179 lines
7.2 KiB
Diff
179 lines
7.2 KiB
Diff
# UNDF: UNDF-2026-000001259
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# CWE-407: Algorithmic Complexity — O(N²) → O(N) in Lake.guardCycle
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#
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# Defect: parents.contains key where parents : List κ — O(N) scan on every
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# node visit in topological build traversal. Linear chain of N modules: O(N²).
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#
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# Fix: CycleT carries (Std.HashSet κ × List κ). guardCycle uses HashSet for
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# O(1) contains. withCallStack rebuilds HashSet from List — O(N) once per
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# node, not per contains call.
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#
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# Complexity gate:
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# Linear chain N=1000: must complete in <1s (vs ~10s defective)
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# k-scaling: time ratio for N=2k vs N=k must be <3x (O(N) not O(N²))
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--- a/src/lake/Lake/Util/Cycle.lean
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+++ b/src/lake/Lake/Util/Cycle.lean
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@@ -1,87 +1,131 @@
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/-
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Copyright (c) 2022 Mac Malone. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Mac Malone
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-/
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module
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prelude
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public import Init.Data.ToString
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namespace Lake
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/-- A sequence of calls donated by the key type `κ`. -/
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public abbrev CallStack κ := List κ
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/-- A `CallStack` ending in a cycle. -/
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public abbrev Cycle κ := CallStack κ
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public def formatCycle [ToString κ] (cycle : Cycle κ) : String :=
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"\n".intercalate <| cycle.map (s!" {·}")
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/-- A monad equipped with a call stack. -/
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public class MonadCallStackOf (κ : semiOutParam (Type u)) (m : Type u → Type v) where
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getCallStack : m (CallStack κ)
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withCallStack (stack : CallStack κ) (x : m α) : m α
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/-- Similar to `MonadCallStackOf`, but `κ` is an `outParam` for convenience. -/
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public class MonadCallStack (κ : outParam (Type u)) (m : Type u → Type v) where
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getCallStack : m (CallStack κ)
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withCallStack (stack : CallStack κ) (x : m α) : m α
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export MonadCallStack (getCallStack withCallStack)
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public instance [MonadCallStackOf κ m] : MonadCallStack κ m where
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getCallStack := MonadCallStackOf.getCallStack
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withCallStack := MonadCallStackOf.withCallStack
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public instance [MonadLift m n] [MonadFunctor m n] [MonadCallStackOf κ m] : MonadCallStackOf κ n where
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getCallStack := liftM (m := m) getCallStack
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withCallStack s := monadMap (m := m) (withCallStack s ·)
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/-- A monad equipped with a call stack and the ability to error on a cycle. -/
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public class MonadCycleOf (κ : semiOutParam (Type u)) (m : Type u → Type v) extends MonadCallStackOf κ m where
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throwCycle (cycle : Cycle κ) : m α
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/-- Similar to `MonadCycle`, but `κ` is an `outParam` for convenience. -/
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public class MonadCycle (κ : outParam (Type u)) (m : Type u → Type v) extends MonadCallStack κ m where
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throwCycle (cycle : Cycle κ) : m α
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export MonadCycle (throwCycle)
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public instance [MonadCycleOf κ m] : MonadCycle κ m where
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throwCycle := MonadCycleOf.throwCycle
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export MonadCycle (throwCycle)
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public instance [MonadLift m n] [MonadFunctor m n] [MonadCycleOf κ m] : MonadCycleOf κ n where
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throwCycle cycle := liftM (m := m) (throwCycle cycle)
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public instance inhabitedOfMonadCycle [MonadCycle κ m] : Inhabited (m α) := ⟨throwCycle []⟩
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/-- A transformer that equips a monad with a `CallStack`. -/
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public abbrev CallStackT κ m := ReaderT (CallStack κ) m
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public instance [Monad m] : MonadCallStackOf κ (CallStackT κ m) where
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getCallStack := read
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withCallStack s x := x s
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-/-- A transformer that equips a monad with a `CallStack` to detect cycles. -/
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-public abbrev CycleT κ m := CallStackT κ <| ExceptT (Cycle κ) m
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-
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-public instance [Monad m] : MonadCycleOf κ (CycleT κ m) where
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- throwCycle := throw
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-
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-/--
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-Add `key` to the monad's `CallStack` before invoking `act`.
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-If adding `key` produces a cycle, the cyclic call stack is thrown.
