1 files changed, 307 insertions, 0 deletions
diff --git a/cli/ast/transforms.rs b/cli/ast/transforms.rs
new file mode 100644
index 000000000..570a0bf5b
--- /dev/null
+++ b/cli/ast/transforms.rs
@@ -0,0 +1,307 @@
+use swc_common::DUMMY_SP;
+use swc_ecmascript::ast as swc_ast;
+use swc_ecmascript::visit::noop_fold_type;
+use swc_ecmascript::visit::Fold;
+
+/// Transforms import declarations to variable declarations
+/// with a dynamic import. This is used to provide import
+/// declaration support in the REPL.
+pub struct DownlevelImportsFolder;
+
+impl Fold for DownlevelImportsFolder {
+  noop_fold_type!(); // skip typescript specific nodes
+
+  fn fold_module_item(
+    &mut self,
+    module_item: swc_ast::ModuleItem,
+  ) -> swc_ast::ModuleItem {
+    use swc_ecmascript::ast::*;
+
+    match &module_item {
+      ModuleItem::ModuleDecl(ModuleDecl::Import(import_decl)) => {
+        // Handle type only imports
+        if import_decl.type_only {
+          return ModuleItem::Stmt(Stmt::Empty(EmptyStmt { span: DUMMY_SP }));
+        }
+
+        // The initializer (ex. `await import('./mod.ts')`)
+        let initializer = Box::new(Expr::Await(AwaitExpr {
+          span: DUMMY_SP,
+          arg: Box::new(Expr::Call(CallExpr {
+            span: DUMMY_SP,
+            callee: ExprOrSuper::Expr(Box::new(Expr::Ident(Ident {
+              span: DUMMY_SP,
+              sym: "import".into(),
+              optional: false,
+            }))),
+            args: vec![ExprOrSpread {
+              spread: None,
+              expr: Box::new(Expr::Lit(Lit::Str(Str {
+                span: DUMMY_SP,
+                has_escape: false,
+                kind: StrKind::Normal {
+                  contains_quote: false,
+                },
+                value: import_decl.src.value.clone(),
+              }))),
+            }],
+            type_args: None,
+          })),
+        }));
+
+        // Handle imports for the side effects
+        // ex. `import "module.ts"` -> `await import("module.ts");`
+        if import_decl.specifiers.is_empty() {
+          return ModuleItem::Stmt(Stmt::Expr(ExprStmt {
+            span: DUMMY_SP,
+            expr: initializer,
+          }));
+        }
+
+        // Collect the specifiers and create the variable statement
+        let named_import_props = import_decl
+          .specifiers
+          .iter()
+          .filter_map(|specifier| match specifier {
+            ImportSpecifier::Default(specifier) => Some(create_key_value(
+              "default".to_string(),
+              specifier.local.sym.to_string(),
+            )),
+            ImportSpecifier::Named(specifier) => {
+              Some(match specifier.imported.as_ref() {
+                Some(name) => create_key_value(
+                  name.sym.to_string(),
+                  specifier.local.sym.to_string(),
+                ),
+                None => create_assignment(specifier.local.sym.to_string()),
+              })
+            }
+            ImportSpecifier::Namespace(_) => None,
+          })
+          .collect::<Vec<_>>();
+        let namespace_import_name =
+          import_decl
+            .specifiers
+            .iter()
+            .find_map(|specifier| match specifier {
+              ImportSpecifier::Namespace(specifier) => {
+                Some(create_binding_ident(specifier.local.sym.to_string()))
+              }
+              _ => None,
+            });
+
+        ModuleItem::Stmt(Stmt::Decl(Decl::Var(VarDecl {
+          span: DUMMY_SP,
+          kind: VarDeclKind::Const,
+          declare: false,
+          decls: {
+            let mut decls = Vec::new();
+
+            if !named_import_props.is_empty() {
+              decls.push(VarDeclarator {
+                span: DUMMY_SP,
+                name: Pat::Object(ObjectPat {
+                  span: DUMMY_SP,
+                  optional: false,
+                  props: named_import_props,
+                  type_ann: None,
+                }),
+                definite: false,
+                init: Some(initializer.clone()),
+              });
+            }
+            if let Some(namespace_import) = namespace_import_name {
+              decls.push(VarDeclarator {
+                span: DUMMY_SP,
+                name: Pat::Ident(namespace_import),
+                definite: false,
+                init: Some(initializer),
+              });
+            }
+
+            decls
+          },
+        })))
+      }
+      _ => module_item,
+    }
+  }
+}
+
+fn create_binding_ident(name: String) -> swc_ast::BindingIdent {
+  swc_ast::BindingIdent {
+    id: create_ident(name),
