From 2c2fd4946f96e6839ecbfb4cf61318d8910e7e8f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kasper=20Ga=C5=82kowski?= <kpg@posteo.net>
Date: Wed, 6 Apr 2022 19:28:12 +0200
Subject: [PATCH] don't assume that rev is a SHA1 hash

This was a problem when writing a fetcher that uses e.g. sha256 hashes
for revisions. This doesn't actually do anything new, but allows for
creating such fetchers in the future (perhaps when support for Git's
SHA256 object format gains more popularity).
---
 src/libfetchers/fetchers.cc | 15 ++++++++++++---
 src/libutil/hash.cc         |  2 +-
 src/libutil/hash.hh         |  2 --
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 976f40d3b..6957d2da4 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -238,9 +238,18 @@ std::optional<std::string> Input::getRef() const
 
 std::optional<Hash> Input::getRev() const
 {
-    if (auto s = maybeGetStrAttr(attrs, "rev"))
-        return Hash::parseAny(*s, htSHA1);
-    return {};
+    std::optional<Hash> hash = {};
+
+    if (auto s = maybeGetStrAttr(attrs, "rev")) {
+        try {
+            hash = Hash::parseAnyPrefixed(*s);
+        } catch (BadHash &e) {
+            // Default to sha1 for backwards compatibility with existing flakes
+            hash = Hash::parseAny(*s, htSHA1);
+        }
+    }
+
+    return hash;
 }
 
 std::optional<uint64_t> Input::getRevCount() const
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index a4d632161..d2fd0c15a 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -155,7 +155,7 @@ static std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_
 {
     bool isSRI = false;
 
-    // Parse the has type before the separater, if there was one.
+    // Parse the hash type before the separator, if there was one.
     std::optional<HashType> optParsedType;
     {
         auto hashRaw = splitPrefixTo(rest, ':');
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 56b5938b3..00f70a572 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -93,13 +93,11 @@ public:
 
     std::string gitRev() const
     {
-        assert(type == htSHA1);
         return to_string(Base16, false);
     }
 
     std::string gitShortRev() const
     {
-        assert(type == htSHA1);
         return std::string(to_string(Base16, false), 0, 7);
     }