have init --version fail when repo is already initialized with other version

init: When the repo is already initialized, and --version requests a
different version, error out rather than silently not changing the version.

CHANGELOG

@@ -15,6 +15,9 @@ git-annex (7.20190731) UNRELEASED; urgency=medium
     since it needs 64 bit git now.
   * Build with silently-1.2.5.1 on Windows; the old one used "NUL" which
     is not supported with recent versions of ghc.
+  * init: When the repo is already initialized, and --version requests a
+    different version, error out rather than silently not changing the
+    version.
 
  -- Joey Hess <id@joeyh.name>  Thu, 01 Aug 2019 00:11:56 -0400
 

Command/Init.hs

@@ -51,6 +51,12 @@ start os = starting "init" (ActionItemOther (Just $ initDesc os)) $
 
 perform :: InitOptions -> CommandPerform
 perform os = do
+	case initVersion os of
+		Nothing -> noop
+		Just wantversion -> getVersion >>= \case
+			Just v | v /= wantversion ->
+				giveup $ "This repository is already a initialized with version " ++ show (fromRepoVersion v) ++ ", not changing to requested version."
+			_ -> noop
 	initialize
 		(if null (initDesc os) then Nothing else Just (initDesc os))
 		(initVersion os)

doc/bugs/windows_test_suite_fails_to_init_direct_mode_repo.mdwn

@@ -9,3 +9,9 @@ I have not managed to reproduce this outside of the test suite.
 I wonder if perhaps the environment variable that the test suite sets
 to communicate with itself is not working on Windows, which sometimes
 has gotchas around environment variables. --[[Joey]]
+
+Hmm, I reordered the direct mode tests to come first, and the failure went
+away. Think that .t/repo gets reused, and being already a v7 repo, git annex
+init --version=7 silently did not change it. (Made that error out.)
+So the test suite should use different paths for the base repo in each test
+pass.