Reapply "libfetchers: make attribute / URL query handling consistent"

The original attempt at this introduced a regression; this commit
reverts the revert and fixes the regression.

This reverts commit 3e151d4d77b5296b9da8c3ad209932d1dfa44c68.

Fix to the regression:

flakeref: fix handling of `?dir=` param for flakes in subdirs

As reported in #419[1], accessing a flake in a subdir of a Git
repository fails with the previous commit[2] applied with the error

    error: unsupported Git input attribute 'dir'

The problem is that the `dir`-param is inserted into the parsed URL if a
flake is fetched from the subdir of a Git repository. However, for the
fetching part this isn't even needed. The fix is to just pass `subdir`
as second argument to `FlakeRef` (which needs a `basedir` that can be
empty) and leave the parsedURL as-is.

Added a regression test to make sure we don't run into this again.

[1] https://git.lix.systems/lix-project/lix/issues/419
[2] e22172aaf6b6a366cecd3c025590e68fa2b91bcc,
    originally 3e151d4d77b5296b9da8c3ad209932d1dfa44c68

Change-Id: I2c72d5a32e406a7ca308e271730bd0af01c5d18b

4 files changed, 114 insertions, 1 deletions

diff --git a/tests/functional/fetchers.sh b/tests/functional/fetchers.sh
new file mode 100644
index 000000000..0f888dc33
--- /dev/null
+++ b/tests/functional/fetchers.sh
@@ -0,0 +1,91 @@
+source common.sh
+
+requireGit
+
+clearStore
+
+testFetchTreeError() {
+    rawFetchTreeArg="${1?fetchTree arg missing}"
+    messageSubstring="${2?messageSubstring missing}"
+
+    output="$(nix eval --impure --raw --expr "(builtins.fetchTree $rawFetchTreeArg).outPath" 2>&1)" && status=0 || status=$?
+    grepQuiet "$messageSubstring" <<<"$output"
+    test "$status" -ne 0
+}
+
+# github/gitlab/sourcehut fetcher input validation
+for provider in github gitlab sourcehut; do
+    # ref/rev validation
+    testFetchTreeError \
+        "{ type = \"$provider\"; owner = \"foo\"; repo = \"bar\"; ref = \",\"; }" \
+        "URL '$provider:foo/bar' contains an invalid branch/tag name"
+
+    testFetchTreeError \
+        "\"$provider://host/foo/bar/,\"" \
+        "URL '$provider:foo/bar', ',' is not a commit hash or a branch/tag name"
+
+    testFetchTreeError \
+        "\"$provider://host/foo/bar/f16d8f43dd0998cdb315a2cccf2e4d10027e7ca4?rev=abc\"" \
+        "URL '$provider://host/foo/bar/f16d8f43dd0998cdb315a2cccf2e4d10027e7ca4?rev=abc' already contains a ref or rev"
+
+    testFetchTreeError \
+        "\"$provider://host/foo/bar/ref?ref=ref2\"" \
+        "URL '$provider://host/foo/bar/ref?ref=ref2' already contains a ref or rev"
+
+    # host validation
+    testFetchTreeError \
+        "{ type = \"$provider\"; owner = \"foo\"; repo = \"bar\"; host = \"git_hub.com\"; }" \
+        "URL '$provider:foo/bar' contains an invalid instance host"
+
+    testFetchTreeError \
+        "\"$provider://host/foo/bar/ref?host=git_hub.com\"" \
+        "URL '$provider:foo/bar' contains an invalid instance host"
+
+    # invalid attributes
+    testFetchTreeError \
+        "{ type = \"$provider\"; owner = \"foo\"; repo = \"bar\"; wrong = true; }" \
+        "unsupported input attribute 'wrong'"
+
+    testFetchTreeError \
+        "\"$provider://host/foo/bar/ref?wrong=1\"" \
+        "unsupported input attribute 'wrong'"
+done
+
+# unsupported attributes w/ tarball fetcher
+testFetchTreeError \
+    "\"https://host/foo?wrong=1\"" \
