fix #3416, fix #3425: better enum constant folding

Author: evanw

CHANGELOG.md

@@ -77,6 +77,35 @@
     }
     ```
 
+* Do additional constant folding after cross-module enum inlining ([#3416](https://github.com/evanw/esbuild/issues/3416), [#3425](https://github.com/evanw/esbuild/issues/3425))
+
+    This release adds a few more cases where esbuild does constant folding after cross-module enum inlining.
+
+    ```ts
+    // Original code: enum.ts
+    export enum Platform {
+      WINDOWS = 'windows',
+      MACOS = 'macos',
+      LINUX = 'linux',
+    }
+
+    // Original code: main.ts
+    import { Platform } from './enum';
+    declare const PLATFORM: string;
+    export function logPlatform() {
+      if (PLATFORM == Platform.WINDOWS) console.log('Windows');
+      else if (PLATFORM == Platform.MACOS) console.log('macOS');
+      else if (PLATFORM == Platform.LINUX) console.log('Linux');
+      else console.log('Other');
+    }
+
+    // Old output (with --bundle '--define:PLATFORM="macos"' --minify --format=esm)
+    function n(){"windows"=="macos"?console.log("Windows"):"macos"=="macos"?console.log("macOS"):"linux"=="macos"?console.log("Linux"):console.log("Other")}export{n as logPlatform};
+
+    // New output (with --bundle '--define:PLATFORM="macos"' --minify --format=esm)
+    function n(){console.log("macOS")}export{n as logPlatform};
+    ```
+
 * Formatting support for the `@position-try` rule ([#3773](https://github.com/evanw/esbuild/issues/3773))
 
     Chrome shipped this new CSS at-rule in version 125 as part of the [CSS anchor positioning API](https://developer.chrome.com/blog/anchor-positioning-api). With this release, esbuild now knows to expect a declaration list inside of the `@position-try` body block and will format it appropriately.

internal/bundler_tests/bundler_dce_test.go

@@ -3183,6 +3183,8 @@ func TestCrossModuleConstantFoldingNumber(t *testing.T) {
 					x.a && x.b,
 					x.a || x.b,
 					x.a ?? x.b,
+					x.a ? 'y' : 'n',
+					!x.b ? 'y' : 'n',
 				])
 			`,
 
@@ -3226,6 +3228,8 @@ func TestCrossModuleConstantFoldingNumber(t *testing.T) {
 					a && b,
 					a || b,
 					a ?? b,
+					a ? 'y' : 'n',
+					!b ? 'y' : 'n',
 				])
 			`,
 
@@ -3288,6 +3292,8 @@ func TestCrossModuleConstantFoldingString(t *testing.T) {
 					x.a && x.b,
 					x.a || x.b,
 					x.a ?? x.b,
+					x.a ? 'y' : 'n',
+					!x.b ? 'y' : 'n',
 				])
 			`,
 
@@ -3314,6 +3320,8 @@ func TestCrossModuleConstantFoldingString(t *testing.T) {
 					a && b,
 					a || b,
 					a ?? b,
+					a ? 'y' : 'n',
+					!b ? 'y' : 'n',
 				])
 			`,
 

internal/bundler_tests/snapshots/snapshots_dce.txt

@@ -293,7 +293,9 @@ console.log([
 ], [
   6 /* b */,
   3 /* a */,
-  3 /* a */
+  3 /* a */,
+  "y",
+  "n"
 ]);
 
 ---------- /out/const-entry.js ----------
@@ -331,7 +333,9 @@ console.log([
 ], [
   6,
   3,
-  3
+  3,
+  "y",
+  "n"
 ]);
 
 ---------- /out/nested-entry.js ----------
@@ -361,7 +365,9 @@ console.log([
 ], [
   "bar" /* b */,
   "foo" /* a */,
-  "foo" /* a */
+  "foo" /* a */,
+  "y",
+  "n"
 ]);
 
 ---------- /out/const-entry.js ----------
@@ -385,7 +391,9 @@ console.log([
 ], [
   a && b,
   a || b,
-  a ?? b
+  a ?? b,
+  a ? "y" : "n",
+  b ? "n" : "y"
 ]);
 
 ---------- /out/nested-entry.js ----------

internal/js_printer/js_printer.go

@@ -1749,7 +1749,7 @@ func (p *printer) guardAgainstBehaviorChangeDueToSubstitution(expr js_ast.Expr,
 // module numeric constants and bitwise operations. This is not an general-
 // purpose/optimal approach and never will be. For example, we can't affect
 // tree shaking at this stage because it has already happened.
-func (p *printer) lateConstantFoldUnaryOrBinaryExpr(expr js_ast.Expr) js_ast.Expr {
+func (p *printer) lateConstantFoldUnaryOrBinaryOrIfExpr(expr js_ast.Expr) js_ast.Expr {
 	switch e := expr.Data.(type) {
 	case *js_ast.EImportIdentifier:
 		ref := ast.FollowSymbols(p.symbols, e.Ref)
@@ -1779,7 +1779,7 @@ func (p *printer) lateConstantFoldUnaryOrBinaryExpr(expr js_ast.Expr) js_ast.Exp
 		}
 
 	case *js_ast.EUnary:
-		value := p.lateConstantFoldUnaryOrBinaryExpr(e.Value)
+		value := p.lateConstantFoldUnaryOrBinaryOrIfExpr(e.Value)
 
