Add a preference system for turning on/off slow fallbacks

This gives a good way to balance development vs usage. For development, you want to just error if you hit any slower path. But for users, code should just work. Thus the slower fallbacks were given a preference system for allowing error throwing, without forcing all users to have to always see errors on new types just for more optimizations.

src/ArrayInterface.jl

@@ -1,5 +1,7 @@
 module ArrayInterface
 
+const SLOWFALLBACKS = @load_preference("slow_fallbacks", true)
+
 using LinearAlgebra
 using SparseArrays
 using SuiteSparse
@@ -282,7 +284,7 @@ function ismutable end
     ismutable(::Type{T}) -> Bool
 
 Query whether instances of type `T` are mutable or not, see
-https://github.com/JuliaDiffEq/RecursiveArrayTools.jl/issues/19.
+https://github.com/SciML/RecursiveArrayTools.jl/issues/19.
 """
 ismutable(x) = ismutable(typeof(x))
 function ismutable(::Type{T}) where {T <: AbstractArray}
@@ -460,12 +462,15 @@ Returns the number.
 """
 bunchkaufman_instance(a::Number) = a
 
-"""
-bunchkaufman_instance(a::Any) -> cholesky(a, check=false)
+@static if SLOWFALLBACKS
+    """
+    bunchkaufman_instance(a::Any) -> cholesky(a, check=false)
 
-Returns the number.
-"""
-bunchkaufman_instance(a::Any) = bunchkaufman(a, check = false)
+    Slow fallback which gets the instance via factorization. Should get
+    specialized for new matrix types.
+    """
+    bunchkaufman_instance(a::Any) = bunchkaufman(a, check = false)
+end
 
 """
 cholesky_instance(A, pivot = LinearAlgebra.RowMaximum()) -> cholesky_factorization_instance
@@ -487,13 +492,15 @@ Returns the number.
 """
 cholesky_instance(a::Number, pivot = LinearAlgebra.RowMaximum()) = a
 
-"""
-cholesky_instance(a::Any, pivot = LinearAlgebra.RowMaximum()) -> cholesky(a, check=false)
+@static if SLOWFALLBACKS
+    """
+    cholesky_instance(a::Any, pivot = LinearAlgebra.RowMaximum()) -> cholesky(a, check=false)
 
-Slow fallback which gets the instance via factorization. Should get
-specialized for new matrix types.
-"""
-cholesky_instance(a::Any, pivot = LinearAlgebra.RowMaximum()) = cholesky(a, pivot, check = false)
+    Slow fallback which gets the instance via factorization. Should get
+    specialized for new matrix types.
+    """
+    cholesky_instance(a::Any, pivot = LinearAlgebra.RowMaximum()) = cholesky(a, pivot, check = false)
+end
 
 """
 ldlt_instance(A) -> ldlt_factorization_instance
@@ -515,13 +522,15 @@ Returns the number.
 """
 ldlt_instance(a::Number) = a
 
-"""
-ldlt_instance(a::Any) -> ldlt(a, check=false)
+@static if SLOWFALLBACKS
+    """
+    ldlt_instance(a::Any) -> ldlt(a, check=false)
 
-Slow fallback which gets the instance via factorization. Should get
-specialized for new matrix types.
-"""
-ldlt_instance(a::Any) = ldlt(a)
+    Slow fallback which gets the instance via factorization. Should get
+    specialized for new matrix types.
+    """
+    ldlt_instance(a::Any) = ldlt(a)
+end
 
 """
   lu_instance(A) -> lu_factorization_instance
@@ -558,13 +567,15 @@ Returns the number.
 """
 lu_instance(a::Number) = a
 
-"""
-    lu_instance(a::Any) -> lu(a, check=false)
+@static if SLOWFALLBACKS
+    """
+        lu_instance(a::Any) -> lu(a, check=false)
 
-Slow fallback which gets the instance via factorization. Should get
-specialized for new matrix types.
-"""
-lu_instance(a::Any) = lu(a, check = false)
+    Slow fallback which gets the instance via factorization. Should get
+    specialized for new matrix types.
+    """
+    lu_instance(a::Any) = lu(a, check = false)
+end
 
 """
   qr_instance(A) -> qr_factorization_instance
@@ -588,13 +599,15 @@ Returns the number.
 """
 qr_instance(a::Number) = a
 
-"""
-    qr_instance(a::Any) -> qr(a)
+@static if SLOWFALLBACKS
+    """
+        qr_instance(a::Any) -> qr(a)
 
-Slow fallback which gets the instance via factorization. Should get
-specialized for new matrix types.
-"""
-qr_instance(a::Any) = qr(a)# check = false)
+    Slow fallback which gets the instance via factorization. Should get
+    specialized for new matrix types.
+    """
+    qr_instance(a::Any) = qr(a)# check = false)
+end
 
 """
   svd_instance(A) -> qr_factorization_instance
@@ -613,13 +626,15 @@ Returns the number.
 """
 svd_instance(a::Number) = a
 
-"""
-    svd_instance(a::Any) -> svd(a)
+@static if SLOWFALLBACKS
+    """
+        svd_instance(a::Any) -> svd(a)
 
-Slow fallback which gets the instance via factorization. Should get
-specialized for new matrix types.
-"""
-svd_instance(a::Any) = svd(a) #check = false)
+    Slow fallback which gets the instance via factorization. Should get
+    specialized for new matrix types.
+    """
+    svd_instance(a::Any) = svd(a) #check = false)
+end
 
 """
     safevec(v)
@@ -1034,3 +1049,4 @@ import Requires
 end
 
 end # module
+