fix #55389: type-unstable join

JuliaLang · Aug 6, 2024 · ac7dab0 · ac7dab0
1 parent 0717a94
commit ac7dab0
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Showing 2 changed files with 7 additions and 1 deletion.
diff --git a/base/strings/io.jl b/base/strings/io.jl
@@ -354,7 +354,8 @@ function join(io::IO, iterator, delim="")
 end
 
 function _join_preserve_annotations(iterator, args...)
-    if isconcretetype(eltype(iterator)) && !_isannotated(eltype(iterator)) && !any(_isannotated, args)
+    et = @default_eltype(iterator)
+    if isconcretetype(et) && !_isannotated(et) && !any(_isannotated, args)
         sprint(join, iterator, args...)
     else
         io = AnnotatedIOBuffer()

diff --git a/test/strings/io.jl b/test/strings/io.jl
@@ -344,3 +344,8 @@ end
 @testset "`string` return types" begin
     @test all(T -> T <: AbstractString, Base.return_types(string))
 end
+
+@testset "type stable `join` (#55389)" begin
+    itr = ("foo" for _ in 1:100)
+    @test Base.return_types(join, (typeof(itr),))[] == String
+end