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Optimize library cycle loader. #4281

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Merged
merged 1 commit into from
Nov 14, 2025
Merged

Optimize library cycle loader. #4281

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2 changes: 2 additions & 0 deletions build_runner/CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
## 2.10.3-wip

- Performance: improve scalability with the number of library cycles, making
builds much faster for some large codebases.
- Bug fix: fix crash when you run `dart run build_runner build` in a
subdirectory of a package.
- Bug fix: in a workspace, generate for transitive dependencies of the current
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21 changes: 9 additions & 12 deletions build_runner/lib/src/build/library_cycle_graph/library_cycle_graph_loader.dart
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Expand Up @@ -341,24 +341,21 @@ class LibraryCycleGraphLoader {
///
/// A [_graphs] entry will be created for each ID in [newCycles].
void _buildGraphs(int phase, {required List<LibraryCycle> newCycles}) {
// Build lookup from ID to [LibraryCycle] including new and existing cycles.
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@jensjoha jensjoha Nov 14, 2025

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Am I reading this right, that this boils down to not pre-populating the map?

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@davidmorgan davidmorgan Nov 14, 2025

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Yes, exactly :)

final existingCycles = <LibraryCycle>[];
for (final phasedCycle in _cycles.values) {
if (phasedCycle.isExpiredAt(phase: phase)) continue;
existingCycles.add(phasedCycle.valueAt(phase: phase));
}
// Cycles by ID at the current phase.
final cycleById = <AssetId, LibraryCycle>{};
for (final cycle in existingCycles) {
for (final id in cycle.ids) {
cycleById[id] = cycle;
}
}
for (final cycle in newCycles) {
for (final id in cycle.ids) {
cycleById[id] = cycle;
}
}

/// Lookups up [id] in [cycleById], falling back to [_cycles] if it's not
/// present.
LibraryCycle lookupLibraryCycle(AssetId id) =>
cycleById.putIfAbsent(id, () {
return _cycles[id]!.valueAt(phase: phase);
});

// Create the graph for each cycle in [newCycles].
for (final root in newCycles) {
final graph = LibraryCycleGraphBuilder()..root.replace(root);
Expand All @@ -379,7 +376,7 @@ class LibraryCycleGraphLoader {
for (final id in root.ids) {
final assetDeps = _assetDeps[id]!.valueAt(phase: phase);
for (final dep in assetDeps.deps) {
final depCycle = cycleById[dep]!;
final depCycle = lookupLibraryCycle(dep);
if (identical(depCycle, root)) continue;
if (alreadyAddedChildren.add(depCycle)) {
final childGraph = _graphs[dep]!.expiringValueAt(phase: phase);
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