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feat(libstore): add detailed cycle detection for build errors
Implements comprehensive cycle detection that shows users exactly which files create circular dependencies when a build fails. This dramatically improves the developer experience when debugging dependency cycles.
This commit is contained in:
Bernardo Meurer Costa
parent
56dbca9a98
commit
e0cbbfbcd2
1 changed files with 169 additions and 38 deletions
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@ -4,7 +4,10 @@
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#include "nix/util/processes.hh"
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#include "nix/store/builtins.hh"
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#include "nix/store/path-references.hh"
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#include "nix/store/dependency-graph.hh"
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#include "nix/util/finally.hh"
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#include <ranges>
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#include "nix/util/util.hh"
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#include "nix/util/archive.hh"
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#include "nix/util/git.hh"
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@ -62,6 +65,103 @@ struct NotDeterministic : BuildError
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}
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};
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/**
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* Information about an output path for cycle analysis.
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*/
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struct OutputPathInfo
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{
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std::string outputName; ///< Name of the output (e.g., "out", "dev")
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StorePath storePath; ///< The StorePath of this output
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Path actualPath; ///< Actual filesystem path where the output is located
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};
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/**
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* Helper to analyze cycles and throw a detailed error.
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*
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* This function always throws - either the detailed cycle error or re-throws
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* the original exception if no cycles are found.
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*
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* @param drvName The formatted name of the derivation being built
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* @param referenceablePaths Set of paths to search for in the outputs
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* @param getOutputPaths Callback returning output information to scan
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*/
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[[noreturn]] static void analyzeCyclesAndThrow(
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std::string_view drvName,
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const StorePathSet & referenceablePaths,
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std::function<std::vector<OutputPathInfo>()> getOutputPaths)
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{
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debug("cycle detected, analyzing for detailed error report");
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// Scan all outputs and build dependency graph
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auto accessor = getFSSourceAccessor();
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DependencyGraph<StorePath, FileListEdgeProperty> depGraph;
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for (auto & output : getOutputPaths()) {
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debug("scanning output '%s' at path '%s' for cycles", output.outputName, output.actualPath);
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auto outputGraph =
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buildStorePathGraphFromScan(*accessor, CanonPath(output.actualPath), output.storePath, referenceablePaths);
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// Merge into combined graph
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for (auto & node : outputGraph.getAllNodes()) {
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for (auto & successor : outputGraph.getSuccessors(node)) {
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auto edgeProp = outputGraph.getEdgeProperty(node, successor);
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if (edgeProp) {
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depGraph.addEdge(node, successor, *edgeProp);
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}
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}
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}
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}
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// Find cycles in the combined graph
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auto cycles = depGraph.findCycles();
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if (cycles.empty()) {
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debug("no detailed cycles found, re-throwing original error");
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throw;
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}
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debug("found %lu cycles", cycles.size());
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// Build detailed error message with file annotations
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std::string cycleDetails = fmt("Detailed cycle analysis found %d cycle path(s):", cycles.size());
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for (const auto & [idx, cycle] : std::views::enumerate(cycles)) {
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cycleDetails += fmt("\n\nCycle %d:", idx + 1);
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for (const auto & window : cycle | std::views::slide(2)) {
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const StorePath & from = window[0];
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const StorePath & to = window[1];
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cycleDetails += fmt("\n → %s", from.to_string());
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// Add file annotations
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auto edgeProp = depGraph.getEdgeProperty(from, to);
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if (edgeProp && !edgeProp->files.empty()) {
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for (const auto & file : edgeProp->files) {
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cycleDetails += fmt("\n (via %s)", file.abs());
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}
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}
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}
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// Close the cycle
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if (!cycle.empty()) {
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cycleDetails += fmt("\n → %s", cycle.back().to_string());
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}
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}
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cycleDetails +=
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fmt("\n\nThis means there are circular references between output files.\n"
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"The build cannot proceed because the outputs reference each other.");
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// Add hint with temp paths for debugging
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if (settings.keepFailed || verbosity >= lvlDebug) {
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cycleDetails += "\n\nNote: Temporary build outputs are preserved for inspection.";
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}
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throw BuildError(
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BuildResult::Failure::OutputRejected, "cycle detected in build of '%s': %s", drvName, cycleDetails);
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}
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/**
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* This class represents the state for building locally.
