sbt/notes/2.0.0/dependency-tree-dedup.md at 040eaaa062b5dd20cd2052afa2007bae5d75cf70

luke/sbt

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BrianHotoppandClaude Opus 4.7 3eeac9deae [2.x] fix: Collapse duplicate subtrees in dependency tree rendering (#9226 )

Fixes #6886.

dependencyTree, dependencyBrowseTree, and inspect tree re-explore
the same node once per incoming edge. In a DAG with N levels and M
children per node the rendered output is O(M^N) -- the OP needed
>16 GB heap, #7360 has a 6 GB heap dump, and Friendseeker's analysis
on the issue showed the exponential re-traversal directly.

Fix: track a visited set across the renderer's recursion. The first
time a node is encountered it is rendered in full; on subsequent
visits the entry collapses to a one-line +- <id> (*) (ASCII) or a
<id> (*) leaf (JSON), matching Maven's dependency:tree (*)
convention. Cycle detection (separate parents set, (cycle) marker)
is unchanged.

Co-authored-by: Claude Opus 4.7 (1M context) <[email protected]>

2026-05-18 19:15:47 -04:00

2.2 KiB

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Dependency tree: duplicate-subtree collapse

dependencyTree, dependencyBrowseTree, and inspect tree now collapse duplicate subtrees in a DAG to a single line marked (*), matching the convention used by Maven's dependency:tree. The first occurrence is rendered in full; subsequent occurrences appear as +- <id> (*).

This fixes #6886: rendering a deep diamond DAG no longer produces O(M^N) output (and the OOMs that came with it).

Output change

Before:

o:root_2.13:0.1
  +-o:subA_2.13:0.1 [S]
  | +-o:common_2.13:0.1 [S]
  | | +-org.scala-lang:scala-library:2.13.16 [S]
  | +-org.scala-lang:scala-library:2.13.16 [S]
  +-o:subB_2.13:0.1 [S]
  | +-o:common_2.13:0.1 [S]                          # full subtree again
  | | +-org.scala-lang:scala-library:2.13.16 [S]
  | +-org.scala-lang:scala-library:2.13.16 [S]
  +-org.scala-lang:scala-library:2.13.16 [S]

After:

o:root_2.13:0.1
  +-o:subA_2.13:0.1 [S]
  | +-o:common_2.13:0.1 [S]
  | | +-org.scala-lang:scala-library:2.13.16 [S]
  | +-org.scala-lang:scala-library:2.13.16 [S]
  +-o:subB_2.13:0.1 [S]
  | +-o:common_2.13:0.1 [S] (*)                      # collapsed
  | +-org.scala-lang:scala-library:2.13.16 [S] (*)
  +-org.scala-lang:scala-library:2.13.16 [S] (*)

Affected surfaces

dependencyTree: ASCII output (also dependencyTreeList, dependencyTreeStats).
dependencyBrowseTree: JSON / HTML view.
inspect tree: the setting-graph renderer is the same code path, so the (*) marker shows up there too. Most users don't think of inspect tree as "the dependency tree" -- this note is the heads-up.

Contract for tooling consumers

A line whose entry ends with (*) is a reference to the canonical (first-rendered) occurrence of that node within the same render. Tools parsing dependencyTree / dependencyBrowseTree output should treat <id> (*) as a back-pointer rather than a distinct dependency.

Scope

Dedup is currently within a single root's subtree. Cross-root dedup (when a ModuleGraph has multiple roots that share a transitive closure) is tracked separately as #9227.

2.2 KiB Raw Blame History