Drop the requirement for dist-git-merge in discover/fmf

tests/discover/distgit.sh

@@ -378,7 +378,7 @@ EOF
         WORKDIR=/var/tmp/tmt/XXX
         rlRun -s 'tmt run --keep --scratch --id $WORKDIR plans --default \
             discover --how fmf --dist-git-source --dist-git-type fedora --url $CLONED_RPMS_TMT \
-            --dist-git-merge tests --name tests/prepare/install$ prepare provision -h local'
+            tests --name tests/prepare/install$ prepare provision -h local'
         assert_tests $WORKDIR tests/prepare/install
     rlPhaseEnd
 
@@ -387,9 +387,9 @@ EOF
             rlRun 'pushd tmt'
             WORKDIR=/var/tmp/tmt/XXX
             rlRun -s "tmt run --keep --scratch --id $WORKDIR plans --default discover -v --how fmf \
-            --dist-git-source --dist-git-merge --ref e2d36db --dist-git-extract ${prefix}tmt-1.7.0/tests/execute/framework/data \
-            tests --name ^/tests/beakerlib/with-framework\$ prepare provision -h local"
-            assert_tests $WORKDIR /tests/beakerlib/with-framework
+            --dist-git-source --ref 518edd9 --dist-git-extract ${prefix}tmt-1.74.0/tests/execute/basic/data \
+            tests --name ^/test/shell/good\$ prepare provision -h local"
+            assert_tests $WORKDIR /test/shell/good
 
             rlRun 'popd'
         rlPhaseEnd
@@ -398,10 +398,10 @@ EOF
     rlPhaseStartTest "Specify URL and REF of DistGit repo (Fedora)"
         WORKDIR=/var/tmp/tmt/XXX
         rlRun -s 'tmt run --keep --scratch --id $WORKDIR plans --default discover -v --how fmf \
-        --dist-git-source --ref e2d36db --dist-git-merge  --dist-git-init \
+        --dist-git-source --ref 518edd9 \
         --url https://src.fedoraproject.org/rpms/tmt.git \
-        tests --name tests/prepare/install$  prepare provision -h local'
-        assert_tests $WORKDIR "/tmt-1.7.0/tests/prepare/install"
+        tests --name ^/tests/prepare/install$  prepare provision -h local'
+        assert_tests $WORKDIR "/tests/prepare/install"
     rlPhaseEnd
 
     rlPhaseStartTest "fmf and git root don't match"

tmt/steps/discover/fmf.py

@@ -650,17 +650,10 @@ def go(self, *, path: Optional[Path] = None, logger: Optional[tmt.log.Logger] =
         super().go(path=path, logger=logger)
 
         dist_git_source = self.get('dist-git-source', False)
-        dist_git_merge = self.get('dist-git-merge', False)
 
         # No tests are selected in some cases
         self._tests: list[tmt.Test] = []
 
-        # Self checks
-        if dist_git_source and not dist_git_merge and (self.data.ref or self.data.url):
-            raise tmt.utils.DiscoverError(
-                "Cannot manipulate with dist-git without the `--dist-git-merge` option."
-            )
-
         self.log_import_plan_details()
 
         # Dist-git source processing during discover step
@@ -678,9 +671,7 @@ def go(self, *, path: Optional[Path] = None, logger: Optional[tmt.log.Logger] =
                     raise tmt.utils.DiscoverError(
                         f"Directory '{fmf_root}' is not a git repository."
                     )
-
-                distgit_dir = self.test_dir if self.data.ref else git_root
-                self.process_distgit_source(distgit_dir)
+                self.process_distgit_source(git_root)
                 return
             except Exception as error:
                 raise tmt.utils.DiscoverError("Failed to process 'dist-git-source'.") from error
@@ -700,7 +691,6 @@ def process_distgit_source(self, distgit_dir: Path) -> None:
         )
 
         # Copy rest of files so TMT_SOURCE_DIR has patches, sources and spec file
-        # FIXME 'worktree' could be used as source_dir when 'url' is not set
         tmt.utils.filesystem.copy_tree(
             distgit_dir,
             self.source_dir,