feat(transformer/typescript): correct elide imports/exports statements (#2995)

remove ts annotations one benefit: `IdentifierReference` only used on js
code

The `TypescriptReferenceCollector` implementation is inspired by
5f75019683/crates/swc_ecma_transforms_typescript/src/strip_import_export.rs (L9-L99)

This seems simpler to implement than using scope

crates/oxc_transformer/src/lib.rs

@@ -143,8 +143,6 @@ impl<'a> VisitMut<'a> for Transformer<'a> {
     }
 
     fn visit_import_declaration(&mut self, decl: &mut ImportDeclaration<'a>) {
-        self.x0_typescript.transform_import_declaration(decl);
-
         walk_mut::walk_import_declaration_mut(self, decl);
     }
 
@@ -198,4 +196,14 @@ impl<'a> VisitMut<'a> for Transformer<'a> {
 
         walk_mut::walk_variable_declarator_mut(self, declarator);
     }
+
+    fn visit_identifier_reference(&mut self, ident: &mut IdentifierReference<'a>) {
+        self.x0_typescript.transform_identifier_reference(ident);
+        walk_mut::walk_identifier_reference_mut(self, ident);
+    }
+
+    fn visit_statement(&mut self, stmt: &mut Statement<'a>) {
+        self.x0_typescript.transform_statement(stmt);
+        walk_mut::walk_statement_mut(self, stmt);
+    }
 }

crates/oxc_transformer/src/typescript/annotations.rs

@@ -11,25 +11,17 @@ use oxc_span::{Atom, SPAN};
 use oxc_syntax::operator::AssignmentOperator;
 use rustc_hash::FxHashSet;
 
+use super::collector::TypeScriptReferenceCollector;
+
 pub struct TypeScriptAnnotations<'a> {
     #[allow(dead_code)]
     options: Rc<TypeScriptOptions>,
     ctx: Ctx<'a>,
-
-    global_types: FxHashSet<String>,
 }
 
 impl<'a> TypeScriptAnnotations<'a> {
     pub fn new(options: &Rc<TypeScriptOptions>, ctx: &Ctx<'a>) -> Self {
-        Self {
-            options: Rc::clone(options),
-            ctx: Rc::clone(ctx),
-            global_types: FxHashSet::default(),
-        }
-    }
-
-    pub fn is_global_type(&self) -> bool {
-        self.global_types.contains("TODO")
+        Self { options: Rc::clone(options), ctx: Rc::clone(ctx) }
     }
 
     // Convert `export = expr` into `module.exports = expr`
@@ -73,57 +65,113 @@ impl<'a> TypeScriptAnnotations<'a> {
     }
 
     // Remove type only imports/exports
-    pub fn transform_program_on_exit(&self, program: &mut Program<'a>) {
+    pub fn transform_program_on_exit(
+        &self,
+        program: &mut Program<'a>,
+        references: &TypeScriptReferenceCollector,
+    ) {
+        let mut import_type_names = FxHashSet::default();
         let mut module_count = 0;
+        let mut removed_count = 0;
 
-        let body =
-            self.ctx.ast.move_statement_vec(&mut program.body).into_iter().filter_map(|stmt| {
-                // If an import/export declaration, remove all that are type-only
-                if let Statement::ModuleDeclaration(decl) = &stmt {
-                    let keep = match &**decl {
-                        ModuleDeclaration::ImportDeclaration(inner) => !inner.import_kind.is_type(),
-                        ModuleDeclaration::ExportAllDeclaration(inner) => {
-                            !inner.is_typescript_syntax()
-                        }
-                        ModuleDeclaration::ExportNamedDeclaration(inner) => {
-                            !(inner.is_typescript_syntax()
-                                || inner.specifiers.is_empty()
-                                || inner.specifiers.iter().all(|spec| spec.export_kind.is_type())
-                                || self.is_global_type())
-                        }
-                        ModuleDeclaration::ExportDefaultDeclaration(inner) => {
-                            !inner.is_typescript_syntax()
-                        }
-                        ModuleDeclaration::TSNamespaceExportDeclaration(_) => false,
+        program.body.retain_mut(|stmt| {
+            let Statement::ModuleDeclaration(module_decl) = stmt else {
+                return true;
+            };
 
