Require user confirmation before discarding changes

src/alire/alire-user_pins.adb

@@ -9,6 +9,8 @@ with Alire.VFS;
 
 with AAA.Strings;
 
+with CLIC.User_Input;
+
 with GNAT.OS_Lib;
 
 package body Alire.User_Pins is
@@ -216,24 +218,51 @@ package body Alire.User_Pins is
             return;
          end if;
 
-         --  Discard any uncommitted changes (e.g. files in 'config/' which
-         --  Alire has automatically generated).
-         --  These can cause Update's 'git pull' command to fail.
-
-         VCSs.Git.Discard_Uncommitted (Repo => Destination).Assert;
-
          --  Finally update. In case the branch has just been changed by the
          --  user in the manifest, the following call will also take care of
          --  it.
 
          Put_Info ("Pulling " & Utils.TTY.Name (Crate)
                    & " branch " & TTY.URL (Branch) & "...");
 
-         if not VCSs.Git.Handler.Update (Destination, Branch).Success then
-            Raise_Checked_Error
-              ("Update of repository at " & TTY.URL (Destination)
-               & " failed, re-run with -vv -d for details");
-         end if;
+         declare
+            use CLIC.User_Input;
+            Result : Outcome := VCSs.Git.Handler.Update (Destination, Branch);
+         begin
+            if not Result.Success
+              and then VCSs.Git.Handler.Status (Destination) in VCSs.Git.Dirty
+              and then Query
+                (Question =>
+                   "Do you want to discard local uncommitted changes in '"
+                   & Destination
+                   & "'?"
+                   & New_Line
+                   & "These changes were probably generated by Alire, so "
+                   & "select 'Yes' unless you made them yourself.",
+                 Valid    => (Yes | No => True, others => False),
+                 Default  => Yes)
+                = Yes
+            then
+               --  One reason why the update may fail is if there are
+               --  uncommitted changes in the local clone which would conflict
+               --  with the update, so we discard such changes and try again.
+               --
+               --  This generally happens if the crate's repo tracks
+               --  Alire-generated files (e.g. those in 'config/'). However, it
+               --  is conceivable the user might have made changes to the
+               --  checkout in the 'alire/cache/pins' directory themselves, so
+               --  we require user confirmation before discarding anything.
+
+               VCSs.Git.Discard_Uncommitted (Repo => Destination).Assert;
+               Result := VCSs.Git.Handler.Update (Destination, Branch);
+            end if;
+
+            if not Result.Success then
+               Raise_Checked_Error
+                 ("Update of repository at " & TTY.URL (Destination)
+                  & " failed, re-run with -vv -d for details");
+            end if;
+         end;
       end Update;
 
    begin

testsuite/tests/pin/branch-update-dirty/test.py

@@ -4,10 +4,11 @@
 
 
 import os
+import re
 import subprocess
 
 from drivers.alr import run_alr, alr_pin, init_local_crate
-from drivers.asserts import assert_match, assert_in_file
+from drivers.asserts import assert_match, assert_in_file, assert_not_substring
 from drivers.helpers import git_branch, git_commit_file, init_git_repo
 
 
@@ -44,12 +45,38 @@
 )
 git_commit_file("Add_test_file", "test_file", "This is a new file\n")
 
-# Check that the dirty repo doesn't prevent updating the pin
+# Check that the dirty repo doesn't prevent updating the pin (subject to user
+# confirmation)
 os.chdir(xxx_path)
-run_alr("update")
+p = run_alr("update")
+assert_match(
+    (
+        ".*Do you want to discard local uncommitted changes in '"
+        rf"{re.escape(cached_yyy_path)}'\?"
+        ".*These changes were probably generated by Alire, so select 'Yes' "
+        r"unless you made them yourself\."
+    ),
+    p.out
+)
 
 # Check that the update was successful
 assert_in_file(os.path.join(cached_yyy_path, "test_file"), "This is a new file")
 
+# Reset the cached clone by only one commit and repeat the above. This time the
+# update should work without user confirmation, as there will be no conflict
+# (only 'test_file' needs to be updated).
+os.chdir(cached_yyy_path)
+p = subprocess.run(["git", "reset", "--hard", "HEAD~"]).check_returncode()
+os.chdir(xxx_path)
+run_alr("build")
+os.chdir(cached_yyy_path)
+p = subprocess.run(["git", "status"], capture_output=True)
+p.check_returncode()
+assert_match(r".*modified:\s*config/yyy_config\.gpr", p.stdout.decode())
+os.chdir(xxx_path)
+p = run_alr("update")
+assert_not_substring("Do you want to discard local uncommitted changes", p.out)
+assert_in_file(os.path.join(cached_yyy_path, "test_file"), "This is a new file")
+
 
 print('SUCCESS')