+    "unsupported tarball input attribute 'wrong'. If you wanted to fetch a tarball with a query parameter, please use '{ type = \"tarball\"; url = \"...\"; }"
+
+# test for unsupported attributes / validation in git fetcher
+testFetchTreeError \
+    "\"git+https://github.com/owner/repo?invalid=1\"" \
+    "unsupported Git input attribute 'invalid'"
+
+testFetchTreeError \
+    "\"git+https://github.com/owner/repo?url=foo\"" \
+    "URL 'git+https://github.com/owner/repo?url=foo' must not override url via query param!"
+
+testFetchTreeError \
+    "\"git+https://github.com/owner/repo?ref=foo.lock\"" \
+    "invalid Git branch/tag name 'foo.lock'"
+
+testFetchTreeError \
+    "{ type = \"git\"; url =\"https://github.com/owner/repo\"; ref = \"foo.lock\"; }" \
+    "invalid Git branch/tag name 'foo.lock'"
+
+# same for mercurial
+testFetchTreeError \
+    "\"hg+https://forge.tld/owner/repo?invalid=1\"" \
+    "unsupported Mercurial input attribute 'invalid'"
+
+testFetchTreeError \
+    "{ type = \"hg\"; url = \"https://forge.tld/owner/repo\"; invalid = 1; }" \
+    "unsupported Mercurial input attribute 'invalid'"
+
+testFetchTreeError \
+    "\"hg+https://forge.tld/owner/repo?ref=,\"" \
+    "invalid Mercurial branch/tag name ','"
+
+testFetchTreeError \
+    "{ type = \"hg\"; url = \"https://forge.tld/owner/repo\"; ref = \",\"; }" \
+    "invalid Mercurial branch/tag name ','"
diff --git a/tests/functional/flakes/subdir-flake.sh b/tests/functional/flakes/subdir-flake.sh
new file mode 100644
index 000000000..399518502
--- /dev/null
+++ b/tests/functional/flakes/subdir-flake.sh
@@ -0,0 +1,20 @@
+source common.sh
+requireGit
+clearStore
+
+container="$TEST_HOME"/flake-container
+flake_dir="$container"/flake-dir
+
+createGitRepo "$container"
+mkdir -p "$flake_dir"
+writeSimpleFlake "$flake_dir"
+git -C "$container" add flake-dir
+
+pushd "$flake_dir" &>/dev/null
+    info="$(nix flake info --json)"
+    [[ "$(jq -r '.resolvedUrl' <<<"$info")" == git+file://*/flake-container?dir=flake-dir ]]
+    [[ "$(jq -r '.url' <<<"$info")" == git+file://*/flake-container?dir=flake-dir ]]
+
+    # Make sure we can actually access & build stuff in this flake.
+    nix build "path:$flake_dir#foo" -L
+popd &>/dev/null
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index cbf6a1563..7a9c7182f 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -71,6 +71,7 @@ functional_tests_scripts = [
   'flakes/build-paths.sh',
   'flakes/flake-registry.sh',
   'flakes/flake-in-submodule.sh',
+  'flakes/subdir-flake.sh',
   'gc.sh',
   'nix-collect-garbage-d.sh',
   'nix-collect-garbage-dry-run.sh',
@@ -94,6 +95,7 @@ functional_tests_scripts = [
   'fetchGitRefs.sh',
   'gc-runtime.sh',
   'tarball.sh',
+  'fetchers.sh',
   'fetchGit.sh',
   'fetchurl.sh',
   'fetchPath.sh',
diff --git a/tests/nixos/tarball-flakes.nix b/tests/nixos/tarball-flakes.nix
index ca7627bd1..5deba4a12 100644
--- a/tests/nixos/tarball-flakes.nix
+++ b/tests/nixos/tarball-flakes.nix
@@ -69,7 +69,7 @@ in
 
     # Check that we got redirected to the immutable URL.
     locked_url = info["locked"]["url"]
-    assert locked_url == "http://localhost/stable/${nixpkgs.rev}.tar.gz", f"{locked_url=} != http://localhost/stable/${nixpkgs.rev}.tar.gz"
+    assert locked_url == "http://localhost/stable/${nixpkgs.rev}.tar.gz?rev=${nixpkgs.rev}&revCount=1234", f"{locked_url=} != http://localhost/stable/${nixpkgs.rev}.tar.gz"
 
     # Check that we got the rev and revCount attributes.
     revision = info["revision"]