Fix updating pins on crates which track Alire-generated files

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
@@ -199,7 +201,7 @@ package body Alire.User_Pins is
          Trace.Detail ("Checking out pin " & Utils.TTY.Name (Crate) & " at "
                        & TTY.URL (Destination));
 
-         --  If the fetch URL has been changed, fall back to checkout
+         --  If the fetch URL has been changed, do a fresh 'git clone'.
          --
          --  Note that VCSs.Git.Clone converts the URL to a git-friendly form
          --  with VCSs.Repo, so this is what the output of 'git config' should
@@ -223,11 +225,44 @@ package body Alire.User_Pins is
          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

src/alire/alire-vcss-git.adb

@@ -292,6 +292,21 @@ package body Alire.VCSs.Git is
          return Alire.Errors.Get (E);
    end Commit_All;
 
+   -------------------------
+   -- Discard_Uncommitted --
+   -------------------------
+
+   function Discard_Uncommitted (Repo : Directory_Path) return Outcome
+   is
+      Guard : Directories.Guard (Directories.Enter (Repo)) with Unreferenced;
+   begin
+      Run_Git (Empty_Vector & "reset" & "-q" & "--hard" & "HEAD");
+      return Outcome_Success;
+   exception
+      when E : others =>
+         return Alire.Errors.Get (E);
+   end Discard_Uncommitted;
+
    ----------
    -- Push --
    ----------

src/alire/alire-vcss-git.ads

@@ -104,6 +104,9 @@ package Alire.VCSs.Git is
    --  Add and commit all changes in a given repo; commiter will be set to the
    --  user email stored in our config.
 
+   function Discard_Uncommitted (Repo : Directory_Path) return Outcome;
+   --  Reset all uncommitted changes to tracked files
+
    function Push (Repo   : Directory_Path;
                   Remote : String;
                   Force  : Boolean := False;
@@ -184,6 +187,9 @@ package Alire.VCSs.Git is
                     return Outcome;
    --  Update and track Branch, if given.
    --
+   --  Does not discard uncommitted changes, so will fail if there are local
+   --  changes which conflict with the update.
+   --
    --  Raises Checked_Error when the repo has multiple remotes configured and
    --  Branch is not the same as the current HEAD.
 

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

@@ -0,0 +1,82 @@
+"""
+Check updating a branch pin when 'config/*' files are tracked.
+"""
+
+
+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, assert_not_substring
+from drivers.helpers import git_branch, git_commit_file, init_git_repo
+
+
+# Create crate yyy, with git tracking the 'config/*' files
+init_local_crate("yyy")
+yyy_path = os.getcwd()
+with open(".gitignore") as f:
+    gitignore_content = f.read()
+gitignore_content = gitignore_content.replace("/config/\n", "")
+with open(".gitignore", "w") as f:
+    f.write(gitignore_content)
+init_git_repo(".")
+default_branch = git_branch()
+os.chdir("..")
+
+# Create and build another crate, with yyy's default branch added as a pin
+init_local_crate()
+xxx_path = os.getcwd()
+alr_pin("yyy", url=f"git+file:{yyy_path}", branch=default_branch)
+run_alr("build")
+
+# Verify that the cached copy of yyy has a dirty repo (due to changes to the
+# 'config/*' files)
+cached_yyy_path = os.path.join(xxx_path, "alire", "cache", "pins", "yyy")
+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())
+
+# Add commits to yyy's default branch, including a change to a file in 'config/'
+os.chdir(yyy_path)
+git_commit_file(
+    "Change_config", "config/yyy_config.gpr", "This is a new addition\n", "a"
+)
+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 (subject to user
+# confirmation)
+os.chdir(xxx_path)
+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')

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

@@ -0,0 +1,3 @@
+driver: python-script
+indexes:
+    compiler_only_index: {}