add a dirty flag to Dict

makes `get!` work with default functions that modify the dict. fixes #9573

base/dict.jl

@@ -325,10 +325,11 @@ type Dict{K,V} <: Associative{K,V}
  ndel::Int
  count::Int
  deleter::Function
+ dirty::Bool
 
  function Dict()
  n = 16
- new(zeros(UInt8,n), Array(K,n), Array(V,n), 0, 0, identity)
+ new(zeros(UInt8,n), Array(K,n), Array(V,n), 0, 0, identity, false)
  end
  function Dict(kv)
  h = Dict{K,V}()
@@ -424,6 +425,7 @@ function rehash!{K,V}(h::Dict{K,V}, newsz = length(h.keys))
  oldv = h.vals
  sz = length(olds)
  newsz = _tablesz(newsz)
+ h.dirty = true
  if h.count == 0
  resize!(h.slots, newsz)
  fill!(h.slots, 0)
@@ -490,6 +492,7 @@ function empty!{K,V}(h::Dict{K,V})
  resize!(h.vals, sz)
  h.ndel = 0
  h.count = 0
+ h.dirty = true
  return h
 end
 
@@ -561,6 +564,7 @@ function _setindex!(h::Dict, v, key, index)
  h.keys[index] = key
  h.vals[index] = v
  h.count += 1
+ h.dirty = true
 
  sz = length(h.keys)
  # Rehash now if necessary
@@ -614,8 +618,17 @@ function get!{K,V}(default::Callable, h::Dict{K,V}, key0)
 
  index > 0 && return h.vals[index]
 
+ h.dirty = false
  v = convert(V, default())
- _setindex!(h, v, key, -index)
+ if h.dirty
+ index = ht_keyindex2(h, key)
+ end
+ if index > 0
+ h.keys[index] = key
+ h.vals[index] = v
+ else
+ _setindex!(h, v, key, -index)
+ end
  return v
 end
 
@@ -684,6 +697,7 @@ function _delete!(h::Dict, index)
  ccall(:jl_arrayunset, Void, (Any, UInt), h.vals, index-1)
  h.ndel += 1
  h.count -= 1
+ h.dirty = true
  h
 end