implement new array assignment shape matching rule. fixes #4048, fixes #4383

this rule ignores singleton dimensions, and allows the last dimension of
one side to match all trailing dimensions of the other.

Author: JeffBezanson

base/array.jl

@@ -593,20 +593,7 @@ function setindex!(A::Array, x, I::Union(Real,AbstractArray)...)
             assign_cache = Dict()
         end
         X = x
-        nel = 1
-        for idx in I
-            nel *= length(idx)
-        end
-        if length(X) != nel
-            throw(DimensionMismatch(""))
-        end
-        if ndims(X) > 1
-            for i = 1:length(I)
-                if size(X,i) != length(I[i])
-                    throw(DimensionMismatch(""))
-                end
-            end
-        end
+        setindex_shape_check(X, I...)
         gen_array_index_map(assign_cache, storeind -> quote
                               A[$storeind] = X[refind]
                               refind += 1

base/operators.jl

@@ -206,21 +206,83 @@ index_shape(I::Real...) = ()
 index_shape(i, I...) = tuple(length(i), index_shape(I...)...)
 
 # check for valid sizes in A[I...] = X where X <: AbstractArray
+# we want to allow dimensions that are equal up to permutation, but only
+# for permutations that leave array elements in the same linear order.
+# those are the permutations that preserve the order of the non-singleton
+# dimensions.
 function setindex_shape_check(X::AbstractArray, I...)
+    li = length(I)
+    ii = 1
     nel = 1
-    for idx in I
-        nel *= length(idx)
-    end
-    if length(X) != nel
-        error("dimensions must match")
-    end
-    if ndims(X) > 1
-        for i = 1:length(I)
-            if size(X,i) != length(I[i])
-                error("dimensions must match")
+    xi = 1
+    ndx = ndims(X)
+    match = true
+    while ii < li
+        lii = length(I[ii])::Int
+        ii += 1
+        if lii != 1
+            nel *= lii
+            local lxi
+            while true
+                lxi = size(X,xi)
+                xi += 1
+                if lxi != 1 || xi > ndx
+                    break
+                end
+            end
+            if xi > ndx
+                trailing = lii
+                while ii <= li
+                    lii = length(I[ii])::Int
+                    trailing *= lii
+                    ii += 1
+                end
+                # X's last dimension can match all the trailing indexes
+                if lxi == trailing && match
+                    return
+                else
+                    throw(DimensionMismatch(""))
+                end
+            else
+                if lxi != lii
+                    match = false
+                end
             end
         end
     end
+
+    # last index can match X's trailing dimensions
+    lii = length(I[ii])::Int
+    nel *= lii
+    if lii != trailingsize(X,xi)
+        match = false
+    end
+
+    if !(match && length(X)==nel)
+        throw(DimensionMismatch(""))
+    end
+end
+
+setindex_shape_check(X::AbstractArray) = (length(X)==1 || throw(DimensionMismatch("")))
+
+setindex_shape_check(X::AbstractArray, i) =
+    (length(X)==length(i) || throw(DimensionMismatch("")))
+
+setindex_shape_check{T}(X::AbstractArray{T,1}, i) =
+    (length(X)==length(i) || throw(DimensionMismatch("")))
+
+setindex_shape_check{T}(X::AbstractArray{T,1}, i, j) =
+    (length(X)==length(i)*length(j) || throw(DimensionMismatch("")))
+
+function setindex_shape_check{T}(X::AbstractArray{T,2}, i, j)
+    li, lj = length(i), length(j)
+    if length(X) != li*lj
+        throw(DimensionMismatch(""))
+    end
+    sx1 = size(X,1)
+    if !(li == 1 || li == sx1 || sx1 == 1)
+        throw(DimensionMismatch(""))
+    end
 end
 
 # convert to integer index