@@ -14,6 +14,10 @@ pkgdev 0.2.19 (unreleased)
 - bugs: fix a package being filed as its own dependency, when an unsolvable
   ``|| ( ... )`` is answered by the package's own slot (Arthur Zamarin, #208)
 
+- bugs: add ``--dry-run``, printing the bugs which would be filed and the
+  updates to existing bugs instead of sending them. It needs no API key
+  (Arthur Zamarin)
+
 **pkgdev commit:**
 
 - commit: a path argument sharing its name with a ref, e.g. ``pkgdev commit
 
@@ -282,6 +282,7 @@ _pkgdev() {
         bugs)
             subcmd_options="
                 --api-key
+                --dry-run
                 --edit-graph
                 --auto-cc-arches
                 --find-by-maintainer
 
@@ -144,6 +144,7 @@ case $state in
           $base_options \
           '--api-key[Bugzilla API key]:api key' \
           '--dot[path file where to save the graph in dot format]:file:_files' \
+          '--dry-run[print the bugs instead of filing them]' \
           '--edit-graph[open editor to modify the graph before filing bugs]' \
           '--auto-cc-arches[automatically add CC-ARCHES for listed email addresses]:emails' \
           '--find-by-maintainer[collect all packages maintained by listed email addresses]:emails' \
 
@@ -1,6 +1,7 @@
 """Automatic bugs filer"""
 
 import contextlib
+import dataclasses
 import os
 import shlex
 import subprocess
@@ -11,7 +12,7 @@
 from collections import defaultdict
 from datetime import UTC, datetime
 from functools import partial
-from itertools import chain
+from itertools import chain, count
 from os.path import join as pjoin
 from typing import Literal
 
@@ -158,6 +159,17 @@ def __call__(self, parser, namespace, values, option_string=None):
     "--dot",
     help="path file where to save the graph in dot format",
 )
+bugs.add_argument(
+    "--dry-run",
+    action="store_true",
+    help="print the bugs instead of filing them",
+    docs="""
+        Do everything up to filing, including searching for open bugs, but
+        print the bugs which would be filed and the updates to existing bugs,
+        instead of sending them to Bugzilla. Bugs not yet filed are numbered
+        ``new-1``, ``new-2``, ... in the output. No API key is required.
+    """,
+)
 bugs.add_argument(
     "--edit-graph",
     action="store_true",
@@ -304,6 +316,69 @@ def _naming(what: str):
         raise BugzillaError(f"{what}: {exc}") from exc
 
 
+class DryRunBugzilla:
+    """Bugzilla client which searches as usual, but prints any change instead."""
+
+    def __init__(self, bugzilla: Bugzilla, out: Formatter):
+        self.bugzilla = bugzilla
+        self.out = out
+        self._new_ids = (f"new-{i}" for i in count(1))
+
+    def search(self, query: BugQuery):
+        return self.bugzilla.search(query)
+
+    def _field(self, name: str, value):
+        if value:
+            self.out.write(f"  {name + ':':<12}{value}")
+
+    def create(self, bug: NewBug) -> str:
+        bugno = next(self._new_ids)
+        out = self.out
+        out.write(out.fg("green"), f"Would file {bugno}: ", out.reset, bug.summary)
+        self._field("component", f"{bug.product} / {bug.component}")
+        self._field("assignee", bug.assigned_to)
+        self._field("CC", ", ".join(bug.cc))
+        self._field("keywords", ", ".join(bug.keywords))
+        self._field("depends on", ", ".join(sorted(map(str, bug.depends_on))))
+        self._field("blocks", ", ".join(sorted(map(str, bug.blocks))))
+        out.write("  packages:")
+        for line in str(bug.package_list).splitlines():
+            out.write(f"    {line}")
+        out.write("  description:")
+        for line in bug.description.splitlines():
+            out.write(f"    {line}".rstrip())
+        out.write()
+        out.flush()
+        return bugno
+
+    def update(self, bugs, update: BugUpdate):
+        ids = [bugs] if isinstance(bugs, int) else list(bugs)
+        out = self.out
+        out.write(
+            out.fg("yellow"),
+            "Would update bugs " if len(ids) > 1 else "Would update bug ",
+            out.reset,
+            ", ".join(map(str, ids)),
+        )
+        for field in dataclasses.fields(update):
+            value = getattr(update, field.name)
+            if isinstance(value, ListChange):
+                value = " ".join(
+                    chain(
+                        (f"+{x}" for x in value.add),
+                        (f"-{x}" for x in value.remove),
+                        (f"={x}" for x in value.replace or ()),
+                    )
+                )
+            elif isinstance(value, tuple):
+                value = ", ".join(map(str, value))
+            elif value is not None:
+                value = str(value)
+            self._field(field.name.replace("_", " "), value)
+        out.write()
+        out.flush()
+
+
 class GraphNode:
     __slots__ = ("bugno", "category", "cc_arches", "edges", "obsoletes", "pkgs", "summary")
 
