[REPLCompletions] improve REPLInterpreter effects of dict operations

[aviatesk]

This should allow more completions for cases involving dict operations.

[oscardssmith]

I'm not sure this use of noub is valid since we're calling user defined hash functions

[aviatesk]

Right. We can do a very much special-cased patch like

diff --git a/base/dict.jl b/base/dict.jl
index e7d4804b68..587c348989 100644
--- a/base/dict.jl
+++ b/base/dict.jl
@@ -271,7 +271,7 @@ function empty!(h::Dict{K,V}) where V where K
 end
 
 # get the index where a key is stored, or -1 if not present
-@assume_effects :terminates_locally :noub function ht_keyindex(h::Dict{K,V}, key) where V where K
+@assume_effects :terminates_locally function ht_keyindex(h::Dict{K,V}, key) where V where K
     isempty(h) && return -1
     sz = length(h.keys)
     iter = 0
@@ -294,6 +294,8 @@ end
     end
     # This line is unreachable
 end
+@assume_effects :noub ht_keyindex(h::Dict{Symbol,V}, key::Symbol) where V =
+    @invoke ht_keyindex(h::Dict{Symbol,V}, key::Any)
 
 # get (index, sh) for the key
 #     index - where a key is stored, or -pos if not present
@@ -505,10 +507,12 @@ function get!(default::Callable, h::Dict{K,V}, key::K) where V where K
     return v
 end
 
-@assume_effects :noub function getindex(h::Dict{K,V}, key) where V where K
+function getindex(h::Dict{K,V}, key) where V where K
     index = ht_keyindex(h, key)
     @inbounds return (index < 0) ? throw(KeyError(key)) : h.vals[index]::V
 end
+@assume_effects :noub getindex(h::Dict{Symbol,V}, key::Symbol) where V =
+    @invoke getindex(h::Dict{Symbol,V}, key::Any)
 
 """
     get(collection, key, default)

, which obviously only improves effects for Dict{Symbol, Any}.
Or, alternatively, we can implement call-site @assume_effects and do something like:

diff --git a/base/dict.jl b/base/dict.jl
index e7d4804b68..3dfde3d395 100644
--- a/base/dict.jl
+++ b/base/dict.jl
@@ -162,7 +162,7 @@ _shorthash7(hsh::UInt) = (hsh >> (8sizeof(UInt)-7))%UInt8 | 0x80
 # hashindex (key, sz) - computes optimal position and shorthash7
 #     idx - optimal position in the hash table
 #     sh::UInt8 - short hash (7 highest hash bits)
-function hashindex(key, sz)
+function hashindex(key, sz::Int)
     hsh = hash(key)::UInt
     idx = (((hsh % Int) & (sz-1)) + 1)::Int
     return idx, _shorthash7(hsh)
@@ -172,7 +172,7 @@ end
 @propagate_inbounds isslotfilled(h::Dict, i::Int) = (h.slots[i] & 0x80) != 0
 @propagate_inbounds isslotmissing(h::Dict, i::Int) = h.slots[i] == 0x7f
 
-@constprop :none function rehash!(h::Dict{K,V}, newsz = length(h.keys)) where V where K
+@constprop :none function rehash!(h::Dict{K,V}, newsz::Int = length(h.keys)) where V where K
     olds = h.slots
     oldk = h.keys
     oldv = h.vals
@@ -271,7 +271,7 @@ function empty!(h::Dict{K,V}) where V where K
 end
 
 # get the index where a key is stored, or -1 if not present
-@assume_effects :terminates_locally :noub function ht_keyindex(h::Dict{K,V}, key) where V where K
+@assume_effects :terminates_locally function ht_keyindex(h::Dict{K,V}, key) where V where K
     isempty(h) && return -1
     sz = length(h.keys)
     iter = 0
@@ -282,8 +282,8 @@ end
 
     @inbounds while true
         isslotempty(h,index) && return -1
-        if h.slots[index] == sh
-            k = keys[index]
+        if sh == @assume_effects :noub h.slots[index]
+            k = @assume_effects :noub keys[index]
             if (key ===  k || isequal(key, k))
                 return index
             end
@@ -505,9 +505,9 @@ function get!(default::Callable, h::Dict{K,V}, key::K) where V where K
     return v
 end
 
-@assume_effects :noub function getindex(h::Dict{K,V}, key) where V where K
+function getindex(h::Dict{K,V}, key) where V where K
     index = ht_keyindex(h, key)
-    @inbounds return (index < 0) ? throw(KeyError(key)) : h.vals[index]::V
+    return (index < 0) ? throw(KeyError(key)) : @assume_effects :noub @inbounds h.vals[index]::V
 end
 
 """

while letting the compiler automatically prove :noub of the other parts of code including custom hash implementation.

[aviatesk]

Now this is based on #52400.