1555
78%

Ran 03 Jun 2026 11:46AM UTC

Jobs 3

Files 352

Run time 2min

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Committed 03 Jun 2026 03:54AM UTC coverage: 77.782% (+0.8%) from 77.002%

Build # 1555

Build Type

push

buildkite

Committed by

web-flow

Commit Message

Don't rewrap other unioned types in flatten_type_union (#61980)

Fixes #61914, using the suggestion by Opus 4.6. (Thanks to @JeffBezanson
for confirmation that the original issue was real)

Here's a simpler example I used to understand the problem:
```
T = TypeVar(:T)
a = UnionAll(T, Union{Vector{T}, Int64})
```

Now, when we do `Union{a, T}`, we get `Union{Int64, Vector, T}` like
expected, since the `T` on the RHS is not bound by the UnionAll, and the
UnionAll of Union was rewritten to Union of UnionAll, leaving us with
`UnionAll(T, Vector{T}) == Vector`.

`Union{T, a}` gave us the wrong answer because `flatten_type_union`,
when doing the UnionAll of Union transform, would re-wrap every Union
component from the beginning of the `out` with the UnionAll's variable,
even if those components were not originally under the UnionAll. The
`out` array would go from `T, Vector{T}, Int64` to `UnionAll(T, T) =>
Any, UnionAll(T, Vector{T}) => Vector, UnionAll(T, Int64) => Int64`,
leaving us with `Any`.

Coverage Stats

65843 of 84651 relevant lines covered (77.78%)

22879463.34 hits per line

Coverage Regressions

Lines	Coverage	∆	File
321	83.98	-0.25%	Compiler/src/abstractinterpretation.jl
217	75.71	-0.31%	Compiler/src/ssair/passes.jl
132	76.88	-0.01%	Compiler/src/optimize.jl
104	78.29	0.23%	base/loading.jl
79	38.85	0.0%	base/version.jl
45	90.89	0.0%	base/iterators.jl
8	24.53	-5.03%	base/special/log.jl
8	66.15	-1.97%	stdlib/Sockets/src/Sockets.jl
3	77.12	3.16%	base/show.jl
1	63.61	0.1%	base/errorshow.jl
1	90.72	-0.23%	base/iobuffer.jl
1	83.21	3.28%	base/stream.jl
1	73.72	-0.05%	Compiler/src/tfuncs.jl

Jobs

ID	Job ID	Ran	Files	Coverage
1555	windows-coverage - 1555	03 Jun 2026 03:10PM UTC	318	76.44
1555	linux-coverage - 1555	03 Jun 2026 02:36PM UTC	351	76.46
1555	macos-coverage - 1555	03 Jun 2026 11:46AM UTC	352	76.49

JuliaLang / julia / 1555
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