avoid Pair constructor being excessively specialized by Core.Compiler (#46684)

Author: vtjnash

base/Base.jl

@@ -107,9 +107,6 @@ include("options.jl")
 include("promotion.jl")
 include("tuple.jl")
 include("expr.jl")
-Pair{A, B}(@nospecialize(a), @nospecialize(b)) where {A, B} = (@inline; Pair{A, B}(convert(A, a)::A, convert(B, b)::B))
-#Pair{Any, B}(@nospecialize(a::Any), b) where {B} = (@inline; Pair{Any, B}(a, Base.convert(B, b)::B))
-#Pair{A, Any}(a, @nospecialize(b::Any)) where {A} = (@inline; Pair{A, Any}(Base.convert(A, a)::A, b))
 include("pair.jl")
 include("traits.jl")
 include("range.jl")
@@ -125,6 +122,13 @@ include("pointer.jl")
 include("refvalue.jl")
 include("refpointer.jl")
 
+# now replace the Pair constructor (relevant for NamedTuples) with one that calls our Base.convert
+delete_method(which(Pair{Any,Any}, (Any, Any)))
+@eval function (P::Type{Pair{A, B}})(@nospecialize(a), @nospecialize(b)) where {A, B}
+    @inline
+    return $(Expr(:new, :P, :(convert(A, a)), :(convert(B, b))))
+end
+
 # The REPL stdlib hooks into Base using this Ref
 const REPL_MODULE_REF = Ref{Module}()
 
@@ -429,6 +433,7 @@ end
 for m in methods(include)
     delete_method(m)
 end
+
 # These functions are duplicated in client.jl/include(::String) for
 # nicer stacktraces. Modifications here have to be backported there
 include(mod::Module, _path::AbstractString) = _include(identity, mod, _path)

base/boot.jl

@@ -838,8 +838,10 @@ struct Pair{A, B}
     # but also mark the whole function with `@inline` to ensure we will inline it whenever possible
     # (even if `convert(::Type{A}, a::A)` for some reason was expensive)
     Pair(a, b) = new{typeof(a), typeof(b)}(a, b)
-    Pair{A, B}(a::A, b::B) where {A, B} = new(a, b)
-    Pair{Any, Any}(@nospecialize(a::Any), @nospecialize(b::Any)) = new(a, b)
+    function Pair{A, B}(@nospecialize(a), @nospecialize(b)) where {A, B}
+        @inline
+        return new(a::A, b::B)
+    end
 end
 
 ccall(:jl_set_istopmod, Cvoid, (Any, Bool), Core, true)