Add aliasing warnings to docstrings for mutating functions in Base (#…

…50824)

base/Base.jl

@@ -115,6 +115,12 @@ time_ns() = ccall(:jl_hrtime, UInt64, ())
 
 start_base_include = time_ns()
 
+# A warning to be interpolated in the docstring of every dangerous mutating function in Base, see PR #50824
+const _DOCS_ALIASING_WARNING = """
+!!! warning
+    Behavior can be unexpected when any mutated argument shares memory with any other argument.
+"""
+
 ## Load essential files and libraries
 include("essentials.jl")
 include("ctypes.jl")

base/abstractarray.jl

@@ -905,6 +905,8 @@ If `dst` and `src` are of the same type, `dst == src` should hold after
 the call. If `dst` and `src` are multidimensional arrays, they must have
 equal [`axes`](@ref).
 
+$(_DOCS_ALIASING_WARNING)
+
 See also [`copyto!`](@ref).
 
 !!! compat "Julia 1.1"
@@ -1391,6 +1393,8 @@ _unsafe_ind2sub(sz, i) = (@inline; _ind2sub(sz, i))
 Store values from array `X` within some subset of `A` as specified by `inds`.
 The syntax `A[inds...] = X` is equivalent to `(setindex!(A, X, inds...); X)`.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = zeros(2,2);
@@ -3365,6 +3369,8 @@ end
 Like [`map`](@ref), but stores the result in `destination` rather than a new
 collection. `destination` must be at least as large as the smallest collection.
 
+$(_DOCS_ALIASING_WARNING)
+
 See also: [`map`](@ref), [`foreach`](@ref), [`zip`](@ref), [`copyto!`](@ref).
 
 # Examples

base/abstractset.jl

@@ -65,6 +65,8 @@ const ∪ = union
 Construct the [`union`](@ref) of passed in sets and overwrite `s` with the result.
 Maintain order with arrays.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> a = Set([3, 4, 5]);
@@ -182,6 +184,8 @@ const ∩ = intersect
 
 Intersect all passed in sets and overwrite `s` with the result.
 Maintain order with arrays.
+
+$(_DOCS_ALIASING_WARNING)
 """
 function intersect!(s::AbstractSet, itrs...)
     for x in itrs
@@ -218,6 +222,8 @@ setdiff(s) = union(s)
 Remove from set `s` (in-place) each element of each iterable from `itrs`.
 Maintain order with arrays.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> a = Set([1, 3, 4, 5]);
@@ -272,6 +278,8 @@ symdiff(s) = symdiff!(copy(s))
 Construct the symmetric difference of the passed in sets, and overwrite `s` with the result.
 When `s` is an array, the order is maintained.
 Note that in this case the multiplicity of elements matters.
+
+$(_DOCS_ALIASING_WARNING)
 """
 function symdiff!(s::AbstractSet, itrs...)
     for x in itrs

base/accumulate.jl

@@ -42,6 +42,8 @@ end
     cumsum!(B, A; dims::Integer)
 
 Cumulative sum of `A` along the dimension `dims`, storing the result in `B`. See also [`cumsum`](@ref).
+
+$(_DOCS_ALIASING_WARNING)
 """
 cumsum!(B::AbstractArray{T}, A; dims::Integer) where {T} =
     accumulate!(add_sum, B, A, dims=dims)
@@ -150,6 +152,8 @@ cumsum(itr) = accumulate(add_sum, itr)
 
 Cumulative product of `A` along the dimension `dims`, storing the result in `B`.
 See also [`cumprod`](@ref).
+
+$(_DOCS_ALIASING_WARNING)
 """
 cumprod!(B::AbstractArray{T}, A; dims::Integer) where {T} =
     accumulate!(mul_prod, B, A, dims=dims)
@@ -159,6 +163,8 @@ cumprod!(B::AbstractArray{T}, A; dims::Integer) where {T} =
 
 Cumulative product of a vector `x`, storing the result in `y`.
 See also [`cumprod`](@ref).
+
+$(_DOCS_ALIASING_WARNING)
 """
 cumprod!(y::AbstractVector, x::AbstractVector) = cumprod!(y, x, dims=1)
 
@@ -301,6 +307,8 @@ Cumulative operation `op` on `A` along the dimension `dims`, storing the result
 Providing `dims` is optional for vectors.  If the keyword argument `init` is given, its
 value is used to instantiate the accumulation.
 
