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Externs inference: Consider inheritance

Description

If a JavaScript type is inferred, "base" properties are not considered. A specific example is js/document, which gets inferred as js/HTMLDocument. If code makes use of any of the base properties, then an inference warning will get triggered, even though :advanced compilation is fine.

src/test/infer.cljs

1 2 3 4 5 (ns test.infer) (set! *warn-on-infer* true) (.-documentElement js/document)
1 2 $ clj -m cljs.main -co '{:infer-externs true}' -c test.infer WARNING: Cannot resolve property documentElement for inferred type js/HTMLDocument in expression (. js/document -documentElement) at line 5 /Users/mfikes/Desktop/test-infer/src/test/infer.cljs

If you add -O advanced you can confirm that documentElement survives into the compiled artifact without being mangled.

Also, you can work around the issue by hinting the target as being the base type:

1 (.-documentElement ^js/Document js/document)

Perhaps there is some way to make use of the "extends" metadata in the externs in cases like these to check base types before emitting a warning (or by inferring the base type based on the property being accessed). Here is the extends metadata of interest in the example above: https://github.com/google/closure-compiler/blob/50713dceb16b369f8f317e5b49e8a9dec2b47496/externs/browser/w3c_dom2.js#L171

Environment

None

Status

Assignee

Unassigned

Reporter

Mike Fikes

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Approval

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Patch

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Priority

Major