fix: Try harder to construct a use chain in synthetic AST

This should work around a more strict DCE in rollup > 2.75
Swatinem · May 29, 2022 · cbdb276 · cbdb276
1 parent cfdf55a
commit cbdb276
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Showing 4 changed files with 43 additions and 13 deletions.
diff --git a/package-lock.json b/package-lock.json
diff --git a/src/transform/DeclarationScope.ts b/src/transform/DeclarationScope.ts
@@ -6,6 +6,7 @@ import {
   createIdentifier,
   createIIFE,
   createReference,
+  createReturn,
   Range,
   withStartEnd,
 } from "./astHelpers.js";
@@ -37,6 +38,7 @@ interface DeclarationScopeOptions {
 export class DeclarationScope {
   declaration: ESTree.FunctionDeclaration;
   iife?: ESTree.ExpressionStatement;
+  private returnExpr: ESTree.ArrayExpression;
 
   constructor({ id, range }: DeclarationScopeOptions) {
     if (id) {
@@ -46,6 +48,9 @@ export class DeclarationScope {
       this.iife = iife;
       this.declaration = fn as any;
     }
+    const ret = createReturn();
+    this.declaration.body.body.push(ret.stmt);
+    this.returnExpr = ret.expr;
   }
 
   /**
@@ -67,9 +72,6 @@ export class DeclarationScope {
     this.scopes[this.scopes.length - 1]?.add(name);
   }
 
-  pushRaw(expr: ESTree.AssignmentPattern) {
-    this.declaration.params.push(expr);
-  }
   pushReference(id: ESTree.Expression) {
     let name: string | undefined;
     // We convert references from TS AST to ESTree
@@ -90,7 +92,10 @@ export class DeclarationScope {
         }
       }
     }
-    this.pushRaw(createReference(id));
+    const { ident, expr } = createReference(id);
+
+    this.declaration.params.push(expr);
+    this.returnExpr.elements.push(ident);
   }
   pushIdentifierReference(id: ts.Identifier) {
     this.pushReference(createIdentifier(id));

diff --git a/src/transform/astHelpers.ts b/src/transform/astHelpers.ts
@@ -22,14 +22,18 @@ export function createProgram(node: ts.SourceFile): ESTree.Program {
  * Creates a reference to `id`:
  * `_ = ${id}`
  */
-export function createReference(id: ESTree.Expression): ESTree.AssignmentPattern {
+export function createReference(id: ESTree.Expression): { ident: ESTree.Identifier; expr: ESTree.AssignmentPattern } {
+  const ident: ESTree.Identifier = {
+    type: "Identifier",
+    name: String(IDs++),
+  };
   return {
-    type: "AssignmentPattern",
-    left: {
-      type: "Identifier",
-      name: String(IDs++),
+    ident,
+    expr: {
+      type: "AssignmentPattern",
+      left: ident,
+      right: id,
     },
-    right: id,
   };
 }
 
@@ -47,7 +51,7 @@ export function createIdentifier(node: ts.Identifier): ESTree.Identifier {
  * Create a new Scope which is always included
  * `(function (_ = MARKER) {})()`
  */
-export function createIIFE(range: Range) {
+export function createIIFE(range: Range): { fn: ESTree.FunctionExpression; iife: ESTree.ExpressionStatement } {
   const fn = withStartEnd<ESTree.FunctionExpression>(
     {
       type: "FunctionExpression",
@@ -72,6 +76,24 @@ export function createIIFE(range: Range) {
   return { fn, iife };
 }
 
+/**
+ * Create a dummy ReturnStatement with an ArrayExpression:
+ * `return [];`
+ */
+export function createReturn(): { stmt: ESTree.Statement; expr: ESTree.ArrayExpression } {
+  const expr: ESTree.ArrayExpression = {
+    type: "ArrayExpression",
+    elements: [],
+  };
+  return {
+    expr,
+    stmt: {
+      type: "ReturnStatement",
+      argument: expr,
+    },
+  };
+}
+
 /**
  * Create a new Declaration and Scope for `id`:
  * `function ${id}(_ = MARKER) {}`

diff --git a/tests/testcases/type-typeof/index.d.ts b/tests/testcases/type-typeof/index.d.ts
@@ -1,4 +1,3 @@
 interface A {}
 declare const a: A;
 export declare function typeQuery(): typeof a;
-export {};