+$(_DOCS_ALIASING_WARNING)
+
 See also [`accumulate`](@ref), [`cumsum!`](@ref), [`cumprod!`](@ref).
 
 # Examples

base/array.jl

@@ -322,6 +322,8 @@ source and `do` in the destination (1-indexed).
 The `unsafe` prefix on this function indicates that no validation is performed to ensure
 that N is inbounds on either array. Incorrect usage may corrupt or segfault your program, in
 the same manner as C.
+
+$(_DOCS_ALIASING_WARNING)
 """
 function unsafe_copyto!(dest::Array{T}, doffs, src::Array{T}, soffs, n) where T
     t1 = @_gc_preserve_begin dest
@@ -1784,6 +1786,8 @@ place of the removed items; in this case, `indices` must be a `AbstractUnitRange
 To insert `replacement` before an index `n` without removing any items, use
 `splice!(collection, n:n-1, replacement)`.
 
+$(_DOCS_ALIASING_WARNING)
+
 !!! compat "Julia 1.5"
     Prior to Julia 1.5, `indices` must always be a `UnitRange`.
 
@@ -2762,6 +2766,8 @@ Remove the items at all the indices which are not given by `inds`,
 and return the modified `a`.
 Items which are kept are shifted to fill the resulting gaps.
 
+$(_DOCS_ALIASING_WARNING)
+
 `inds` must be an iterator of sorted and unique integer indices.
 See also [`deleteat!`](@ref).
 

base/asyncmap.jl

@@ -394,6 +394,8 @@ length(itr::AsyncGenerator) = length(itr.collector.enumerator)
 
 Like [`asyncmap`](@ref), but stores output in `results` rather than
 returning a collection.
+
+$(_DOCS_ALIASING_WARNING)
 """
 function asyncmap!(f, r, c1, c...; ntasks=0, batch_size=nothing)
     foreach(identity, AsyncCollector(f, r, c1, c...; ntasks=ntasks, batch_size=batch_size))

base/combinatorics.jl

@@ -147,6 +147,8 @@ it is even faster to write into a pre-allocated output array with `u .= @view v[
 (Even though `permute!` overwrites `v` in-place, it internally requires some allocation
 to keep track of which elements have been moved.)
 
+$(_DOCS_ALIASING_WARNING)
+
 See also [`invpermute!`](@ref).
 
 # Examples
@@ -176,6 +178,8 @@ Note that if you have a pre-allocated output array (e.g. `u = similar(v)`),
 it is quicker to instead employ `u[p] = v`.  (`invpermute!` internally
 allocates a copy of the data.)
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = [1, 1, 3, 4];

base/multidimensional.jl

@@ -1169,8 +1169,7 @@ circshift!(dest::AbstractArray, src, ::Tuple{}) = copyto!(dest, src)
 Circularly shift, i.e. rotate, the data in `src`, storing the result in
 `dest`. `shifts` specifies the amount to shift in each dimension.
 
-The `dest` array must be distinct from the `src` array (they cannot
-alias each other).
+$(_DOCS_ALIASING_WARNING)
 
 See also [`circshift`](@ref).
 """
@@ -1228,6 +1227,8 @@ their indices; any offset results in a (circular) wraparound. If the
 arrays have overlapping indices, then on the domain of the overlap
 `dest` agrees with `src`.
 
+$(_DOCS_ALIASING_WARNING)
+
 See also: [`circshift`](@ref).
 
 # Examples

base/reducedim.jl

@@ -448,6 +448,8 @@ _count(f, A::AbstractArrayOrBroadcasted, dims, init) = mapreduce(_bool(f), add_s
 Count the number of elements in `A` for which `f` returns `true` over the
 singleton dimensions of `r`, writing the result into `r` in-place.
 
+$(_DOCS_ALIASING_WARNING)
+
 !!! compat "Julia 1.5"
     inplace `count!` was added in Julia 1.5.
 
