fix(es/typescript): Handle single type statement in if/for/while (#9364)

- Closes: #9363

Author: magic-akari

.changeset/lucky-panthers-cough.md

@@ -0,0 +1,6 @@
+---
+swc_ecma_transforms_typescript: patch
+swc_fast_ts_strip: patch
+---
+
+Fix (TypeScript): Handle single type statement in if/for/while

crates/swc_ecma_transforms_typescript/src/strip_type.rs

@@ -205,8 +205,16 @@ impl VisitMut for StripType {
     }
 
     fn visit_mut_stmts(&mut self, n: &mut Vec<Stmt>) {
-        n.retain(should_retain_stmt);
         n.visit_mut_children_with(self);
+        n.retain(|s| !s.is_empty());
+    }
+
+    fn visit_mut_stmt(&mut self, n: &mut Stmt) {
+        if should_retain_stmt(n) {
+            n.visit_mut_children_with(self);
+        } else if !n.is_empty() {
+            n.take();
+        }
     }
 
     fn visit_mut_ts_import_equals_decl(&mut self, _: &mut TsImportEqualsDecl) {

crates/swc_fast_ts_strip/src/lib.rs

@@ -11,12 +11,13 @@ use swc_common::{
     BytePos, FileName, Mark, SourceMap, Span, Spanned,
 };
 use swc_ecma_ast::{
-    ArrowExpr, BindingIdent, Class, ClassDecl, ClassMethod, ClassProp, EsVersion, ExportAll,
-    ExportDecl, ExportSpecifier, FnDecl, ImportDecl, ImportSpecifier, NamedExport, Param, Pat,
-    Program, TsAsExpr, TsConstAssertion, TsEnumDecl, TsExportAssignment, TsImportEqualsDecl,
-    TsIndexSignature, TsInstantiation, TsInterfaceDecl, TsModuleDecl, TsModuleName,
-    TsNamespaceDecl, TsNonNullExpr, TsParamPropParam, TsSatisfiesExpr, TsTypeAliasDecl, TsTypeAnn,
-    TsTypeAssertion, TsTypeParamDecl, TsTypeParamInstantiation, VarDecl,
+    ArrowExpr, BindingIdent, Class, ClassDecl, ClassMethod, ClassProp, Decl, DoWhileStmt,
+    EsVersion, ExportAll, ExportDecl, ExportSpecifier, FnDecl, ForInStmt, ForOfStmt, ForStmt,
+    IfStmt, ImportDecl, ImportSpecifier, NamedExport, Param, Pat, Program, Stmt, TsAsExpr,
+    TsConstAssertion, TsEnumDecl, TsExportAssignment, TsImportEqualsDecl, TsIndexSignature,
+    TsInstantiation, TsInterfaceDecl, TsModuleDecl, TsModuleName, TsNamespaceDecl, TsNonNullExpr,
+    TsParamPropParam, TsSatisfiesExpr, TsTypeAliasDecl, TsTypeAnn, TsTypeAssertion,
+    TsTypeParamDecl, TsTypeParamInstantiation, VarDecl, WhileStmt,
 };
 use swc_ecma_parser::{
     lexer::Lexer,
@@ -910,8 +911,76 @@ impl Visit for TsStrip {
 
         n.visit_children_with(self);
     }
+
+    fn visit_if_stmt(&mut self, n: &IfStmt) {
+        n.visit_children_with(self);
+
+        if n.cons.is_ts_stmt() {
+            self.add_overwrite(n.cons.span_lo(), b';');
+        }
+
+        if let Some(alt) = &n.alt {
+            if alt.is_ts_stmt() {
+                self.add_overwrite(alt.span_lo(), b';');
+            }
+        }
+    }
+
+    fn visit_for_stmt(&mut self, n: &ForStmt) {
+        n.visit_children_with(self);
+
+        if n.body.is_ts_stmt() {
+            self.add_overwrite(n.body.span_lo(), b';');
+        }
+    }
+
+    fn visit_for_in_stmt(&mut self, n: &ForInStmt) {
+        n.visit_children_with(self);
+
+        if n.body.is_ts_stmt() {
+            self.add_overwrite(n.body.span_lo(), b';');
+        }
+    }
+
+    fn visit_for_of_stmt(&mut self, n: &ForOfStmt) {
+        n.visit_children_with(self);
+
+        if n.body.is_ts_stmt() {
+            self.add_overwrite(n.body.span_lo(), b';');
+        }
+    }
+
+    fn visit_while_stmt(&mut self, n: &WhileStmt) {
+        n.visit_children_with(self);
+
+        if n.body.is_ts_stmt() {
+            self.add_overwrite(n.body.span_lo(), b';');
+        }
+    }
+
+    fn visit_do_while_stmt(&mut self, n: &DoWhileStmt) {
+        n.visit_children_with(self);
+
+        if n.body.is_ts_stmt() {
+            self.add_overwrite(n.body.span_lo(), b';');
+        }
+    }
 }
 
+trait IsTsStmt {
+    fn is_ts_stmt(&self) -> bool;
+}
+
+impl IsTsStmt for Stmt {
+    fn is_ts_stmt(&self) -> bool {
+        match self {
+            Stmt::Decl(Decl::TsInterface { .. } | Decl::TsTypeAlias(..)) => true,
+            Stmt::Decl(Decl::TsModule(n)) => n.declare || matches!(n.id, TsModuleName::Str(..)),
+            Stmt::Decl(Decl::TsEnum(e)) => e.declare,
+            _ => false,
+        }
+    }
+}
 trait U8Helper {
     fn is_utf8_char_boundary(&self) -> bool;
 }

crates/swc_fast_ts_strip/tests/fixture/single-ts-stmt.js

@@ -0,0 +1,22 @@
+if (false) ;                
+console.log("Hello, World!");
+
+if (false) { }
+else ;                
+console.log("Hello, World!");
+
+for (; false;)
+    ;              
+console.log("Hello, World!");
+
+for (; false;)
+    ;              
+console.log("Hello, World!");
+
+while (false)
+    ;                
+console.log("Hello, World!");
+
+do
+    ;              
+while (false);

crates/swc_fast_ts_strip/tests/fixture/single-ts-stmt.transform.js

@@ -0,0 +1,12 @@
+if (false) ;
+console.log("Hello, World!");
+if (false) {} else ;
+console.log("Hello, World!");
+for(; false;);
+console.log("Hello, World!");
+for(; false;);
+console.log("Hello, World!");
+while(false);
+console.log("Hello, World!");
+do ;
+while (false)

crates/swc_fast_ts_strip/tests/fixture/single-ts-stmt.ts

@@ -0,0 +1,22 @@
+if (false) type Foo = string
+console.log("Hello, World!");
+
+if (false) { }
+else type Bar = string
+console.log("Hello, World!");
+
+for (; false;)
+    interface X { }
+console.log("Hello, World!");
+
+for (; false;)
+    interface X { }
+console.log("Hello, World!");
+
+while (false)
+    type Baz = string
+console.log("Hello, World!");
+
+do
+    interface X { }
+while (false);