engineering/java-topology
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions
java-topology/tools/tickets/defects/ghc-0004.md
russell@unturf.com db29a08762 undefect. CWE-407 — 92 sites, 42 ecosystems 
B&W print-friendly diagrams + tinkerpop-0001 + wave-3 proof sections.
Squash of 94 local commits onto remote master.
2026-03-26 19:48:18 -04:00

1.2 KiB
Raw Blame History

id repo severity status created patched patch
ghc-0004 ghc MEDIUM PATCHED 2026-03-23 2026-03-23 defects/ghc/patch/ghc-cwe407-set-membership.patch

Defect

File: compiler/GHC/Tc/TyCl/Utils.hs:973 Pattern: elem in constructor list during type-class checking Complexity: O(n) per check Language: Haskell

Description

During type-class checking, GHC tests whether a data constructor is in a list using elem, which performs a linear scan. This check is applied per-constructor during the verification of derived instances and type-class obligations. For data types with many constructors, or when checks are repeated across multiple class instances, the O(n) per-check cost accumulates into noticeable compilation slowdown.

Fix

Replace: con `elem` conList With: con `S.member` conSet Data structure change: conList: [DataCon] → conSet: Set DataCon

Work required

  • Patch in defects/ghc/patch/
  • Unit test — asserts exact operation counts before/after (in defects/ghc/unit/)
  • Integration test (in defects/ghc/integration/)
  • Benchmark — before/after on V=100,200,400,800 (in defects/ghc/bench/)
  • White paper section