mark side-effects later, to avoid late declarations breaking stuff

src/Module.js

@@ -439,7 +439,7 @@ export default class Module {
 
 	markAllSideEffects () {
 		this.statements.forEach( statement => {
-			if ( statement.hasSideEffects ) statement.mark();
+			statement.markSideEffect();
 		});
 	}
 

src/Statement.js

@@ -52,7 +52,6 @@ export default class Statement {
 		this.dependantIds = [];
 		this.namespaceReplacements = [];
 
-		this.hasSideEffects = false;
 		this.isIncluded = false;
 
 		this.isImportDeclaration = node.type === 'ImportDeclaration';
@@ -173,19 +172,6 @@ export default class Statement {
 					if ( isFunctionDeclaration( node, parent ) ) writeDepth += 1;
 					if ( /Function/.test( node.type ) && !isIife( node, parent ) ) readDepth += 1;
 
-					// If this is a top-level call expression, or an assignment to a global,
-					// this statement will need to be marked
-					if ( !readDepth ) {
-						if ( node.type === 'CallExpression' ) {
-							this.hasSideEffects = true;
-						} else if ( node.type in modifierNodes ) {
-							let subject = node[ modifierNodes[ node.type ] ];
-							while ( subject.type === 'MemberExpression' ) subject = subject.object;
-
-							if ( !this.module.locals.defines( subject.name ) ) this.hasSideEffects = true;
-						}
-					}
-
 					if ( node._scope ) scope = node._scope;
 
 					this.checkForReads( scope, node, parent, !readDepth );
@@ -411,6 +397,29 @@ export default class Statement {
 		});
 	}
 
+	markSideEffect () {
+		const statement = this;
+
+		walk( this.node, {
+			enter ( node, parent ) {
+				if ( /Function/.test( node.type ) && !isIife( node, parent ) ) return this.skip();
+
+				// If this is a top-level call expression, or an assignment to a global,
+				// this statement will need to be marked
+				if ( node.type === 'CallExpression' ) {
+					statement.mark();
+				}
+
+				else if ( node.type in modifierNodes ) {
+					let subject = node[ modifierNodes[ node.type ] ];
+					while ( subject.type === 'MemberExpression' ) subject = subject.object;
+
+					if ( statement.module.bundle.globals.defines( subject.name ) ) statement.mark();
+				}
+			}
+		});
+	}
+
 	replaceIdentifiers ( magicString, names, bundleExports ) {
 		const statement = this;
 

test/form/unused-side-effect/foo.js

@@ -3,4 +3,11 @@ uid = 1;
 uid += 1;
 uid++;
 
+// ensure identifiers aren't treated as globals just because
+// var declaration hasn't been encountered yet...
+uid2 = 1;
+uid2 += 1;
+uid2++;
+var uid2;
+
 export var foo = 42;