Parse dict[str, i32] style annotation

Author: namannimmo10

src/lpython/semantics/python_ast_to_asr.cpp

@@ -204,6 +204,20 @@ class CommonVisitor : public AST::BaseVisitor<Derived> {
                     throw SemanticError("Only Name in Subscript supported for now in `set`"
                         " annotation", loc);
                 }
+            } else if (var_annotation == "dict") {
+                if (AST::is_a<AST::Tuple_t>(*s->m_slice)) {
+                    AST::Tuple_t *t = AST::down_cast<AST::Tuple_t>(s->m_slice);
+                    if (t->n_elts != 2) {
+                        throw SemanticError("`dict` annotation must have 2 elements: types"
+                            " of both keys and values", loc);
+                    }
+                    ASR::ttype_t *key_type = ast_expr_to_asr_type(loc, *t->m_elts[0]);
+                    ASR::ttype_t *value_type = ast_expr_to_asr_type(loc, *t->m_elts[1]);
+                    return ASRUtils::TYPE(ASR::make_Dict_t(al, loc, key_type, value_type));
+                } else {
+                    throw SemanticError("`dict` annotation must have 2 elements: types of"
+                        " both keys and values", loc);
+                }
             } else {
                 ASR::dimension_t dim;
                 dim.loc = loc;