From a2daf4e7743cc7ab2cdc4ec5a5adc129cbad82d7 Mon Sep 17 00:00:00 2001
From: Alois Wohlschlager <alois1@gmx-topmail.de>
Date: Sun, 26 Jan 2025 11:22:03 +0100
Subject: [PATCH] libfetchers/mercurial: handle "evil refs" gracefully

If a revision is specified in a way that looks like a commit hash, Lix expects
that it actually is a commit hash. Unlike Git, Mercurial will fall back to
bookmarks, tags and branches with the specified name when a commit with the
specified hash does not exist. Previously, an assertion failure would be thrown
due to the resulting commit hash mismatch. Tell Mercurial to only take commit
hashes into account, whose non-existence is then handled gracefully.

Change-Id: I98bf020187575f3cf8176831da85872d066c4d95
---
 lix/libfetchers/mercurial.cc       | 8 ++++----
 tests/functional/fetchMercurial.sh | 5 +++++
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/lix/libfetchers/mercurial.cc b/lix/libfetchers/mercurial.cc
index f99191566..bd3037e3c 100644
--- a/lix/libfetchers/mercurial.cc
+++ b/lix/libfetchers/mercurial.cc
@@ -246,7 +246,7 @@ struct MercurialInputScheme : InputScheme
                 return makeResult(res->first, std::move(res->second));
         }
 
-        auto revOrRef = input.getRev() ? input.getRev()->gitRev() : *input.getRef();
+        auto revOrRef = input.getRev() ? fmt("id(%s)", input.getRev()->gitRev()) : *input.getRef();
 
         Attrs unlockedAttrs({
             {"type", "hg"},
@@ -269,7 +269,7 @@ struct MercurialInputScheme : InputScheme
            have to pull again. */
         if (!(input.getRev()
                 && pathExists(cacheDir)
-                && runProgram(hgOptions({ "log", "-R", cacheDir, "-r", input.getRev()->gitRev(), "--template", "1" })).second == "1"))
+                && runProgram(hgOptions({ "identify", "-R", cacheDir, "-r", revOrRef, "--template", "1" })).second == "1"))
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("fetching Mercurial repository '%s'", actualUrl));
 
@@ -294,7 +294,7 @@ struct MercurialInputScheme : InputScheme
         }
 
         auto tokens = tokenizeString<std::vector<std::string>>(
-            runHg({ "log", "-R", cacheDir, "-r", revOrRef, "--template", "{node} {count(revset('::{rev}'))} {branch}" }));
+            runHg({ "identify", "-R", cacheDir, "-r", revOrRef, "--template", "{node} {count(revset('::{rev}'))} {branch}" }));
         assert(tokens.size() == 3);
 
         input.attrs.insert_or_assign("rev", Hash::parseAny(tokens[0], HashType::SHA1).gitRev());
@@ -307,7 +307,7 @@ struct MercurialInputScheme : InputScheme
         Path tmpDir = createTempDir();
         AutoDelete delTmpDir(tmpDir, true);
 
-        runHg({ "archive", "-R", cacheDir, "-r", input.getRev()->gitRev(), tmpDir });
+        runHg({ "archive", "-R", cacheDir, "-r", fmt("id(%s)", input.getRev()->gitRev()), tmpDir });
 
         deletePath(tmpDir + "/.hg_archival.txt");
 
diff --git a/tests/functional/fetchMercurial.sh b/tests/functional/fetchMercurial.sh
index 001e3ae00..42d838766 100644
--- a/tests/functional/fetchMercurial.sh
+++ b/tests/functional/fetchMercurial.sh
@@ -26,6 +26,7 @@ rev1=$(hg log --cwd $repo -r tip --template '{node}')
 echo world > $repo/hello
 hg commit --cwd $repo -m 'Bla2'
 rev2=$(hg log --cwd $repo -r tip --template '{node}')
+hg --cwd $repo bookmark aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 
 # Fetch an unclean branch.
 echo unclean > $repo/hello
@@ -45,6 +46,10 @@ path=$(nix eval --impure --raw --expr "(builtins.fetchMercurial \"file://$repo\"
 path2=$(nix eval --impure --raw --expr "(builtins.fetchMercurial { url = \"file://$repo\"; rev = \"$rev2\"; }).outPath")
 [[ $path = $path2 ]]
 
+out=$(nix eval --impure --raw --expr "builtins.fetchMercurial { url = \"file://$repo\"; rev = \"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"; }" 2>&1) || status=$?
+[[ $status == 1 ]]
+[[ $out =~ 'hg failed with exit code' ]]
+
 # In pure eval mode, fetchMercurial with a revision should succeed.
 [[ $(nix eval --raw --expr "builtins.readFile (fetchMercurial { url = \"file://$repo\"; rev = \"$rev2\"; } + \"/hello\")") = world ]]