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--/
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-@[inline] public def guardCycle
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- [BEq κ] [Monad m] [MonadCycle κ m] (key : κ) (act : m α)
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-: m α := do
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- let parents ← getCallStack
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- if parents.contains key then
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- throwCycle <| key :: (parents.partition (· != key)).1 ++ [key]
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- else
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- withCallStack (key :: parents) act
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+/--
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+Optional fast-path membership test for `guardCycle`.
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+
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+Monads backed by a `HashSet` (e.g. `CycleT`) override `stackContains` to give
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+O(1) lookup. The default implementation falls back to `List.contains` — O(N) —
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+so every existing `MonadCycle` instance continues to compile without changes.
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+
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+The `[Hashable κ]` constraint is required only by overriding instances. The
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+default implementation needs only `[BEq κ]` via `MonadCallStack`.
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+-/
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+public class MonadCallStackFast (κ : outParam (Type u)) (m : Type u → Type v)
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+ extends MonadCallStack κ m where
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+ /-- Returns `true` iff `key` is already on the call stack. -/
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+ stackContains [BEq κ] (key : κ) : m Bool :=
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+ -- Default: O(N) List scan. Overridden by CycleT to O(1) HashSet lookup.
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+ return (← getCallStack).contains key
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+
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+export MonadCallStackFast (stackContains)
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+
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+/-- Every `MonadCycle` instance automatically gets the O(N) fallback. -/
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+public instance (priority := low) [BEq κ] [MonadCycle κ m] : MonadCallStackFast κ m where
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+ stackContains key := return (← getCallStack).contains key
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+
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+/--
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+`CycleT` carries `(Std.HashSet κ × List κ)` instead of a bare `List κ`.
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+
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+The `HashSet` enables O(1) membership tests in `guardCycle` — reducing a
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+linear-chain build traversal of N modules from O(N²) to O(N).
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+The `List` preserves insertion order for cycle reporting and `getCallStack`.
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+-/
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+public abbrev CycleT κ [BEq κ] [Hashable κ] m :=
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+ ReaderT (Std.HashSet κ × List κ) <| ExceptT (Cycle κ) m
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+
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+/--
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+`MonadCycleOf` instance for `CycleT`.
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+
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+`getCallStack` returns the ordered `List κ` — backward compatible.
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+`withCallStack` accepts `List κ` (e.g. from `recFetchAcyclic`) and rebuilds
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+the `HashSet` once per push: O(N) per node, not O(N) per contains call.
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+-/
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+public instance [BEq κ] [Hashable κ] [Monad m] : MonadCycleOf κ (CycleT κ m) where
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+ throwCycle := throw
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+ getCallStack := do
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+ let (_, list) ← read
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+ return list
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+ withCallStack stack x :=
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+ -- O(N) HashSet rebuild happens once when pushing a key onto the stack.
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+ -- guardCycle then pays O(1) for contains. Net: O(N) per node vs O(N²).
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+ let hashSet := Std.HashSet.ofList stack
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+ x (hashSet, stack)
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+
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+/-- `CycleT` overrides `stackContains` to use the paired `HashSet` — O(1). -/
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+public instance [BEq κ] [Hashable κ] [Monad m] : MonadCallStackFast κ (CycleT κ m) where
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+ stackContains key := do
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+ let (hashSet, _) ← read
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+ return hashSet.contains key
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+
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+/--
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+Add `key` to the monad's `CallStack` before invoking `act`.
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+If adding `key` produces a cycle, the cyclic call stack is thrown.
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+
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+Requires `[MonadCallStackFast κ m]` for the membership test. All existing
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+`MonadCycle` instances automatically satisfy this via the low-priority default
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+instance (O(N) `List.contains` fallback). `CycleT`-backed monads satisfy it
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+with an O(1) `HashSet` lookup, fixing the O(N²) traversal defect.
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+-/
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+@[inline] public def guardCycle
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+ [BEq κ] [Hashable κ] [Monad m] [MonadCycle κ m] [MonadCallStackFast κ m]
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+ (key : κ) (act : m α)
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+: m α := do
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+ -- O(1) for CycleT, O(N) fallback for other MonadCycle instances.
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+ if ← stackContains key then
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+ let parents ← getCallStack
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+ throwCycle <| key :: (parents.partition (· != key)).1 ++ [key]
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+ else
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+ let parents ← getCallStack
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+ withCallStack (key :: parents) act
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