode && is<Identifier>(*lhs)) {
@@ -2398,7 +2428,8 @@ Position Parser::position() const
 {
     return {
         m_state.current_token.line_number(),
-        m_state.current_token.line_column()
+        m_state.current_token.line_column(),
+        m_state.current_token.offset(),
     };
 }
 
diff --git a/Userland/Libraries/LibJS/SourceRange.h b/Userland/Libraries/LibJS/SourceRange.h
index 936863ecc7..b92208dc32 100644
--- a/Userland/Libraries/LibJS/SourceRange.h
+++ b/Userland/Libraries/LibJS/SourceRange.h
@@ -13,9 +13,12 @@ namespace JS {
 struct Position {
     size_t line { 0 };
     size_t column { 0 };
+    size_t offset { 0 };
 };
 
 struct SourceRange {
+    [[nodiscard]] bool contains(Position const& position) const { return position.offset <= end.offset && position.offset >= start.offset; }
+
     StringView filename;
     Position start;
     Position end;
diff --git a/Userland/Libraries/LibJS/Token.h b/Userland/Libraries/LibJS/Token.h
index bb3c2bb324..1a9033c8f1 100644
--- a/Userland/Libraries/LibJS/Token.h
+++ b/Userland/Libraries/LibJS/Token.h
@@ -161,7 +161,7 @@ enum class TokenCategory {
 
 class Token {
 public:
-    Token(TokenType type, String message, StringView trivia, StringView value, StringView filename, size_t line_number, size_t line_column)
+    Token(TokenType type, String message, StringView trivia, StringView value, StringView filename, size_t line_number, size_t line_column, size_t offset)
         : m_type(type)
         , m_message(message)
         , m_trivia(trivia)
@@ -169,6 +169,7 @@ public:
         , m_filename(filename)
         , m_line_number(line_number)
         , m_line_column(line_column)
+        , m_offset(offset)
     {
     }
 
@@ -184,6 +185,7 @@ public:
     const StringView& filename() const { return m_filename; }
     size_t line_number() const { return m_line_number; }
     size_t line_column() const { return m_line_column; }
+    size_t offset() const { return m_offset; }
     double double_value() const;
     bool bool_value() const;
 
@@ -207,6 +209,7 @@ private:
     StringView m_filename;
     size_t m_line_number;
     size_t m_line_column;
+    size_t m_offset;
 };
 
 }