Don't instrument code if not necessary

lib/init/eval.js

@@ -148,7 +148,10 @@ function evalIndirect(code, fileProps, tracker) {
 	// No need to wrap eval code in a further `eval()` call the way there is for direct eval with
 	// prefix change, because any local declaration of a var called `eval` will be renamed.
 	// So `eval` in injected statement will always refer to `global.eval`.
+	let codeWasInstrumented = false;
 	const addInternalVarsToAst = (ast, {internalVarsPrefixNum: insidePrefixNum}) => {
+		codeWasInstrumented = true;
+
 		ast.program.body.unshift(
 			t.variableDeclaration('const', [t.variableDeclarator(
 				t.arrayPattern([trackerVarNode(insidePrefixNum), getScopeIdVarNode(insidePrefixNum)]),
@@ -162,10 +165,12 @@ function evalIndirect(code, fileProps, tracker) {
 	// 1. Array containing `tracker` and `getScopeId` functions
 	//    - for `const [livepack_tracker, livepack_getScopeId] = eval;`.
 	// 2. Revert to returning the usual shimmed `eval`.
-	getEval = () => {
-		getEval = getShimmedEval;
-		return [tracker, getScopeId];
-	};
+	if (codeWasInstrumented) {
+		getEval = () => {
+			getEval = getShimmedEval;
+			return [tracker, getScopeId];
+		};
+	}
 
 	// `eval()` code without external scope
 	return nativeEval(code);
@@ -270,6 +275,7 @@ function evalDirect(
 	// const livepack1_tracker = livepack_tracker.createTracker(1),
 	//   livepack1_getScopeId = livepack_getScopeId;
 	// ```
+	// Also create var for `livepack_localEval` if required.
 	// The additional wrapping in another `eval()` is in case this code defines a var which clashes
 	// with the external `livepack_tracker` or `livepack_getScopeId` var.
 	let prefixNumIsChanged = false;
@@ -413,15 +419,19 @@ function compile(code, fileProps, state, isStrict, outsidePrefixNum, addInternal
 	modifyAst(ast, filename, false, isStrict, undefined, state);
 	const instrumentationState = state.state;
 
-	// Update next block ID for file
-	fileProps.nextBlockId = instrumentationState.nextBlockId;
+	// Only substitute instrumented code if instrumentation is necessary.
+	// Plain calculation e.g. `x + 2` doesn't require instrumentation.
+	if (instrumentationState.fileContainsFunctionsOrEval) {
+		// Update next block ID for file
+		fileProps.nextBlockId = instrumentationState.nextBlockId;
 
-	// If indirect `eval`, or direct `eval()` with different prefix nums inside and outside `eval()`,
-	// inject `livepack_tracker` and `livepack_getScopeId`
-	addInternalVarsToAst(ast, instrumentationState);
+		// If indirect `eval`, or direct `eval()` with different prefix nums inside and outside `eval()`,
+		// inject `livepack_tracker` and `livepack_getScopeId`
+		addInternalVarsToAst(ast, instrumentationState);
 
-	// Return instrumented code
-	code = generateCode(ast); // eslint-disable-line no-use-before-define
+		// Generate instrumented code
+		code = generateCode(ast); // eslint-disable-line no-use-before-define
+	}
 
 	if (DEBUG) {
 		/* eslint-disable no-console */