Why is rollup creating an additional file of just exports from my entry file?

[twilson90]

My entry file 'app.js' contains a lot of code, dynamic imports, exports, etc.

I can't figure out why Rollup decides to create a file with just the exports from my entry file, named 'app-[hash1].js':

System.register(["./app.js"],(function(a){"use strict";var e;return{setters:[function(t){e=t.q,a({$:t.af,AccountAddress:t.aS,AdWhy:t.b8,AdditionalProductPicker:t.b4,AddressFormModal:t.aU,Animation:t.Q,Awards:t.aR,Banner:t.aN,Cart:t.aw,CartModal:t.ao,ColorPickerInput:t.b2,ColorPickerListInput:t.b1,Component:t.ag,ControlsIntroScreen:t.bc,CountryProvinceSelector:t.ar,CurrencySwitcher:t.ak,CustomerAddresses:t.aT,CustomerLogin:t.bb,Drawer:t.aG,Easing:t.s,EventManager:t.a5,FakeInputComponent:t.aC,FormHelper:t.aX,Hammer:t.H,HammerManagerEx:t.ac,HorizontalScroller:t.aD,IMAGE_WIDTHS:t.x,ImageRevealSlider:t.b6,InputWrapper:t.aB,LineItem:t.au,List:t.be,ListItem:t.aL,LoadMoreDummy:t.bd,LoadingOverlay:t.at,MAX_PRODUCT_IMAGE_SIZE:t.M,MediaAndText:t.b7,MediaGrid:t.aQ,MediaPlaceholder:t.aF,Modal:t.aj,Navigation:t.az,NumericInput:t.aA,PARALLAX_MAX:t.P,Pagination:t.av,PaginationAndParameters:t.bf,PendantAd:t.aO,PopupModal:t.am,Price:t.aH,ProductDimensions:t.b5,ProductFormModal:t.aV,ProductImages:t.a_,ProductTestimonial:t.b0,ProductWrapper:t.aZ,RatingInput:t.b3,ResponsiveImage:t.aE,Reviews:t.b9,ReviewsCarousel:t.ba,RichText:t.ax,SIZES:t.w,SVGPreviewer:t.ae,SelectWrapper:t.aq,ShippingCalculator:t.aW,ShopifyBlock:t.ah,ShopifySection:t.ai,ShopifyUtils:t.S,Slideshow:t.aP,StarRating:t.ap,Sticky:t.ay,StorefrontAPI:t.ad,TabContainer:t.aY,Template:t.aJ,ThumbnailScroller:t.a$,TickerTape:t.as,Timer:t.an,Title:t.al,Validation:t.a4,WatermarkContainer:t.aM,Wishlist:t.aI,WishlistModal:t.aK,animate_element:t.O,breakpoints:t.A,convert_dimensions_to_mm:t.a2,escape:t.a6,get_document_offset:t.$,get_nav_height:t.B,get_nearest_sibling:t.X,get_text_nodes:t.a9,get_window_breakpoint:t.D,graphql_query:t.a7,hide:t.N,html_to_elements:t.W,icon_html:t.a0,init_app:t.bi,is_fullscreen:t.E,load_section:t.a3,loader:t.bg,modify_text:t.aa,open_shopify_chat:t.ab,pulse:t.a8,re_escaped_html:t.y,re_unescaped_html:t.z,reflow:t.U,reset_css_animations:t.V,scroll_into_view:t.Y,show:t.K,sprite_html:t.a1,template:t.bh,tinycolor:t.t,toggle_fullscreen:t.F,toggle_loading:t.J,utils:t.u,validate_form:t.Z})}],execute:function(){a("md5",e.md5)}}}));

And it creates another file 'app-[hash2].js' that contains all the code relating to those exported variables and methods.

I would like it to just produce 1 file for 'app.js' and 1 file for each of its dynamic imports.

I try to recreate this behaviour with minimal code and it will always produce 1 app.js file instead of 2. I'm sure there's a good reason, I just can't figure out why it's doing this for one entry file and not another.

[lukastaegert]

https://rollupjs.org/configuration-options/#preserveentrysignatures will likely provide some help. allow-extension might be the value you need.

[twilson90]

Thanks, I'll check that out.

Before you responded I was in the middle of outlining a minimal example of the issue:

a.js:

import "./b.js";
import("./c.js");
export function a() {}

b.js
console.log("".concat(""));

c.js
console.log([].find(a=>a));

When I compile a.js, I would expect 2 files:
'a.js' - consists of a + b
'c-[hash].js' - consists of c.js

but instead I get:

'a.js' - consists of definitions for a's exported variables
'a-[hash].js - consists of all the code in a.js
'c-[hash].js' - consists of c.js

If I change the contents of b.js to not use String.concat, or c.js to not use Array.find, then it outputs the expected 2 files.

Confusing!

[twilson90]

Well adding preserveEntrySignatures: "allow-extension" appeared to do the trick. Thanks!
Still curious as to the underlying behaviour.

[lukastaegert]

Shared dependencies between entry files and dynamic imports are inlined into the entry chunk. That means, the entry chunk gets an additional export, changing its export signature.

Small example:
https://rollupjs.org/repl/?version=4.12.0&shareable=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