+    type_ann: None,
+  }
+}
+
+fn create_ident(name: String) -> swc_ast::Ident {
+  swc_ast::Ident {
+    span: DUMMY_SP,
+    sym: name.into(),
+    optional: false,
+  }
+}
+
+fn create_key_value(key: String, value: String) -> swc_ast::ObjectPatProp {
+  swc_ast::ObjectPatProp::KeyValue(swc_ast::KeyValuePatProp {
+    key: swc_ast::PropName::Ident(swc_ast::Ident {
+      span: DUMMY_SP,
+      sym: key.into(),
+      optional: false,
+    }),
+    value: Box::new(swc_ast::Pat::Ident(swc_ast::BindingIdent {
+      id: swc_ast::Ident {
+        span: DUMMY_SP,
+        sym: value.into(),
+        optional: false,
+      },
+      type_ann: None,
+    })),
+  })
+}
+
+fn create_assignment(key: String) -> swc_ast::ObjectPatProp {
+  swc_ast::ObjectPatProp::Assign(swc_ast::AssignPatProp {
+    span: DUMMY_SP,
+    key: create_ident(key),
+    value: None,
+  })
+}
+
+#[cfg(test)]
+mod test {
+  use std::rc::Rc;
+  use swc_common::FileName;
+  use swc_common::SourceMap;
+  use swc_ecmascript::ast::Module;
+  use swc_ecmascript::codegen::text_writer::JsWriter;
+  use swc_ecmascript::codegen::Node;
+  use swc_ecmascript::parser::Parser;
+  use swc_ecmascript::parser::StringInput;
+  use swc_ecmascript::parser::Syntax;
+  use swc_ecmascript::parser::TsConfig;
+  use swc_ecmascript::visit::Fold;
+  use swc_ecmascript::visit::FoldWith;
+
+  use super::*;
+
+  #[test]
+  fn test_downlevel_imports_type_only() {
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import type { test } from "./mod.ts";"#,
+      ";",
+    );
+  }
+
+  #[test]
+  fn test_downlevel_imports_specifier_only() {
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import "./mod.ts";"#,
+      r#"await import("./mod.ts");"#,
+    );
+
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import {} from "./mod.ts";"#,
+      r#"await import("./mod.ts");"#,
+    );
+  }
+
+  #[test]
+  fn test_downlevel_imports_default() {
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import mod from "./mod.ts";"#,
+      r#"const { default: mod  } = await import("./mod.ts");"#,
+    );
+  }
+
+  #[test]
+  fn test_downlevel_imports_named() {
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import { A } from "./mod.ts";"#,
+      r#"const { A  } = await import("./mod.ts");"#,
+    );
+
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import { A, B, C  } from "./mod.ts";"#,
+      r#"const { A , B , C  } = await import("./mod.ts");"#,
+    );
+
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import { A as LocalA, B, C as LocalC  } from "./mod.ts";"#,
+      r#"const { A: LocalA , B , C: LocalC  } = await import("./mod.ts");"#,
+    );
+  }
+
+  #[test]
+  fn test_downlevel_imports_namespace() {
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import * as mod from "./mod.ts";"#,
+      r#"const mod = await import("./mod.ts");"#,
+    );
+  }
+
+  #[test]
+  fn test_downlevel_imports_mixed() {
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import myDefault, { A, B as LocalB } from "./mod.ts";"#,
+      r#"const { default: myDefault , A , B: LocalB  } = await import("./mod.ts");"#,
+    );
+
+    test_transform(
+      DownlevelImportsFolder,
+      r#"import myDefault, * as mod from "./mod.ts";"#,
+      r#"const { default: myDefault  } = await import("./mod.ts"), mod = await import("./mod.ts");"#,
+    );
+  }
+
+  fn test_transform(
+    mut transform: impl Fold,
+    src: &str,
+    expected_output: &str,
+  ) {
+    let (source_map, module) = parse(src);
+    let output = print(source_map, module.fold_with(&mut transform));
+    assert_eq!(output, format!("{}\n", expected_output));
+  }
+
+  fn parse(src: &str) -> (Rc<SourceMap>, Module) {
+    let source_map = Rc::new(SourceMap::default());
+    let source_file = source_map.new_source_file(
+      FileName::Custom("file.ts".to_string()),
+      src.to_string(),
+    );
+    let input = StringInput::from(&*source_file);
+    let syntax = Syntax::Typescript(TsConfig {
+      ..Default::default()
+    });
+    let mut parser = Parser::new(syntax, input, None);
+    (source_map, parser.parse_module().unwrap())
+  }
+
+  fn print(source_map: Rc<SourceMap>, module: Module) -> String {
+    let mut buf = vec![];
+    {
+      let writer =
+        Box::new(JsWriter::new(source_map.clone(), "\n", &mut buf, None));
+      let config = swc_ecmascript::codegen::Config { minify: false };
+      let mut emitter = swc_ecmascript::codegen::Emitter {
+        cfg: config,
+        comments: None,
+        cm: source_map,
+        wr: writer,
+      };
+      module.emit_with(&mut emitter).unwrap();
+    }
+    String::from_utf8(buf).unwrap()
+  }
+}