Discontinue datalad-core repository runner usage in datalad-annex

The new implementation uses the lean `call_git...()` utilities directly.
It also avoids the relatively heavy-handed environment patching
mechanism in the runner, in favor of the new lean `patched_env`
context manager. This is OK, because the git remote helper runs in its
own process.

Ping datalad#541

datalad_next/gitremotes/datalad_annex.py

@@ -210,8 +210,9 @@
 from datalad_next.exceptions import CapturedException
 from datalad_next.runners import (
     CommandError,
-    StdOutCapture,
     call_git,
+    call_git_oneline,
+    call_git_success,
 )
 from datalad_next.uis import ui_switcher as ui
 from datalad_next.utils import (
@@ -224,6 +225,7 @@
     get_specialremote_credential_envpatch,
     get_specialremote_credential_properties,
     needs_specialremote_credential_envpatch,
+    patched_env,
     specialremote_credential_envmap,
     update_specialremote_credential,
 )
@@ -1156,69 +1158,67 @@ def make_export_tree(repo):
     # we need to force Git to use a throwaway index file to maintain
     # the bare nature of the repoannex, git-annex would stop functioning
     # properly otherwise
-    env = os.environ.copy()
     index_file = repo.pathobj / 'datalad_tmp_index'
-    env['GIT_INDEX_FILE'] = str(index_file)
-    try:
-        for key, kinfo in RepoAnnexGitRemote.xdlra_key_locations.items():
-            # create a blob for the annex link
-            out = repo._git_runner.run(
-                ['git', 'hash-object', '-w', '--stdin'],
-                stdin=bytes(
-                    f'../../.git/annex/objects/{kinfo["prefix"]}/{key}/{key}',
-                    'utf-8'),
-                protocol=StdOutCapture)
-            linkhash = out['stdout'].strip()
-            # place link into a tree
-            out = repo._git_runner.run(
-                ['git', 'update-index', '--add', '--cacheinfo', '120000',
-                 linkhash, kinfo["loc"]],
-                protocol=StdOutCapture,
-                env=env)
-        # write the complete tree, and return ID
-        out = repo._git_runner.run(
-            ['git', 'write-tree'],
-            protocol=StdOutCapture,
-            env=env)
-        exporttree = out['stdout'].strip()
-        # this should always come out identically
-        # unless we made changes in the composition of the export tree
-        assert exporttree == '7f0e7953e93b4c9920c2bff9534773394f3a5762'
-
-        # clean slate
-        if index_file.exists():
-            index_file.unlink()
-        # fake export.log record
-        # <unixepoch>s <here>:<origin> <exporttree>
-        now_ts = datetime.datetime.now().timestamp()
-        out = repo._git_runner.run(
-            ['git', 'hash-object', '-w', '--stdin'],
-            stdin=bytes(
-                f'{now_ts}s {here}:{origin} {exporttree}\n', 'utf-8'),
-            protocol=StdOutCapture)
-        exportlog = out['stdout'].strip()
-        repo._git_runner.run(
-            ['git', 'read-tree', 'git-annex'],
-            env=env)
-        out = repo._git_runner.run(
-            ['git', 'update-index', '--add', '--cacheinfo', '100644',
-             exportlog, 'export.log'],
-            protocol=StdOutCapture,
-            env=env)
-        out = repo._git_runner.run(
-            ['git', 'write-tree'],
-            protocol=StdOutCapture,
-            env=env)
-        gaupdate = out['stdout'].strip()
-        out = repo._git_runner.run(
-            ['git', 'commit-tree', '-m', 'Fake export', '-p', 'git-annex',
-             gaupdate],
-            protocol=StdOutCapture,
-            env=env)
-        gacommit = out['stdout'].strip()
-        repo.call_git(['update-ref', 'refs/heads/git-annex', gacommit])
-    finally:
-        index_file.unlink()
+    with patched_env(GIT_INDEX_FILE=index_file):
+        try:
+            for key, kinfo in RepoAnnexGitRemote.xdlra_key_locations.items():
+                # create a blob for the annex link
+                linkhash = call_git_oneline(
+                    ['hash-object', '-w', '--stdin'],
+                    cwd=repo.pathobj,
+                    input=f'../../.git/annex/objects/{kinfo["prefix"]}/{key}/{key}',
+                ).strip()
+                # place link into a tree
+                call_git_success(
+                    ['update-index', '--add', '--cacheinfo', '120000',
+                     linkhash, kinfo["loc"]],
+                    cwd=repo.pathobj,
+                    capture_output=True,
+                )
+            # write the complete tree, and return ID
+            exporttree = call_git_oneline(
+                ['write-tree'], cwd=repo.pathobj
+            ).strip()
+            # this should always come out identically
+            # unless we made changes in the composition of the export tree
+            assert exporttree == '7f0e7953e93b4c9920c2bff9534773394f3a5762'
+
+            # clean slate
+            if index_file.exists():
+                index_file.unlink()
+            # fake export.log record
+            # <unixepoch>s <here>:<origin> <exporttree>
+            now_ts = datetime.datetime.now().timestamp()
+            exportlog = call_git_oneline(
+                ['hash-object', '-w', '--stdin'],
+                input=f'{now_ts}s {here}:{origin} {exporttree}\n',
+                cwd=repo.pathobj,
+            ).strip()
+            call_git_success(
+                ['read-tree', 'git-annex'],
+                cwd=repo.pathobj,
+            )
+            call_git_success(
+                ['update-index', '--add', '--cacheinfo', '100644',
+                 exportlog, 'export.log'],
+                cwd=repo.pathobj,
+                capture_output=True,
+            )
+            gaupdate = call_git_oneline(
+                ['write-tree'], cwd=repo.pathobj,
+            ).strip()
+            gacommit = call_git_oneline(
+                ['commit-tree', '-m', 'Fake export', '-p', 'git-annex',
+                 gaupdate],
+                cwd=repo.pathobj,
+            ).strip()
+            call_git_success(
+                ['update-ref', 'refs/heads/git-annex', gacommit],
+                cwd=repo.pathobj,
+            )
+        finally:
+            if index_file.exists():
+                index_file.unlink()
 
     return exporttree