From 582cabd743f670ba176c7a214ce9b6da05dee2e2 Mon Sep 17 00:00:00 2001
From: Mate Soos <mate.soos@ethereum.org>
Date: Mon, 7 Oct 2024 14:36:41 +0200
Subject: [PATCH] Trying to fix issues regarding --code-a/--code-b inputs

Better documentation, better error printing

Related to #581
---
 doc/src/equivalence-checking-tutorial.md | 16 ++++++++++++++++
 src/EVM/Format.hs                        |  2 +-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/doc/src/equivalence-checking-tutorial.md b/doc/src/equivalence-checking-tutorial.md
index b0a93dc81..46e124ffc 100644
--- a/doc/src/equivalence-checking-tutorial.md
+++ b/doc/src/equivalence-checking-tutorial.md
@@ -102,3 +102,19 @@ consume the same amount of gas and have widely different EVM bytecodes. Yet for
 an outside observer, they behave the same. Notice that hevm didn't simply fuzz
 the contract and within a given out of time it didn't find a counterexample.
 Instead, it _proved_ the two equivalent from an outside observer perspective.
+
+## Dealing with Already Compiled Contracts
+
+If the contracts have already been compiled into a hex string, you can paste
+them into files `a.txt` and `b.txt` and compare them via:
+
+```shell
+$ hevm equivalence --code-a "$(<a.txt)" --code-b "$(<b.txt)"
+```
+
+You can also copy-paste the contents of the hex strings directly into the
+command line, although this can become cumbersome:
+
+```shell
+$ hevm equivalence --code-a "6080604052348015600e575f80fd5b50600436106026575f3560e01c8063881fc77c14602a575b5f80fd5b60306032565b005b5f600190506002811460455760446048565b5b50565b7f4e487b71000000000000000000000000000000000000000000000000000000005f52600160045260245ffdfea26469706673582212208c57ae04774d9ebae7d1d11f9d5e730075068bc7988d4c83c6fed85b7f062e7b64736f6c634300081a0033" --code-b "6080604052348015600e575f80fd5b50600436106030575f3560e01c806385c2fc7114603457806386ae330914603c575b5f80fd5b603a6044565b005b60426055565b005b60025f541460535760526066565b5b565b60035f541460645760636066565b5b565b7f4e487b71000000000000000000000000000000000000000000000000000000005f52600160045260245ffdfea2646970667358221220bd2f8a1ba281308f845e212d2b5eceab85e029909fa2409cdca7ede039bae26564736f6c634300081a0033"
+```
diff --git a/src/EVM/Format.hs b/src/EVM/Format.hs
index cd518e175..b044c11d5 100644
--- a/src/EVM/Format.hs
+++ b/src/EVM/Format.hs
@@ -828,7 +828,7 @@ hexByteString :: String -> ByteString -> ByteString
 hexByteString msg bs =
   case BS16.decodeBase16Untyped bs of
     Right x -> x
-    _ -> internalError $ "invalid hex bytestring for " ++ msg
+    _ -> internalError $ "invalid hex bytestring for '" ++ msg ++ "'. Bytestring provided: '" ++ show bs ++ "'"
 
 hexText :: Text -> ByteString
 hexText t =