-                        // Replace with `module.exports = expr`
-                        ModuleDeclaration::TSExportAssignment(exp) => {
-                            return Some(self.create_module_exports(exp));
-                        }
-                    };
+            let need_delete = match &mut **module_decl {
+                ModuleDeclaration::ExportNamedDeclaration(decl) => {
+                    decl.specifiers.retain(|specifier| {
+                        !(specifier.export_kind.is_type()
+                            || import_type_names.contains(specifier.exported.name()))
+                    });
 
-                    if keep {
-                        module_count += 1;
-                    } else {
-                        return None;
-                    }
+                    decl.export_kind.is_type()
+                        || ((decl.declaration.is_none()
+                            || decl.declaration.as_ref().is_some_and(|d| {
+                                d.modifiers().is_some_and(|modifiers| {
+                                    modifiers.contains(ModifierKind::Declare)
+                                }) || matches!(
+                                    d,
+                                    Declaration::TSInterfaceDeclaration(_)
+                                        | Declaration::TSTypeAliasDeclaration(_)
+                                )
+                            }))
+                            && decl.specifiers.is_empty())
                 }
+                ModuleDeclaration::ImportDeclaration(decl) => {
+                    let is_type = decl.import_kind.is_type();
 
-                Some(stmt)
-            });
+                    let is_specifiers_empty =
+                        decl.specifiers.as_ref().is_some_and(|s| s.is_empty());
 
-        program.body = self.ctx.ast.new_vec_from_iter(body);
+                    if let Some(specifiers) = &mut decl.specifiers {
+                        specifiers.retain(|specifier| match specifier {
+                            ImportDeclarationSpecifier::ImportSpecifier(s) => {
+                                if is_type || s.import_kind.is_type() {
+                                    import_type_names.insert(s.local.name.clone());
+                                    return false;
+                                }
+
+                                if self.options.only_remove_type_imports {
+                                    return true;
+                                }
+
+                                references.has_reference(&s.local.name)
+                            }
+                            ImportDeclarationSpecifier::ImportDefaultSpecifier(s) => {
+                                if is_type {
+                                    import_type_names.insert(s.local.name.clone());
+                                    return false;
+                                }
+
+                                if self.options.only_remove_type_imports {
+                                    return true;
+                                }
+                                references.has_reference(&s.local.name)
+                            }
+                            ImportDeclarationSpecifier::ImportNamespaceSpecifier(s) => {
+                                if is_type {
+                                    import_type_names.insert(s.local.name.clone());
+                                }
+
+                                if self.options.only_remove_type_imports {
+                                    return true;
+                                }
+
+                                references.has_reference(&s.local.name)
+                            }
+                        });
+                    }
+
+                    decl.import_kind.is_type()
+                        || (!self.options.only_remove_type_imports
+                            && !is_specifiers_empty
+                            && decl
+                                .specifiers
+                                .as_ref()
+                                .is_some_and(|specifiers| specifiers.is_empty()))
+                }
+                _ => false,
+            };
+
+            if need_delete {
+                removed_count += 1;
+            } else {
+                module_count += 1;
+            }
+
+            !need_delete
+        });
 
         // Determine if we still have import/export statements, otherwise we
         // need to inject an empty statement (`export {}`) so that the file is
         // still considered a module
-        if module_count == 0 && self.ctx.semantic.source_type().is_module() {
-            // FIXME
-            // program.body.push(self.ctx.ast.module_declaration(
-            // ModuleDeclaration::ExportNamedDeclaration(
-            // self.ctx.ast.plain_export_named_declaration(SPAN, self.ctx.ast.new_vec(), None),
-            // ),
-            // ));
+        if module_count == 0 && removed_count > 0 {
+            let export_decl = ModuleDeclaration::ExportNamedDeclaration(
+                self.ctx.ast.plain_export_named_declaration(SPAN, self.ctx.ast.new_vec(), None),
+            );
+            program.body.push(self.ctx.ast.module_declaration(export_decl));
         }
     }
 
@@ -172,11 +220,6 @@ impl<'a> TypeScriptAnnotations<'a> {
         });
     }
 
-    pub fn transform_export_named_declaration(&mut self, decl: &mut ExportNamedDeclaration<'a>) {
-        // Remove type only specifiers
-        decl.specifiers.retain(|spec| !spec.export_kind.is_type());
-    }
-
     pub fn transform_expression(&mut self, expr: &mut Expression<'a>) {
         *expr = self.ctx.ast.copy(expr.get_inner_expression());
     }
@@ -196,16 +239,6 @@ impl<'a> TypeScriptAnnotations<'a> {
         func.modifiers.remove_type_modifiers();
     }
 
