The issue in the rollup/plugin repo: rollup/plugins#1425
The CommonJS plugin in rollup has a bug where it sometimes fails to detect a
circular dependency. The issue that this call to isCyclic
happens before the dependency graph is fully built and so
loadModule(resolved) might be skipped while it shouldn't be.
And then getTypeForFullyAnalyzedModule
here
is called before the module is indeed fully analyzed. Then the module doesn't
get "require wrapper" while it does need one.
The dependency graph between the modules in the repo is like this:
5 <-- 4 <-- 11 <-- 10
| ^ ^
V | |
6 1 <-- main 9
| | ^
V V |
7 --> 2 <=> 3 ----> 8
If the dependency from module3.js to module2.js is removed, then everything
works fine. But as it is, loading index.html fails with TypeError: m4.inc is not a function.
But you don't need to load index.html to observe the issue. Inspect
output/main.js and notice that several modules are not inside a "require
wrapper" while all but main.js and module1.js have a circular dependency on
each other.
Note that the order in which the modules are loaded is not deterministic and depends on when the filesystem responds. It might be possible to reproduce the bug with fewer files but that also makes it more likely that the bug accidentally doesn't happen.