Repository: iterative/dvc
Issue: pipeline: show: outs: improper DAG

See https://discordapp.com/channels/485586884165107732/485586884165107734/557205322641702912 . We should connect outputs to dependencies here https://github.com/iterative/dvc/blob/0.32.1/dvc/command/pipeline.py#L70 instead of connecting all outputs to all outputs of a dependant stage.

Changed files:
dvc/command/pipeline.py, tests/func/test_pipeline.py

diff --git a/dvc/command/pipeline.py b/dvc/command/pipeline.py
index cbec6abf3..510e1feb1 100644
--- a/dvc/command/pipeline.py
+++ b/dvc/command/pipeline.py
@@ -31,45 +31,50 @@ class CmdPipelineShow(CmdBase):
             else:
                 logger.info(stage.path_in_repo)
 
-    def __build_graph(self, target, commands, outs):
+    def _build_graph(self, target, commands, outs):
         import networkx
         from dvc.stage import Stage
         from dvc.repo.graph import get_pipeline
 
-        stage = Stage.load(self.repo, target)
-        G = get_pipeline(self.repo.pipelines, stage)
+        target_stage = Stage.load(self.repo, target)
+        G = get_pipeline(self.repo.pipelines, target_stage)
 
-        nodes = []
-        for stage in G:
+        nodes = set()
+        for stage in networkx.dfs_preorder_nodes(G, target_stage):
             if commands:
                 if stage.cmd is None:
                     continue
-                nodes.append(stage.cmd)
+                nodes.add(stage.cmd)
             elif outs:
                 for out in stage.outs:
-                    nodes.append(str(out))
+                    nodes.add(str(out))
+                for dep in stage.deps:
+                    nodes.add(str(dep))
             else:
-                nodes.append(stage.relpath)
+                nodes.add(stage.relpath)
 
         edges = []
-        for from_stage, to_stage in G.edges():
-            if commands:
-                if to_stage.cmd is None:
-                    continue
-                edges.append((from_stage.cmd, to_stage.cmd))
-            elif outs:
-                for from_out in from_stage.outs:
-                    for to_out in to_stage.outs:
-                        edges.append((str(from_out), str(to_out)))
-            else:
-                edges.append((from_stage.relpath, to_stage.relpath))
 
-        return nodes, edges, networkx.is_tree(G)
+        if outs:
+            for stage in networkx.dfs_preorder_nodes(G, target_stage):
+                for dep in stage.deps:
+                    for out in stage.outs:
+                        edges.append((str(out), str(dep)))
+        else:
+            for from_stage, to_stage in networkx.dfs_edges(G, target_stage):
+                if commands:
+                    if to_stage.cmd is None:
+                        continue
+                    edges.append((from_stage.cmd, to_stage.cmd))
+                else:
+                    edges.append((from_stage.relpath, to_stage.relpath))
+
+        return list(nodes), edges, networkx.is_tree(G)
 
     def _show_ascii(self, target, commands, outs):
         from dvc.dagascii import draw
 
-        nodes, edges, _ = self.__build_graph(target, commands, outs)
+        nodes, edges, _ = self._build_graph(target, commands, outs)
 
         if not nodes:
             return
@@ -79,7 +84,7 @@ class CmdPipelineShow(CmdBase):
     def _show_dependencies_tree(self, target, commands, outs):
         from treelib import Tree
 
-        nodes, edges, is_tree = self.__build_graph(target, commands, outs)
+        nodes, edges, is_tree = self._build_graph(target, commands, outs)
         if not nodes:
             return
         if not is_tree:
@@ -100,12 +105,12 @@ class CmdPipelineShow(CmdBase):
             observe_list.pop(0)
         tree.show()
 
-    def __write_dot(self, target, commands, outs):
+    def _write_dot(self, target, commands, outs):
         import io
         import networkx
         from networkx.drawing.nx_pydot import write_dot
 
-        _, edges, _ = self.__build_graph(target, commands, outs)
+        _, edges, _ = self._build_graph(target, commands, outs)
         edges = [edge[::-1] for edge in edges]
 
         simple_g = networkx.DiGraph()
@@ -126,9 +131,7 @@ class CmdPipelineShow(CmdBase):
                         target, self.args.commands, self.args.outs
                     )
                 elif self.args.dot:
-                    self.__write_dot(
-                        target, self.args.commands, self.args.outs
-                    )
+                    self._write_dot(target, self.args.commands, self.args.outs)
                 elif self.args.tree:
                     self._show_dependencies_tree(
                         target, self.args.commands, self.args.outs
diff --git a/tests/func/test_pipeline.py b/tests/func/test_pipeline.py
index d6420a417..31ed66748 100644
--- a/tests/func/test_pipeline.py
+++ b/tests/func/test_pipeline.py
@@ -1,6 +1,7 @@
 import logging
 
 from dvc.main import main
+from dvc.command.pipeline import CmdPipelineShow
 from tests.basic_env import TestDvc
 from tests.func.test_repro import TestRepro
 from tests.func.test_repro import TestReproChangedDeepData
@@ -98,6 +99,27 @@ class TestPipelineShow(TestRepro):
         self.assertEqual(ret, 0)
 
 
+def test_disconnected_stage(tmp_dir, dvc):
+    tmp_dir.dvc_gen({"base": "base"})
+
+    dvc.add("base")
+    dvc.run(deps=["base"], outs=["derived1"], cmd="echo derived1 > derived1")
+    dvc.run(deps=["base"], outs=["derived2"], cmd="echo derived2 > derived2")
+    final_stage = dvc.run(
+        deps=["derived1"], outs=["final"], cmd="echo final > final"
+    )
+
+    command = CmdPipelineShow([])
+    # Need to test __build_graph directly
+    nodes, edges, is_tree = command._build_graph(
+        final_stage.path, commands=False, outs=True
+    )
+
+    assert set(nodes) == {"final", "derived1", "base"}
+    assert edges == [("final", "derived1"), ("derived1", "base")]
+    assert is_tree is True
+
+
 def test_print_locked_stages(tmp_dir, dvc, caplog):
     tmp_dir.dvc_gen({"foo": "foo content", "bar": "bar content"})
     dvc.lock_stage("foo.dvc")