@@ -525,8 +527,8 @@ sum(f, A::AbstractArray; dims)
     sum!(r, A)
 
 Sum elements of `A` over the singleton dimensions of `r`, and write results to `r`.
-Note that since the sum! function is intended to operate without making any allocations,
-the target should not alias with the source.
+
+$(_DOCS_ALIASING_WARNING)
 
 # Examples
 ```jldoctest
@@ -601,6 +603,8 @@ prod(f, A::AbstractArray; dims)
 
 Multiply elements of `A` over the singleton dimensions of `r`, and write results to `r`.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = [1 2; 3 4]
@@ -678,6 +682,8 @@ maximum(f, A::AbstractArray; dims)
 
 Compute the maximum value of `A` over the singleton dimensions of `r`, and write results to `r`.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = [1 2; 3 4]
@@ -755,6 +761,8 @@ minimum(f, A::AbstractArray; dims)
 
 Compute the minimum value of `A` over the singleton dimensions of `r`, and write results to `r`.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = [1 2; 3 4]
@@ -820,6 +828,8 @@ extrema(f, A::AbstractArray; dims)
 
 Compute the minimum and maximum value of `A` over the singleton dimensions of `r`, and write results to `r`.
 
+$(_DOCS_ALIASING_WARNING)
+
 !!! compat "Julia 1.8"
     This method requires Julia 1.8 or later.
 
@@ -895,6 +905,8 @@ all(::Function, ::AbstractArray; dims)
 
 Test whether all values in `A` along the singleton dimensions of `r` are `true`, and write results to `r`.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = [true false; true false]
@@ -968,6 +980,8 @@ any(::Function, ::AbstractArray; dims)
 Test whether any values in `A` along the singleton dimensions of `r` are `true`, and write
 results to `r`.
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> A = [true false; true false]
@@ -1085,6 +1099,8 @@ end
 Find the minimum of `A` and the corresponding linear index along singleton
 dimensions of `rval` and `rind`, and store the results in `rval` and `rind`.
 `NaN` is treated as less than all other values except `missing`.
+
+$(_DOCS_ALIASING_WARNING)
 """
 function findmin!(rval::AbstractArray, rind::AbstractArray, A::AbstractArray;
                   init::Bool=true)
@@ -1156,6 +1172,8 @@ end
 Find the maximum of `A` and the corresponding linear index along singleton
 dimensions of `rval` and `rind`, and store the results in `rval` and `rind`.
 `NaN` is treated as greater than all other values except `missing`.
+
+$(_DOCS_ALIASING_WARNING)
 """
 function findmax!(rval::AbstractArray, rind::AbstractArray, A::AbstractArray;
                   init::Bool=true)

base/sort.jl

@@ -1587,6 +1587,8 @@ v[ix[k]] == partialsort(v, k)
 The return value is the `k`th element of `ix` if `k` is an integer, or view into `ix` if `k` is
 a range.
 
+$(Base._DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> v = [3, 1, 2, 1];
@@ -1711,6 +1713,8 @@ end
 Like [`sortperm`](@ref), but accepts a preallocated index vector or array `ix` with the same `axes` as `A`.
 `ix` is initialized to contain the values `LinearIndices(A)`.
 
+$(Base._DOCS_ALIASING_WARNING)
+
 !!! compat "Julia 1.9"
     The method accepting `dims` requires at least Julia 1.9.
 

doc/src/manual/functions.md

@@ -102,6 +102,9 @@ As a common convention in Julia (not a syntactic requirement), such a function w
 [typically be named `f!(x, y)`](@ref man-punctuation) rather than `f(x, y)`, as a visual reminder at
 the call site that at least one of the arguments (often the first one) is being mutated.
 
+!!! warning "Shared memory between arguments"
+    The behavior of a mutating function can be unexpected when a mutated argument shares memory with another argument, a situation known as aliasing (e.g. when one is a view of the other).
+    Unless the function docstring explicitly indicates that aliasing produces the expected result, it is the responsibility of the caller to ensure proper behavior on such inputs.
 
 ## Argument-type declarations