showing message only once

src/pip/_internal/resolution/resolvelib/reporter.py

@@ -20,8 +20,9 @@ class PipReporter(BaseReporter):
     def __init__(
         self, conflicts_message_generator: Callable[[Causes], Optional[str]]
     ) -> None:
-        self.backtracks_by_package: DefaultDict[str, int] = defaultdict(int)
         self.conflicts_message_generator = conflicts_message_generator
+        self.resolved_conflicts = False
+        self.backtracks_by_package: DefaultDict[str, int] = defaultdict(int)
 
         self._messages_at_backtrack = {
             1: (
@@ -53,7 +54,9 @@ def backtracking(self, candidate: Candidate) -> None:
         logger.info("INFO: %s", message.format(package_name=candidate.name))
 
     def resolving_conflicts(self, causes: Any) -> None:
-        logger.info("INFO: %s", self.conflicts_message_generator(causes))
+        if not self.resolved_conflicts:
+            self.resolved_conflicts = True
+            logger.info("INFO: %s", self.conflicts_message_generator(causes))
 
 
 class PipDebuggingReporter(BaseReporter):

tests/functional/test_new_resolver.py

@@ -1163,13 +1163,26 @@ def test_new_resolver_presents_messages_when_backtracking_a_lot(script, N):
         assert "press Ctrl + C" in result.stdout
 
 
-def test_new_resolver_presents_messages_when_resolving_conflicts(script):
+def test_new_resolver_presents_conflicts_when_resolving_conflicts_for_the_first_time(
+    script,
+):
+    def conflict_message(v):
+        return (
+            f"INFO: Cannot install a=={v}.0.0 and b==1.0.0 "
+            f"because these package versions have conflicting dependencies.\n"
+            f"The conflict is caused by:\n"
+            f"    a {v}.0.0 depends on c=={v}.0.0\n"
+            f"    b 1.0.0 depends on c==1.0.0"
+        )
+
     packages = [
+        ("a", "3.0.0", ["c==3.0.0"]),
         ("a", "2.0.0", ["c==2.0.0"]),
         ("a", "1.0.0", ["c==1.0.0"]),
         ("b", "1.0.0", ["c==1.0.0"]),
         ("c", "1.0.0", []),
         ("c", "2.0.0", []),
+        ("c", "3.0.0", []),
     ]
 
     for name, version, depends in packages:
@@ -1187,15 +1200,12 @@ def test_new_resolver_presents_messages_when_resolving_conflicts(script):
     )
 
     script.assert_installed(A="1.0.0", B="1.0.0", C="1.0.0")
-    message = (
-        "INFO: Cannot install a==2.0.0 and b==1.0.0 "
-        "because these package versions have conflicting dependencies.\n"
-        "The conflict is caused by:\n"
-        "    a 2.0.0 depends on c==2.0.0\n"
-        "    b 1.0.0 depends on c==1.0.0"
-    )
+    first_message = conflict_message(3)
+    second_message = conflict_message(2)
+
     stdout = result.stdout
-    assert message in stdout
+    assert first_message in stdout
+    assert second_message not in stdout
 
 
 @pytest.mark.parametrize(