russell@unturf.com
1dee074618
findAndVerifyWindowGrace() recurses over parent GraphNodes without a visited accumulator. Kafka Streams GraphNode is a genuine DAG (addChild wires parent→child with multiple parents allowed), so a diamond topology causes 2^D recursive calls. Fix: thread an IdentityHashMap<GraphNode,Long> memo through recursion; memoize on first visit, return cached result on revisit. 8/8 unit tests PASS; D=10 defect count=3071 vs patched O(N). Diamond-recursion CLEAN markers added for: flink, neo4j, janusgraph, tinkerpop, dgraph, zookeeper, storm, ant, gradle, graal, eclipse-jdt, exposed, intellij, kotlin, scala3, hibernate-0007 (prior session work now committed).
44 lines
1.7 KiB
Markdown
44 lines
1.7 KiB
Markdown
# Scala 3 Compiler — Diamond Recursion CWE-407 Scan: CLEAN
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**Pattern:** Recursive cycle/reachability without visited set (O(2^D) on diamond DAGs)
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**Scan date:** 2026-03-29
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**Scope:** `compiler/src/dotty/`
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## Method
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Searched for `isCyclic`, `hasCycle`, `createsCycle`, `isReachable`, `canReach`,
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`hasPath`, `detectCycle` across all Scala sources. Examined recursive functions
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for missing visited-accumulator parameters.
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## Key candidates reviewed
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### `SymDenotations.computeBaseType()` — `recur()` inner function
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`compiler/src/dotty/tools/dotc/core/SymDenotations.scala` around line 2265.
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`recur(tp)` is called recursively but uses `btrCache` as a memoization cache.
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Before recursing, it checks `btrCache.lookup(tp)` for a sentinel value (`NoPrefix`)
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that indicates a cycle in progress. This is a memo-table anti-cycle pattern. CLEAN.
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### `OrderingConstraint.dependsOn()`
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`compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala` line 286.
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Uses `deps.at(param).exists(qualifies)` — direct set lookup, not recursive. CLEAN.
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### `Checking.CheckNonCyclicMap`
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`compiler/src/dotty/tools/dotc/typer/Checking.scala` line 257.
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`CheckNonCyclicMap` extends `TypeMap` and uses a `cycleOK` flag plus
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`CyclicReference` exception for cycle detection. Not diamond recursion — uses
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exception-based unwinding, not unbounded recursion. CLEAN.
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### `SymUtils.isReachable`
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`compiler/src/dotty/tools/dotc/core/SymUtils.scala` line 211.
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Returns `ctx.owner.isContainedIn(sym)` — single O(depth) tree traversal.
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Not a DAG traversal. CLEAN.
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## Verdict
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CLEAN for diamond recursion pattern. Scala 3 compiler uses `btrCache` memo tables,
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exception-based cycle detection, and O(depth) tree traversals. No unprotected
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recursive DAG traversal found.
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