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*
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@ -1473,43 +1573,62 @@ SingleDrvOutputs DerivationBuilderImpl::registerOutputs()
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outputStats.insert_or_assign(outputName, std::move(st));
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}
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auto sortedOutputNames = topoSort(
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outputsToSort,
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{[&](const std::string & name) {
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auto orifu = get(outputReferencesIfUnregistered, name);
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if (!orifu)
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throw BuildError(
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BuildResult::Failure::OutputRejected,
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"no output reference for '%s' in build of '%s'",
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name,
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store.printStorePath(drvPath));
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return std::visit(
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overloaded{
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/* Since we'll use the already installed versions of these, we
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can treat them as leaves and ignore any references they
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have. */
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[&](const AlreadyRegistered &) { return StringSet{}; },
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[&](const PerhapsNeedToRegister & refs) {
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StringSet referencedOutputs;
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/* FIXME build inverted map up front so no quadratic waste here */
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for (auto & r : refs.refs)
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for (auto & [o, p] : scratchOutputs)
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if (r == p)
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referencedOutputs.insert(o);
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return referencedOutputs;
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},
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},
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*orifu);
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}},
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{[&](const std::string & path, const std::string & parent) {
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// TODO with more -vvvv also show the temporary paths for manual inspection.
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return BuildError(
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BuildResult::Failure::OutputRejected,
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"cycle detected in build of '%s' in the references of output '%s' from output '%s'",
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store.printStorePath(drvPath),
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path,
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parent);
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}});
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auto sortedOutputNames = [&]() {
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try {
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return topoSort(
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outputsToSort,
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{[&](const std::string & name) {
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auto orifu = get(outputReferencesIfUnregistered, name);
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if (!orifu)
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throw BuildError(
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BuildResult::Failure::OutputRejected,
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"no output reference for '%s' in build of '%s'",
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name,
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store.printStorePath(drvPath));
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return std::visit(
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overloaded{
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/* Since we'll use the already installed versions of these, we
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can treat them as leaves and ignore any references they
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have. */
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[&](const AlreadyRegistered &) { return StringSet{}; },
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[&](const PerhapsNeedToRegister & refs) {
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StringSet referencedOutputs;
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/* FIXME build inverted map up front so no quadratic waste here */
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for (auto & r : refs.refs)
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for (auto & [o, p] : scratchOutputs)
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if (r == p)
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referencedOutputs.insert(o);
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return referencedOutputs;
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},
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},
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*orifu);
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}},
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{[&](const std::string & path, const std::string & parent) {
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// TODO with more -vvvv also show the temporary paths for manual inspection.
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return BuildError(
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BuildResult::Failure::OutputRejected,
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"cycle detected in build of '%s' in the references of output '%s' from output '%s'",
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store.printStorePath(drvPath),
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path,
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parent);
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}});
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} catch (std::exception & e) {
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analyzeCyclesAndThrow(store.printStorePath(drvPath), referenceablePaths, [&]() {
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std::vector<OutputPathInfo> outputPaths;
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for (auto & [outputName, _] : drv.outputs) {
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auto scratchOutput = get(scratchOutputs, outputName);
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if (scratchOutput) {
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outputPaths.push_back(
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OutputPathInfo{
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.outputName = outputName,
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.storePath = *scratchOutput,
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.actualPath = realPathInSandbox(store.printStorePath(*scratchOutput))});
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}
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}
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return outputPaths;
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});
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}
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}();
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std::reverse(sortedOutputNames.begin(), sortedOutputNames.end());
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@ -1848,12 +1967,24 @@ SingleDrvOutputs DerivationBuilderImpl::registerOutputs()
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/* Register each output path as valid, and register the sets of
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paths referenced by each of them. If there are cycles in the
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outputs, this will fail. */
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{
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try {
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ValidPathInfos infos2;
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for (auto & [outputName, newInfo] : infos) {
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infos2.insert_or_assign(newInfo.path, newInfo);
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}
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store.registerValidPaths(infos2);
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} catch (BuildError & e) {
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analyzeCyclesAndThrow(store.printStorePath(drvPath), referenceablePaths, [&]() {
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std::vector<OutputPathInfo> outputPaths;
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for (auto & [outputName, newInfo] : infos) {
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outputPaths.push_back(
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OutputPathInfo{
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.outputName = outputName,
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.storePath = newInfo.path,
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.actualPath = store.toRealPath(store.printStorePath(newInfo.path))});
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}
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return outputPaths;
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});
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}
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/* If we made it this far, we are sure the output matches the
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