-    pub fn transform_import_declaration(&mut self, decl: &mut ImportDeclaration<'a>) {
-        // Remove type only specifiers
-        if let Some(specifiers) = &mut decl.specifiers {
-            specifiers.retain(|spec| match spec {
-                ImportDeclarationSpecifier::ImportSpecifier(inner) => !inner.import_kind.is_type(),
-                _ => true,
-            });
-        }
-    }
-
     pub fn transform_jsx_opening_element(&mut self, elem: &mut JSXOpeningElement<'a>) {
         elem.type_parameters = None;
     }
@@ -284,4 +317,12 @@ impl<'a> TypeScriptAnnotations<'a> {
     ) {
         expr.type_parameters = None;
     }
+
+    pub fn transform_statement(&mut self, decl: &mut Statement<'a>) {
+        if let Statement::ModuleDeclaration(module_decl) = decl {
+            if let ModuleDeclaration::TSExportAssignment(exp) = &mut **module_decl {
+                *decl = self.create_module_exports(exp);
+            }
+        }
+    }
 }

crates/oxc_transformer/src/typescript/collector.rs

@@ -0,0 +1,36 @@
+use oxc_ast::ast::{ExportNamedDeclaration, IdentifierReference};
+use oxc_span::Atom;
+use rustc_hash::FxHashSet;
+
+/// Collects identifier references
+/// Indicates whether the BindingIdentifier is referenced or used in the ExportNamedDeclaration
+#[derive(Debug)]
+pub struct TypeScriptReferenceCollector<'a> {
+    names: FxHashSet<Atom<'a>>,
+}
+
+impl<'a> TypeScriptReferenceCollector<'a> {
+    pub fn new() -> Self {
+        Self { names: FxHashSet::default() }
+    }
+
+    pub fn has_reference(&self, name: &Atom) -> bool {
+        self.names.contains(name)
+    }
+
+    pub fn visit_identifier_reference(&mut self, ident: &IdentifierReference<'a>) {
+        self.names.insert(ident.name.clone());
+    }
+
+    pub fn visit_transform_export_named_declaration(&mut self, decl: &ExportNamedDeclaration<'a>) {
+        if decl.export_kind.is_type() {
+            return;
+        }
+
+        for specifier in &decl.specifiers {
+            if specifier.export_kind.is_value() {
+                self.names.insert(specifier.local.name().clone());
+            }
+        }
+    }
+}

crates/oxc_transformer/src/typescript/mod.rs

@@ -1,4 +1,5 @@
 mod annotations;
+mod collector;
 mod namespace;
 
 use std::rc::Rc;
@@ -10,11 +11,15 @@ use oxc_ast::ast::*;
 
 use crate::context::Ctx;
 
-use self::annotations::TypeScriptAnnotations;
+use self::{annotations::TypeScriptAnnotations, collector::TypeScriptReferenceCollector};
 
 #[derive(Debug, Default, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
-pub struct TypeScriptOptions;
+pub struct TypeScriptOptions {
+    /// When set to true, the transform will only remove type-only imports (introduced in TypeScript 3.8).
+    /// This should only be used if you are using TypeScript >= 3.8.
+    only_remove_type_imports: bool,
+}
 
 /// [Preset TypeScript](https://babeljs.io/docs/babel-preset-typescript)
 ///
@@ -43,6 +48,7 @@ pub struct TypeScript<'a> {
     ctx: Ctx<'a>,
 
     annotations: TypeScriptAnnotations<'a>,
+    reference_collector: TypeScriptReferenceCollector<'a>,
 }
 
 impl<'a> TypeScript<'a> {
@@ -51,6 +57,7 @@ impl<'a> TypeScript<'a> {
 
         Self {
             annotations: TypeScriptAnnotations::new(&options, ctx),
+            reference_collector: TypeScriptReferenceCollector::new(),
             options,
             ctx: Rc::clone(ctx),
         }
@@ -60,7 +67,7 @@ impl<'a> TypeScript<'a> {
 // Transforms
 impl<'a> TypeScript<'a> {
     pub fn transform_program_on_exit(&self, program: &mut Program<'a>) {
-        self.annotations.transform_program_on_exit(program);
+        self.annotations.transform_program_on_exit(program, &self.reference_collector);
     }
 
     pub fn transform_arrow_expression(&mut self, expr: &mut ArrowFunctionExpression<'a>) {
@@ -84,7 +91,7 @@ impl<'a> TypeScript<'a> {
     }
 
     pub fn transform_export_named_declaration(&mut self, decl: &mut ExportNamedDeclaration<'a>) {
-        self.annotations.transform_export_named_declaration(decl);
+        self.reference_collector.visit_transform_export_named_declaration(decl);
     }
 
     pub fn transform_expression(&mut self, expr: &mut Expression<'a>) {
@@ -103,10 +110,6 @@ impl<'a> TypeScript<'a> {
         self.annotations.transform_function(func, flags);
     }
 
