Fix query-failure fallback for bzlmod-only workspaces

The unioned rdeps query-failure fallback filtered out every `@@` label
on the assumption that the hash set was mostly workspace-local `//...`
targets. That assumption does not hold on bzlmod-only workspaces where
`generate-hashes` emits almost entirely `@@canonical` labels plus a
small number of `//external:<apparent>` bzlmod-synthetic bridges, with
zero workspace-local targets.

On such workspaces, a query failure (for example, one caused by an
unrelated loading error elsewhere in the dep graph) left the filter
with only the `//external:*` bridges, which the downstream
`excludeExternalTargets=true` default (Tinder#334) then strips entirely —
producing silently-empty impacted output on what should be a
"conservatively rebuild everything" signal.

Mark every hashed target as impacted on query failure. Downstream
filters (`targetTypes`, `excludeExternalTargets`) remain the caller's
responsibility, which is the whole point of surfacing the full set
upstream.

Add a regression test that constructs a bzlmod-shaped hash set (two
`@@abseil-cpp+` targets + one `//external:*` bridge, no workspace
targets), stubs `queryService.query` to throw, and asserts all three
labels appear in the output.

Author: rdark

cli/src/main/kotlin/com/bazel_diff/interactor/CalculateImpactedTargetsInteractor.kt

@@ -373,8 +373,16 @@ class CalculateImpactedTargetsInteractor : KoinComponent {
         logger.i { "Found ${rdepLabels.size} workspace targets depending on changed modules" }
         impactedTargets.addAll(rdepLabels)
       } catch (e: Exception) {
-        logger.e(e) { "Unioned rdeps query failed - conservatively marking all workspace targets impacted" }
-        impactedTargets.addAll(allTargets.keys.filter { !it.startsWith("@@") })
+        logger.e(e) { "Unioned rdeps query failed - conservatively marking all targets impacted" }
+        // Mark every hashed target as impacted. Filtering out `@@` labels would
+        // produce silently-empty output on bzlmod-only workspaces where the hash
+        // set is almost entirely `@@canonical` + `//external:<apparent>` bridges
+        // with zero workspace-local `//...` targets; the downstream
+        // `excludeExternalTargets=true` default (#334) would then strip the
+        // remaining `//external:*`, leaving nothing. Downstream filters
+        // (`targetTypes`, `excludeExternalTargets`) remain the caller's
+        // responsibility.
+        impactedTargets.addAll(allTargets.keys)
       }
     }
 

cli/src/test/kotlin/com/bazel_diff/interactor/CalculateImpactedTargetsInteractorModuleQueryTest.kt

@@ -328,6 +328,43 @@ class CalculateImpactedTargetsInteractorModuleQueryTest : KoinTest {
     assertThat(queryCaptor.firstValue).contains("@@abseil-cpp+//...")
   } }
 
+  @Test
+  fun queryFailureMarksAllHashedTargetsImpactedIncludingExternal() { runBlocking {
+    // On bzlmod-only workspaces the hash set is almost entirely `@@canonical`
+    // and `//external:<apparent>` bridges with zero workspace-local `//...`
+    // targets. If the unioned rdeps query fails, the conservative fallback
+    // must still surface a non-empty impacted set — otherwise the downstream
+    // `excludeExternalTargets=true` default strips the only remaining labels
+    // and the CLI reports zero impacted targets on what is really a
+    // "rebuild everything" condition.
+    val hashes = mapOf(
+        "@@abseil-cpp+//absl:strings" to TargetHash("Rule", "a", "a"),
+        "@@abseil-cpp+//absl:base" to TargetHash("Rule", "b", "b"),
+        "//external:com_google_absl" to TargetHash("Rule", "c", "c"))
+
+    whenever(queryService.discoverRepoMapping())
+        .thenReturn(mapOf("abseil-cpp" to "abseil-cpp+"))
+    whenever(queryService.query(any(), any()))
+        .thenThrow(RuntimeException("simulated bazel query failure"))
+
+    val writer = StringWriter()
+    CalculateImpactedTargetsInteractor().execute(
+        from = hashes,
+        to = hashes,
+        outputWriter = writer,
+        targetTypes = null,
+        fromModuleGraphJson = graph("abseil-cpp", "20240116.2"),
+        toModuleGraphJson = graph("abseil-cpp", "20240722.0"))
+
+    // Every hashed label must appear in the fallback output, including `@@`
+    // and `//external:*`. Downstream filters (targetTypes, excludeExternalTargets)
+    // are the caller's responsibility.
+    assertThat(outputLines(writer)).containsExactlyInAnyOrder(
+        "@@abseil-cpp+//absl:strings",
+        "@@abseil-cpp+//absl:base",
+        "//external:com_google_absl")
+  } }
+
   @Test
   fun executeWithDistancesRunsModuleQueryPath() { runBlocking {
     // Covers the parallel module-query call site in `executeWithDistances`.