Added recursive merge function for NamedTuple, addresses #29215 (#29259)

base/namedtuple.jl

@@ -213,16 +213,25 @@ end
 end
 
 """
-    merge(a::NamedTuple, b::NamedTuple)
+    merge(a::NamedTuple, bs::NamedTuple...)
 
-Construct a new named tuple by merging two existing ones.
-The order of fields in `a` is preserved, but values are taken from matching
-fields in `b`. Fields present only in `b` are appended at the end.
+Construct a new named tuple by merging two or more existing ones, in a left-associative
+manner. Merging proceeds left-to-right, between pairs of named tuples, and so the order of fields
+present in both the leftmost and rightmost named tuples take the same position as they are found in the
+leftmost named tuple. However, values are taken from matching fields in the rightmost named tuple that
+contains that field. Fields present in only the rightmost named tuple of a pair are appended at the end.
+A fallback is implemented for when only a single named tuple is supplied,
+with signature `merge(a::NamedTuple)`.
 
 ```jldoctest
 julia> merge((a=1, b=2, c=3), (b=4, d=5))
 (a = 1, b = 4, c = 3, d = 5)
 ```
+
+```jldoctest
+julia> merge((a=1, b=2), (b=3, c=(d=1,)), (c=(d=2,),))
+(a = 1, b = 3, c = (d = 2,))
+```
 """
 function merge(a::NamedTuple{an}, b::NamedTuple{bn}) where {an, bn}
     if @generated
@@ -241,6 +250,10 @@ merge(a::NamedTuple{()}, b::NamedTuple) = b
 
 merge(a::NamedTuple, b::Iterators.Pairs{<:Any,<:Any,<:Any,<:NamedTuple}) = merge(a, b.data)
 
+merge(a::NamedTuple, b::NamedTuple, cs::NamedTuple...) = merge(merge(a, b), cs...)
+
+merge(a::NamedTuple) = a
+
 """
     merge(a::NamedTuple, iterable)
 

test/namedtuple.jl

@@ -243,3 +243,8 @@ y = map(v -> (a=v.a, b=v.a + v.b), [(a=1, b=missing), (a=1, b=2)])
 # Iterator constructor
 @test NamedTuple{(:a, :b), Tuple{Int, Float64}}(Any[1.0, 2]) === (a=1, b=2.0)
 @test NamedTuple{(:a, :b)}(Any[1.0, 2]) === (a=1.0, b=2)
+
+# Left-associative merge, issue #29215
+@test merge((a=1, b=2), (b=3, c=4), (c=5,)) === (a=1, b=3, c=5)
+@test merge((a=1, b=2), (b=3, c=(d=1,)), (c=(d=2,),)) === (a=1, b=3, c=(d=2,))
+@test merge((a=1, b=2)) === (a=1, b=2)