Improve static analysis: fix JET errors and add JET tests (#117)

This PR addresses type instabilities detected by JET.jl analysis:

**JET issues fixed:**
1. `math.jl`: Fixed `find_amsa` function returning `false` instead of a proper type
   - Changed fallback to return `nothing` instead of propagating non-AMSA values
   - Added type assertion in `copy` to inform the compiler that AMSAStyle guarantees an AMSA exists
   - Added explicit method `find_amsa(x::AMSA) = x` for direct dispatch
   - Added `find_amsa(::Nothing, rest)` to handle the nothing case properly

2. `print_human_readable.jl`: Fixed potential `nothing` indexing errors
   - `findfirst` and `findnext` can return `nothing` when pattern not found
   - Added proper nil-checks before indexing into results

**New tests added:**
- Added `test/jet_tests.jl` with JET.jl static analysis test
- Added JET as a test dependency in Project.toml

All existing tests pass with these changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Code <noreply@anthropic.com>

Author: ChrisRackauckas-Claude

Project.toml

@@ -30,6 +30,7 @@ DiffEqBase = "6.5"
 DifferentiationInterface = "0.7.7"
 FiniteDiff = "2.3"
 ForwardDiff = "0.10, 1.3"
+JET = "0.9, 0.10, 0.11"
 OrdinaryDiffEq = "6"
 OrdinaryDiffEqCore = "1.30.0, 2.0"
 OrdinaryDiffEqDifferentiation = "1.16"
@@ -42,9 +43,10 @@ StochasticDiffEq = "6.13"
 julia = "1.10"
 
 [extras]
+JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"
 OrdinaryDiffEq = "1dea7af3-3e70-54e6-95c3-0bf5283fa5ed"
 SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["OrdinaryDiffEq", "SafeTestsets", "Test"]
+test = ["JET", "OrdinaryDiffEq", "SafeTestsets", "Test"]

src/math.jl

@@ -15,7 +15,7 @@ end
 Broadcast.BroadcastStyle(::Type{<:AMSA}) = AMSAStyle()
 
 @inline function Base.copy(bc::Broadcast.Broadcasted{<:AMSAStyle})
-    first_amsa = find_amsa(bc)
+    first_amsa = find_amsa(bc)::AMSA  # Type assertion: AMSAStyle guarantees an AMSA exists
 
     out = similar(first_amsa, Base.Broadcast._broadcast_getindex_eltype(bc))
 
@@ -71,12 +71,16 @@ _nnodes(args::Tuple{}) = 0
 
 """
 `A = find_amsa(As)` returns the first AMSA among the arguments.
+
+Returns the first `AbstractMultiScaleArray` found in the arguments, or `nothing` if none found.
 """
 find_amsa(bc::Base.Broadcast.Broadcasted) = find_amsa(bc.args)
-find_amsa(args::Tuple) = !isempty(args) && find_amsa(find_amsa(args[1]), Base.tail(args))
-find_amsa(x) = x
+find_amsa(args::Tuple) = isempty(args) ? nothing : find_amsa(find_amsa(args[1]), Base.tail(args))
+find_amsa(x) = nothing
+find_amsa(x::AMSA) = x
 find_amsa(a::AMSA, rest) = a
 find_amsa(::Any, rest) = find_amsa(rest)
+find_amsa(::Nothing, rest) = find_amsa(rest)
 
 any_non_amsa(bc::Base.Broadcast.Broadcasted) = any_non_amsa(bc.args)
 any_non_amsa(args::Tuple) = any_non_amsa(any_non_amsa(args[1]), Base.tail(args))

src/print_human_readable.jl

@@ -118,8 +118,12 @@ function print_human_readable(X::AbstractMultiScaleArray; n_char_per_name = 6,
     #              ^^^^^^^^^^^
     for level in length(toprint):-1:1
         while occursin("+ ", toprint[level])
-            Move = findfirst("+ ", toprint[level])[1]
-            To = findnext(" |", toprint[level], Move[end])[1]
+            move_range = findfirst("+ ", toprint[level])
+            move_range === nothing && break
+            Move = first(move_range)
+            to_range = findnext(" |", toprint[level], last(move_range))
+            to_range === nothing && break
+            To = first(to_range)
             toprint[level] = join([
                 toprint[level][1:(Move - 1)],
                 toprint[level][(Move + 1):To],

test/jet_tests.jl

@@ -0,0 +1,9 @@
+using JET
+using MultiScaleArrays
+
+@testset "JET static analysis" begin
+    # Run JET analysis on the package
+    report = JET.report_package(MultiScaleArrays;
+        target_modules = (MultiScaleArrays,))
+    @test length(JET.get_reports(report)) == 0
+end

test/runtests.jl

@@ -1,6 +1,9 @@
 using MultiScaleArrays, OrdinaryDiffEq, DiffEqBase, StochasticDiffEq, SafeTestsets
 using Test
 
+@time @testset "JET Static Analysis" begin
+    include("jet_tests.jl")
+end
 @time @testset "Tuple Nodes" begin
     include("tuple_nodes.jl")
 end