From c92806b9503a6e65ee941ebe3bf41b3b1a615af4 Mon Sep 17 00:00:00 2001
From: Dustin Brody <tersec@users.noreply.github.com>
Date: Sat, 13 Jul 2019 15:58:01 +0000
Subject: [PATCH] include both static and dynamic check for invariants to
 ensure that get_crosslink_committee(...) can access all committees by ensure
 that SHARD_COUNT >= SLOTS_PER_EPOCH (#318)

* include both static and dynamic check for invariants to ensure that get_crosslink_committee(...) can access all committees by ensure that SHARD_COUNT >= SLOTS_PER_EPOCH

* add state_sim to CI, to ensure that it also doesn't break SHARD_COUNT/SLOTS_PER_EPOCH assumptions, along with just in general not breaking
---
 beacon_chain.nimble                   | 6 ++++--
 beacon_chain/spec/datatypes.nim       | 5 +++++
 beacon_chain/spec/helpers.nim         | 5 ++++-
 beacon_chain/spec/presets/minimal.nim | 2 +-
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/beacon_chain.nimble b/beacon_chain.nimble
index 4c6c36c34..6b5a7b17b 100644
--- a/beacon_chain.nimble
+++ b/beacon_chain.nimble
@@ -32,14 +32,14 @@ requires "nim >= 0.19.0",
   "libp2p"
 
 ### Helper functions
-proc buildBinary(name: string, srcDir = "./", params = "", lang = "c") =
+proc buildBinary(name: string, srcDir = "./", params = "", cmdParams = "", lang = "c") =
   if not dirExists "build":
     mkDir "build"
   # allow something like "nim test --verbosity:0 --hints:off beacon_chain.nims"
   var extra_params = params
   for i in 2..<paramCount():
     extra_params &= " " & paramStr(i)
-  exec "nim " & lang & " --out:./build/" & name & " " & extra_params & " " & srcDir & name & ".nim"
+  exec "nim " & lang & " --out:./build/" & name & " " & extra_params & " " & srcDir & name & ".nim" & " " & cmdParams
 
 ### tasks
 task test, "Run all tests":
@@ -47,3 +47,5 @@ task test, "Run all tests":
   buildBinary "all_tests", "tests/", "-r -d:release -d:chronicles_log_level=ERROR"
   # Minimal config
   buildBinary "all_tests", "tests/", "-r -d:release -d:chronicles_log_level=ERROR -d:const_preset=minimal"
+  # State sim; getting into 3rd epoch useful
+  buildBinary "state_sim", "research/", "-r -d:release", "--validators=128 --slots=140"
diff --git a/beacon_chain/spec/datatypes.nim b/beacon_chain/spec/datatypes.nim
index b5a427731..d1dcc4680 100644
--- a/beacon_chain/spec/datatypes.nim
+++ b/beacon_chain/spec/datatypes.nim
@@ -473,6 +473,11 @@ chronicles.formatIt Epoch: it.humaneEpochNum
 chronicles.formatIt BeaconBlock: it.shortLog
 chronicles.formatIt AttestationData: it.shortLog
 
+static:
+  # Ensure that get_crosslink_committee(...) can access all committees, which
+  # requires that SHARD_COUNT >= get_committee_count(...)
+  doAssert SHARD_COUNT >= SLOTS_PER_EPOCH
+
 import nimcrypto, json_serialization
 export json_serialization
 export writeValue, readValue, append, read
diff --git a/beacon_chain/spec/helpers.nim b/beacon_chain/spec/helpers.nim
index bd33d2d81..3d1107c45 100644
--- a/beacon_chain/spec/helpers.nim
+++ b/beacon_chain/spec/helpers.nim
@@ -87,7 +87,10 @@ func get_committee_count*(state: BeaconState, epoch: Epoch): uint64 =
   let committees_per_slot = clamp(
     len(active_validator_indices) div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
     1, SHARD_COUNT div SLOTS_PER_EPOCH).uint64
-  committees_per_slot * SLOTS_PER_EPOCH
+  result = committees_per_slot * SLOTS_PER_EPOCH
+
+  # Otherwise, get_crosslink_committee(...) cannot access some committees.
+  doAssert SHARD_COUNT >= result
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.8.0/specs/core/0_beacon-chain.md#get_current_epoch
 func get_current_epoch*(state: BeaconState): Epoch =
diff --git a/beacon_chain/spec/presets/minimal.nim b/beacon_chain/spec/presets/minimal.nim
index 51fd6e0f2..162560c7b 100644
--- a/beacon_chain/spec/presets/minimal.nim
+++ b/beacon_chain/spec/presets/minimal.nim
@@ -80,7 +80,7 @@ const
   MIN_ATTESTATION_INCLUSION_DELAY* = 1
 
   # Changed
-  SLOTS_PER_EPOCH* {.intdefine.} = 64
+  SLOTS_PER_EPOCH* {.intdefine.} = 8
 
   # Unchanged
   MIN_SEED_LOOKAHEAD* = 1