make typejoin nothrow (#58578)

Fixes #50985

Author: vtjnash

base/promotion.jl

@@ -23,11 +23,16 @@ typejoin(@nospecialize(t), @nospecialize(s), @nospecialize(u)) = (@_foldable_met
 typejoin(@nospecialize(t), @nospecialize(s), @nospecialize(u), ts...) = (@_foldable_meta; @_nospecializeinfer_meta; afoldl(typejoin, typejoin(t, s, u), ts...))
 function typejoin(@nospecialize(a), @nospecialize(b))
     @_foldable_meta
+    @_nothrow_meta
     @_nospecializeinfer_meta
     if isa(a, TypeVar)
         return typejoin(a.ub, b)
     elseif isa(b, TypeVar)
         return typejoin(a, b.ub)
+    elseif a === b
+        return a
+    elseif !isa(a, Type) || !isa(b, Type)
+        return Any
     elseif a <: b
         return b
     elseif b <: a

test/core.jl

@@ -309,22 +309,9 @@ end  |> only == Type{typejoin(Int, UInt)}
     typejoin(Int, UInt, Float64)
 end  |> only == Type{typejoin(Int, UInt, Float64)}
 
-let res = @test_throws TypeError let
-        Base.Experimental.@force_compile
-        typejoin(1, 2)
-        nothing
-    end
-    err = res.value
-    @test err.func === :<:
-end
-let res = @test_throws TypeError let
-        Base.Experimental.@force_compile
-        typejoin(1, 2, 3)
-        nothing
-    end
-    err = res.value
-    @test err.func === :<:
-end
+@test typejoin(1, 2) === Any
+@test typejoin(1, 2, 3) === Any
+@test typejoin(Int, Int, 3) === Any
 
 # promote_typejoin returns a Union only with Nothing/Missing combined with concrete types
 for T in (Nothing, Missing)