manifest_xml: Improve error message on base check fail

Previous error had a scent of alien blob to it
due to dumping the list in a single long line, so
improve print for human readability.

Example of new fail:

error: in `manifest`: detected base-revision mismatch, updates needed:
remove-project name build/make:
  base fccb6b3e884b4b964e795f5f8865f6bbb4722b5a vs revision 6e9a0c16f20d1cfcf08b8b9cb42301b6c9712862
remove-project path build/soong:
  base 16b3c9ca0679bb376966866afb849322c8aec79f vs revision b7490575c16b87d861a532b03bd1b2d076b6fa0b
extend-project name platform/system/sepolicy:
  base c2652856e9f0e0433d78cfb481efe392d6f5dbc4 vs revision cf9a73f92f503ffc4bd3e726164babfb40a9fcaf

Test: repo manifest > /dev/null && echo 'Nice =)'
      on various good and bad test manifests
Change-Id: I8d741e11c69ef9e4f8cf09e32aa0868b6daa5acd
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/619921
Tested-by: Fredrik de Groot <fredrik.de.groot@haleytek.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Fredrik de Groot <fredrik.de.groot@haleytek.com>

manifest_xml.py

diff --git a/manifest_xml.py b/manifest_xml.py
index 379ce09..0e80435 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -1519,9 +1519,9 @@
                         if base_revision:
                             if p.revisionExpr != base_revision:
                                 failed_revision_changes.append(
-                                    "extend-project name %s mismatch base "
-                                    "%s vs revision %s"
-                                    % (name, base_revision, p.revisionExpr)
+                                    f"extend-project name {name}:\n  "
+                                    f"base {base_revision} vs "
+                                    f"revision {p.revisionExpr}"
                                 )
                         p.SetRevision(revision)
 
@@ -1622,9 +1622,9 @@
                             if base_revision:
                                 if p.revisionExpr != base_revision:
                                     failed_revision_changes.append(
-                                        "remove-project name %s mismatch base "
-                                        "%s vs revision %s"
-                                        % (name, base_revision, p.revisionExpr)
+                                        f"remove-project name {name}:\n  "
+                                        f"base {base_revision} vs "
+                                        f"revision {p.revisionExpr}"
                                     )
                             del self._paths[p.relpath]
                             if not removed_project:
@@ -1636,13 +1636,9 @@
                             if base_revision:
                                 if p.revisionExpr != base_revision:
                                     failed_revision_changes.append(
-                                        "remove-project path %s mismatch base "
-                                        "%s vs revision %s"
-                                        % (
-                                            p.relpath,
-                                            base_revision,
-                                            p.revisionExpr,
-                                        )
+                                        f"remove-project path {p.relpath}:\n  "
+                                        f"base {base_revision} vs "
+                                        f"revision {p.revisionExpr}"
                                     )
                             self._projects[projname].remove(p)
                             del self._paths[p.relpath]
@@ -1664,10 +1660,10 @@
                     )
 
         if failed_revision_changes:
+            fail_string = "\n".join(failed_revision_changes)
             raise ManifestParseError(
-                "revision base check failed, rebase patches and update "
-                "base revs for: ",
-                failed_revision_changes,
+                f"detected base-revision mismatch, updates needed:\n"
+                f"{fail_string}",
             )
 
         # Store repo hooks project information.