@@ -1184,8 +1259,9 @@ def observe(node: GraphNode):
             )
             self.out.flush()
 
+        observer = None if isinstance(bugzilla, DryRunBugzilla) else observe
         for node in self.starting_nodes:
-            node.file_bug(bugzilla, auto_cc_arches, block_bugs, self.modified_repo, observe)
+            node.file_bug(bugzilla, auto_cc_arches, block_bugs, self.modified_repo, observer)
         self.obsolete_bugs(bugzilla)
 
     def obsolete_bugs(self, bugzilla: Bugzilla):
@@ -1210,7 +1286,9 @@ def _load_from_stdin(out: Formatter):
 
 @bugs.bind_main_func
 def main(options, out: Formatter, err: Formatter):
-    if options.api_key is None:
+    if options.dry_run:
+        options.bugzilla = DryRunBugzilla(options.bugzilla, out)
+    elif options.api_key is None:
         err.write(out.fg("red"), "No API key provided, exiting", out.reset)
         return 1
 
@@ -1286,11 +1364,14 @@ def main(options, out: Formatter, err: Formatter):
     pending = [node for node in d.nodes if node.bugno is None]
     if not pending:
         # no bugs to file, but obsoletions of matched bugs may still be pending
-        if (obsoletes := {bugno for node in d.nodes for bugno in node.obsoletes}) and userquery(
-            f"No bugs to file, still obsolete {len(obsoletes)} bugs?",
-            out,
-            err,
-            default_answer=False,
+        if (obsoletes := {bugno for node in d.nodes for bugno in node.obsoletes}) and (
+            options.dry_run
+            or userquery(
+                f"No bugs to file, still obsolete {len(obsoletes)} bugs?",
+                out,
+                err,
+                default_answer=False,
+            )
         ):
             d.obsolete_bugs(options.bugzilla)
             return 0
@@ -1302,7 +1383,9 @@ def main(options, out: Formatter, err: Formatter):
     }
     summary = ", ".join(f"{count} {suffix}" for suffix, count in counts.items() if count)
 
-    if not userquery(
+    if options.dry_run:
+        out.write(f"Dry run, would create {len(pending)} bugs ({summary}):\n")
+    elif not userquery(
         f"Continue and create {len(pending)} bugs ({summary})?", out, err, default_answer=False
     ):
         return 1
 
@@ -1218,3 +1218,46 @@ def test_bugs_are_filed(self, repo, bugs_options, bugzilla_cassette, monkeypatch
         create = bugzilla_cassette.calls[-1].body
         assert create["summary"] == "cat/a-2: stablereq"
         assert create["cf_stabilisation_atoms"] == "=cat/a-2 *"
+
+    def test_dry_run_files_nothing(self, repo, bugs_options, bugzilla_cassette, monkeypatch):
+        self.mk_target(repo)
+        set_userquery(monkeypatch, yesno=True)
+        bugzilla_cassette.expect_bugs()
+        out = mk_out()
+        # no api key needed, searching is read only
+        bugs.main(bugs_options("--dry-run", "=cat/a-2"), out, out)
+
+        assert [call.method for call in bugzilla_cassette.calls] == ["GET"]
+        assert "Would file new-1: cat/a-2: stablereq" in out.lines
+        assert "  component:  Gentoo Linux / Stabilization" in out.lines
+        assert "    =cat/a-2 *" in out.lines
+
+
+def test_dry_run_prints_new_bugs_and_updates(repo, bugzilla_cassette):
+    mk_repo(repo)
+    pkgU = max(repo.itermatch(atom("=cat/u-0")))
+    pkgX = max(repo.itermatch(atom("=cat/x-0")))
+    pkgY = max(repo.itermatch(atom("=cat/y-0")))
+    node = bugs.GraphNode((), bugno=200)
+    dep = bugs.GraphNode(((pkgX, {"*"}), (pkgY, {"*"})))
+    dep.edges.add(bugs.GraphNode(((pkgU, {"*"}),)))
+    dep.obsoletes.add(100)
+    node.edges.add(dep)
+
+    out = mk_out()
+    dry_run = bugs.DryRunBugzilla(bugzilla_cassette.client(), out)
+    assert node.file_bug(dry_run, frozenset(), (), None) == 200
+    assert bugzilla_cassette.calls == []
+    assert dep.bugno == "new-2"
+
+    lines = out.lines
+    assert "Would file new-1: cat/u-0: stablereq" in lines
+    assert "Would file new-2: cat/x-0, cat/y-0: stablereq" in lines
+    assert "  assignee:   dev3@gentoo.org" in lines
+    assert "  CC:         dev1@gentoo.org" in lines
+    assert "  depends on: new-1" in lines
+    assert "Would update bug 100" in lines
+    assert "  resolution: OBSOLETE" in lines
+    assert "  see also:   +https://bugs.gentoo.org/new-2" in lines
+    assert "Would update bug 200" in lines
+    assert "  depends on: +new-2" in lines