-    pub fn transform_import_declaration(&mut self, decl: &mut ImportDeclaration<'a>) {
-        self.annotations.transform_import_declaration(decl);
-    }
-
     pub fn transform_jsx_opening_element(&mut self, elem: &mut JSXOpeningElement<'a>) {
         self.annotations.transform_jsx_opening_element(elem);
     }
@@ -137,4 +140,12 @@ impl<'a> TypeScript<'a> {
     ) {
         self.annotations.transform_tagged_template_expression(expr);
     }
+
+    pub fn transform_identifier_reference(&mut self, ident: &mut IdentifierReference<'a>) {
+        self.reference_collector.visit_identifier_reference(ident);
+    }
+
+    pub fn transform_statement(&mut self, stmt: &mut Statement<'a>) {
+        self.annotations.transform_statement(stmt);
+    }
 }

tasks/transform_conformance/babel.snap.md

@@ -1,4 +1,4 @@
-Passed: 93/227
+Passed: 123/227
 
 # All Passed:
 * babel-plugin-transform-react-jsx-source
@@ -24,7 +24,7 @@ Passed: 93/227
 * opts/optimizeConstEnums/input.ts
 * opts/rewriteImportExtensions/input.ts
 
-# babel-plugin-transform-typescript (49/147)
+# babel-plugin-transform-typescript (79/147)
 * class/abstract-allowDeclareFields-false/input.ts
 * class/abstract-allowDeclareFields-true/input.ts
 * class/abstract-class-decorated/input.ts
@@ -40,48 +40,18 @@ Passed: 93/227
 * class/private-method-override-transform-private/input.ts
 * class/transform-properties-declare-wrong-order/input.ts
 * declarations/erased/input.ts
-* declarations/export-declare-enum/input.ts
 * declarations/nested-namespace/input.mjs
-* exports/declare-namespace/input.ts
 * exports/declare-shadowed/input.ts
 * exports/declared-types/input.ts
 * exports/export-const-enums/input.ts
-* exports/export-type/input.ts
-* exports/export-type-from/input.ts
 * exports/export-type-star-from/input.ts
 * exports/export=/input.ts
-* exports/imported-types/input.ts
-* exports/imported-types-only-remove-type-imports/input.ts
-* exports/issue-9916-3/input.ts
-* exports/simple/input.ts
-* exports/type-only-export-specifier-1/input.ts
-* exports/type-only-export-specifier-2/input.ts
 * function/overloads-exports/input.mjs
-* imports/elide-preact/input.ts
-* imports/elide-react/input.ts
 * imports/elide-type-referenced-in-imports-equal-no/input.ts
-* imports/elide-typeof/input.ts
-* imports/elision/input.ts
-* imports/elision-export-type/input.ts
-* imports/elision-locations/input.ts
-* imports/elision-qualifiedname/input.ts
-* imports/elision-rename/input.ts
 * imports/enum-id/input.ts
 * imports/enum-value/input.ts
-* imports/import-named-type/input.ts
-* imports/import-named-type-default-and-named/input.ts
-* imports/import-removed-exceptions/input.ts
-* imports/import-type/input.ts
-* imports/import-type-func-with-duplicate-name/input.ts
-* imports/import-type-not-removed/input.ts
 * imports/import=-module/input.ts
-* imports/only-remove-type-imports/input.ts
-* imports/property-signature/input.ts
-* imports/type-only-export-specifier-1/input.ts
 * imports/type-only-export-specifier-2/input.ts
-* imports/type-only-import-specifier-2/input.ts
-* imports/type-only-import-specifier-3/input.ts
-* imports/type-only-import-specifier-4/input.ts
 * namespace/alias/input.ts
 * namespace/ambient-module-nested/input.ts
 * namespace/ambient-module-nested-exported/input.ts