Short circuit linesearch for now

src/linesearch.jl

@@ -8,7 +8,7 @@ differentiation for fast Vector Jacobian Products.
 
 ### Arguments
 
-  - `method`: the line search algorithm to use. Defaults to `Static()`, which means that the
+  - `method`: the line search algorithm to use. Defaults to `nothing`, which means that the
     step size is fixed to the value of `alpha`.
   - `autodiff`: the automatic differentiation backend to use for the line search. Defaults to
     `AutoFiniteDiff()`, which means that finite differencing is used to compute the VJP.
@@ -22,19 +22,31 @@ differentiation for fast Vector Jacobian Products.
     α
 end
 
-function LineSearch(; method = Static(), autodiff = AutoFiniteDiff(), alpha = true)
+function LineSearch(; method = nothing, autodiff = AutoFiniteDiff(), alpha = true)
     return LineSearch(method, autodiff, alpha)
 end
 
 @inline function init_linesearch_cache(ls::LineSearch, args...)
     return init_linesearch_cache(ls.method, ls, args...)
 end
 
+@concrete struct NoLineSearchCache
+    α
+end
+
+function init_linesearch_cache(::Nothing, ls, f::F, u, p, fu, iip) where {F}
+    return NoLineSearchCache(convert(eltype(u), ls.α))
+end
+
+perform_linesearch!(cache::NoLineSearchCache, u, du) = cache.α
+
 # LineSearches.jl doesn't have a supertype so default to that
-function init_linesearch_cache(_, ls, f::F, u, p, fu, iip) where {F <: Function}
+function init_linesearch_cache(_, ls, f::F, u, p, fu, iip) where {F}
     return LineSearchesJLCache(ls, f, u, p, fu, iip)
 end
 
+# FIXME: The closures lead to too many unnecessary runtime dispatches which leads to the
+#        massive increase in precompilation times.
 # Wrapper over LineSearches.jl algorithms
 @concrete mutable struct LineSearchesJLCache
     f
@@ -45,8 +57,7 @@ end
     ls
 end
 
-function LineSearchesJLCache(ls::LineSearch, f::F, u::Number, p, _,
-    ::Val{false}) where {F <: Function}
+function LineSearchesJLCache(ls::LineSearch, f::F, u::Number, p, _, ::Val{false}) where {F}
     eval_f(u, du, α) = eval_f(u - α * du)
     eval_f(u) = f(u, p)
 
@@ -87,8 +98,7 @@ function LineSearchesJLCache(ls::LineSearch, f::F, u::Number, p, _,
     return LineSearchesJLCache(eval_f, ϕ, dϕ, ϕdϕ, convert(eltype(u), ls.α), ls)
 end
 
-function LineSearchesJLCache(ls::LineSearch, f::F, u, p, fu1,
-    IIP::Val{iip}) where {iip, F <: Function}
+function LineSearchesJLCache(ls::LineSearch, f::F, u, p, fu1, IIP::Val{iip}) where {iip, F}
     fu = iip ? deepcopy(fu1) : nothing
     u_ = _mutable_zero(u)
 
@@ -202,7 +212,7 @@ end
 end
 
 function init_linesearch_cache(alg::LiFukushimaLineSearch, ls::LineSearch, f::F, _u, p, _fu,
-    ::Val{iip}) where {iip, F <: Function}
+    ::Val{iip}) where {iip, F}
     fu = iip ? deepcopy(_fu) : nothing
     u = iip ? deepcopy(_u) : nothing
     return LiFukushimaLineSearchCache{iip}(f, p, u, fu, alg, ls.α)

src/utils.jl

@@ -216,7 +216,7 @@ function __get_concrete_algorithm(alg, prob)
         use_sparse_ad ? AutoSparseFiniteDiff() : AutoFiniteDiff()
     else
         tag = NonlinearSolveTag()
-        use_sparse_ad ? AutoSparseForwardDiff(; tag) : AutoForwardDiff(; tag)
+        (use_sparse_ad ? AutoSparseForwardDiff : AutoForwardDiff)(; tag)
     end
     return set_ad(alg, ad)
 end