From 53af75af57ffd5b15b1fc8bbf1880fcc82a245a3 Mon Sep 17 00:00:00 2001
From: Chris Penner <christopher.penner@gmail.com>
Date: Mon, 13 Dec 2021 12:14:16 -0600
Subject: [PATCH] Check for empty deletes in move.namespace

---
 .../src/Unison/Codebase/Editor/HandleInput.hs | 28 +++++-----
 .../transcripts/empty-namespaces.output.md    | 54 +++++++++++++++++++
 2 files changed, 70 insertions(+), 12 deletions(-)

diff --git a/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs b/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs
index 7e9279cd0..b32a14cd0 100644
--- a/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs
+++ b/unison-cli/src/Unison/Codebase/Editor/HandleInput.hs
@@ -340,8 +340,6 @@ loop = do
             unless (Set.null misses) $
               respond $ SearchTermsNotFound (Set.toList misses)
             traverse_ go (if isTerm then tmRefs else tpRefs)
-          branchExists dest _x = respond $ BranchAlreadyExists dest
-          branchExistsSplit = branchExists . Path.unsplit'
           typeExists dest = respond . TypeAlreadyExists dest
           termExists dest = respond . TermAlreadyExists dest
           inputDescription :: LoopState.InputDescription
@@ -671,16 +669,22 @@ loop = do
                   BranchUtil.makeSetBranch (resolveSplit' dest) b
                 ]
               success
-            MoveBranchI (Just src) dest ->
-              maybe (branchNotFound' src) srcOk (getAtSplit' src)
-              where
-                srcOk b = maybe (destOk b) (branchExistsSplit dest) (getAtSplit' dest)
-                destOk b = do
-                  stepManyAt
-                    [ BranchUtil.makeDeleteBranch (resolveSplit' src),
-                      BranchUtil.makeSetBranch (resolveSplit' dest) b
-                    ]
-                  success -- could give rando stats about new defns
+            MoveBranchI (Just src) dest -> unlessError $ do
+              srcBranch <- case getAtSplit' src of
+                Just existingSrc | not (Branch.isEmpty0 (Branch.head existingSrc)) -> do
+                  pure existingSrc
+                _ -> throwError $ BranchNotFound (Path.unsplit' src)
+              case getAtSplit' dest of
+                Just existingDest
+                  | not (Branch.isEmpty0 (Branch.head existingDest)) -> do
+                    -- Branch exists and isn't empty, print an error
+                    throwError (BranchAlreadyExists (Path.unsplit' dest))
+                _ -> pure ()
+              lift $ stepManyAt
+                [ BranchUtil.makeDeleteBranch (resolveSplit' src),
+                  BranchUtil.makeSetBranch (resolveSplit' dest) srcBranch
+                ]
+              lift $ success -- could give rando stats about new defns
             MovePatchI src dest -> do
               psrc <- getPatchAtSplit' src
               pdest <- getPatchAtSplit' dest
diff --git a/unison-src/transcripts/empty-namespaces.output.md b/unison-src/transcripts/empty-namespaces.output.md
index 68accf1a2..e844a848e 100644
--- a/unison-src/transcripts/empty-namespaces.output.md
+++ b/unison-src/transcripts/empty-namespaces.output.md
@@ -82,6 +82,8 @@ deleted.x = 1
 stuff.thing = 2
 ```
 
+## fork
+
 I should be allowed to fork over a deleted namespace
 
 ```ucm
@@ -112,3 +114,55 @@ The history from the `deleted` namespace should have been overwritten by the his
   □ #3bm1524lb7 (start of history)
 
 ```
+## move.namespace
+
+```unison
+moveoverme.x = 1
+moveme.y = 2
+```
+
+I should be able to move a namespace over-top of a deleted namespace.
+The history should be that of the moved namespace.
+
+```ucm
+.> delete.namespace moveoverme
+
+  Removed definitions:
+  
+    1. x : ##Nat
+  
+  Tip: You can use `undo` or `reflog` to undo this change.
+
+.> history moveme
+
+  Note: The most recent namespace hash is immediately below this
+        message.
+  
+  
+  
+  □ #ldl7o5e9i5 (start of history)
+
+.> move.namespace moveme moveoverme
+
+  Done.
+
+.> history moveoverme
+
+  Note: The most recent namespace hash is immediately below this
+        message.
+  
+  ⊙ #3ahcthnkvt
+  
+    + Adds / updates:
+    
+      y
+  
+  ⊙ #qjc20aua9h
+  
+    - Deletes:
+    
+      x
+  
+  □ #hkrqt3tm05 (start of history)
+
+```