 		// Only fold again if something chained
 		if value.Data != e.Value.Data {
@@ -1802,8 +1802,8 @@ func (p *printer) lateConstantFoldUnaryOrBinaryExpr(expr js_ast.Expr) js_ast.Exp
 		}
 
 	case *js_ast.EBinary:
-		left := p.lateConstantFoldUnaryOrBinaryExpr(e.Left)
-		right := p.lateConstantFoldUnaryOrBinaryExpr(e.Right)
+		left := p.lateConstantFoldUnaryOrBinaryOrIfExpr(e.Left)
+		right := p.lateConstantFoldUnaryOrBinaryOrIfExpr(e.Right)
 
 		// Only fold again if something changed
 		if left.Data != e.Left.Data || right.Data != e.Right.Data {
@@ -1819,6 +1819,23 @@ func (p *printer) lateConstantFoldUnaryOrBinaryExpr(expr js_ast.Expr) js_ast.Exp
 			// Don't mutate the original AST
 			expr.Data = binary
 		}
+
+	case *js_ast.EIf:
+		test := p.lateConstantFoldUnaryOrBinaryOrIfExpr(e.Test)
+
+		// Only fold again if something changed
+		if test.Data != e.Test.Data {
+			if boolean, sideEffects, ok := js_ast.ToBooleanWithSideEffects(test.Data); ok && sideEffects == js_ast.NoSideEffects {
+				if boolean {
+					return p.lateConstantFoldUnaryOrBinaryOrIfExpr(e.Yes)
+				} else {
+					return p.lateConstantFoldUnaryOrBinaryOrIfExpr(e.No)
+				}
+			}
+
+			// Don't mutate the original AST
+			expr.Data = &js_ast.EIf{Test: test, Yes: e.Yes, No: e.No}
+		}
 	}
 
 	return expr
@@ -1969,7 +1986,7 @@ const (
 	isDeleteTarget
 	isCallTargetOrTemplateTag
 	isPropertyAccessTarget
-	parentWasUnaryOrBinary
+	parentWasUnaryOrBinaryOrIfTest
 )
 
 func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags printExprFlags) {
@@ -1983,10 +2000,10 @@ func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags printExprFla
 	// This sets a flag to avoid doing this when the parent is a unary or binary
 	// operator so that we don't trigger O(n^2) behavior when traversing over a
 	// large expression tree.
-	if p.options.MinifySyntax && (flags&parentWasUnaryOrBinary) == 0 {
+	if p.options.MinifySyntax && (flags&parentWasUnaryOrBinaryOrIfTest) == 0 {
 		switch expr.Data.(type) {
-		case *js_ast.EUnary, *js_ast.EBinary:
-			expr = p.lateConstantFoldUnaryOrBinaryExpr(expr)
+		case *js_ast.EUnary, *js_ast.EBinary, *js_ast.EIf:
+			expr = p.lateConstantFoldUnaryOrBinaryOrIfExpr(expr)
 		}
 	}
 
@@ -2655,7 +2672,7 @@ func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags printExprFla
 			p.print("(")
 			flags &= ^forbidIn
 		}
-		p.printExpr(e.Test, js_ast.LConditional, flags&forbidIn)
+		p.printExpr(e.Test, js_ast.LConditional, (flags&forbidIn)|parentWasUnaryOrBinaryOrIfTest)
 		p.printSpace()
 		p.print("?")
 		if p.options.LineLimit <= 0 || !p.printNewlinePastLineLimit() {
@@ -3141,7 +3158,7 @@ func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags printExprFla
 		}
 
 		if !e.Op.IsPrefix() {
-			p.printExpr(e.Value, js_ast.LPostfix-1, parentWasUnaryOrBinary)
+			p.printExpr(e.Value, js_ast.LPostfix-1, parentWasUnaryOrBinaryOrIfTest)
 		}
 
 		if entry.IsKeyword {
@@ -3162,7 +3179,7 @@ func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags printExprFla
 		}
 
 		if e.Op.IsPrefix() {
-			valueFlags := parentWasUnaryOrBinary
+			valueFlags := parentWasUnaryOrBinaryOrIfTest
 			if e.Op == js_ast.UnOpDelete {
 				valueFlags |= isDeleteTarget
 			}
@@ -3352,9 +3369,9 @@ func (v *binaryExprVisitor) checkAndPrepare(p *printer) bool {
 
 	if e.Op == js_ast.BinOpComma {
 		// The result of the left operand of the comma operator is unused
-		v.leftFlags = (v.flags & forbidIn) | exprResultIsUnused | parentWasUnaryOrBinary
+		v.leftFlags = (v.flags & forbidIn) | exprResultIsUnused | parentWasUnaryOrBinaryOrIfTest
 	} else {
-		v.leftFlags = (v.flags & forbidIn) | parentWasUnaryOrBinary
+		v.leftFlags = (v.flags & forbidIn) | parentWasUnaryOrBinaryOrIfTest
 	}
 	return true
 }
@@ -3382,9 +3399,9 @@ func (v *binaryExprVisitor) visitRightAndFinish(p *printer) {
 
 	if e.Op == js_ast.BinOpComma {
 		// The result of the right operand of the comma operator is unused if the caller doesn't use it
-		p.printExpr(e.Right, v.rightLevel, (v.flags&(forbidIn|exprResultIsUnused))|parentWasUnaryOrBinary)
+		p.printExpr(e.Right, v.rightLevel, (v.flags&(forbidIn|exprResultIsUnused))|parentWasUnaryOrBinaryOrIfTest)
 	} else {
-		p.printExpr(e.Right, v.rightLevel, (v.flags&forbidIn)|parentWasUnaryOrBinary)
+		p.printExpr(e.Right, v.rightLevel, (v.flags&forbidIn)|parentWasUnaryOrBinaryOrIfTest)
 	}
 
 	if v.wrap {