starlark: Support parsing member expressions

starlark/ast.h

@@ -35,6 +35,7 @@ struct DictExpr;
 struct ListExpr;
 struct ListComp;
 struct SliceExpr;
+struct MemberExpr;
 
 using Expression = std::variant<
     CallExpr,
@@ -44,7 +45,8 @@ using Expression = std::variant<
     ListComp,
     ListExpr,
     DictExpr,
-    SliceExpr>;
+    SliceExpr,
+    MemberExpr>;
 
 struct Argument;
 
@@ -66,6 +68,12 @@ struct SliceExpr {
     constexpr bool operator==(SliceExpr const &) const;
 };
 
+struct MemberExpr {
+    std::shared_ptr<Expression> target;
+    Identifier member;
+    constexpr bool operator==(MemberExpr const &) const;
+};
+
 // TODO(robinlinden): shared_ptr is silly here, but right now the ast has to be
 // copyable for some reason.
 struct ListComp {
@@ -100,6 +108,10 @@ constexpr bool ListComp::operator==(ListComp const &o) const {
     return *element == *o.element && iterator_var == o.iterator_var && *iterable == *o.iterable;
 }
 
+constexpr bool MemberExpr::operator==(MemberExpr const &o) const {
+    return *target == *o.target && member == o.member;
+}
+
 struct AssignStmt {
     Identifier target;
     Expression value;

starlark/parser.h

@@ -313,6 +313,17 @@ class Parser {
                 .target = std::make_shared<Expression>(std::move(*operand)),
                 .index = std::make_shared<Expression>(std::move(*index_expr)),
             };
+        } else if (std::holds_alternative<token::Dot>(*next)) {
+            auto member_token = next_token();
+            if (!member_token || !std::holds_alternative<token::Identifier>(*member_token)) {
+                std::cerr << "Expected identifier after '.'.\n";
+                return std::nullopt;
+            }
+
+            return MemberExpr{
+                .target = std::make_shared<Expression>(std::move(*operand)),
+                .member = Identifier{.name = std::get<token::Identifier>(*member_token).name},
+            };
         } else {
             reconsume(std::move(*next));
         }

starlark/parser_test.cc

@@ -276,6 +276,22 @@ int main() {
                 },
             },
         },
+        {
+            "foo.bar",
+            starlark::Program{
+                .statements{
+                    starlark::ExpressionStmt{
+                        .expr{
+                            starlark::MemberExpr{
+                                .target = std::make_shared<starlark::Expression>(
+                                    starlark::Identifier{"foo"}),
+                                .member = starlark::Identifier{"bar"},
+                            },
+                        },
+                    },
+                },
+            },
+        },
     });
 
     // TODO(robinlinden): Return error codes from parser and use that here.
@@ -326,6 +342,12 @@ int main() {
         "A = foo(",
         // Non-ident target.
         "\"A\" = B",
+
+        // MemberExpr
+        // Missing member name.
+        "foo.",
+        // Invalid member name.
+        "foo.5",
     });
 
     etest::Suite s{};