fallow_graph/graph/

mod.rs

//! Module dependency graph with re-export chain propagation and reachability analysis.
//!
//! The graph is built from resolved modules and entry points, then used to determine
//! which files are reachable and which exports are referenced.

mod build;
mod cycles;
mod re_exports;
mod reachability;
pub mod types;

use std::path::PathBuf;

use fixedbitset::FixedBitSet;
use rustc_hash::{FxHashMap, FxHashSet};

use crate::resolve::ResolvedModule;
use fallow_types::discover::{DiscoveredFile, EntryPoint, FileId};
use fallow_types::extract::ImportedName;

// Re-export all public types so downstream sees the same API as before.
pub use types::{ExportSymbol, ModuleNode, ReExportEdge, ReferenceKind, SymbolReference};

/// The core module dependency graph.
#[derive(Debug)]
pub struct ModuleGraph {
    /// All modules indexed by `FileId`.
    pub modules: Vec<ModuleNode>,
    /// Flat edge storage for cache-friendly iteration.
    edges: Vec<Edge>,
    /// Maps npm package names to the set of `FileId`s that import them.
    pub package_usage: FxHashMap<String, Vec<FileId>>,
    /// Maps npm package names to the set of `FileId`s that import them with type-only imports.
    /// A package appearing here but not in `package_usage` (or only in both) indicates
    /// it's only used for types and could be a devDependency.
    pub type_only_package_usage: FxHashMap<String, Vec<FileId>>,
    /// All entry point `FileId`s.
    pub entry_points: FxHashSet<FileId>,
    /// Reverse index: for each `FileId`, which files import it.
    pub reverse_deps: Vec<Vec<FileId>>,
    /// Precomputed: which modules have namespace imports (import * as ns).
    namespace_imported: FixedBitSet,
}

/// An edge in the module graph.
#[derive(Debug)]
pub(super) struct Edge {
    pub(super) source: FileId,
    pub(super) target: FileId,
    pub(super) symbols: Vec<ImportedSymbol>,
}

/// A symbol imported across an edge.
#[derive(Debug)]
pub(super) struct ImportedSymbol {
    pub(super) imported_name: ImportedName,
    pub(super) local_name: String,
    /// Byte span of the import statement in the source file.
    pub(super) import_span: oxc_span::Span,
}

// Size assertions to prevent memory regressions in hot-path graph types.
// `Edge` is stored in a flat contiguous Vec for cache-friendly traversal.
// `ImportedSymbol` is stored in a Vec per Edge.
#[cfg(target_pointer_width = "64")]
const _: () = assert!(std::mem::size_of::<Edge>() == 32);
#[cfg(target_pointer_width = "64")]
const _: () = assert!(std::mem::size_of::<ImportedSymbol>() == 56);

impl ModuleGraph {
    /// Build the module graph from resolved modules and entry points.
    pub fn build(
        resolved_modules: &[ResolvedModule],
        entry_points: &[EntryPoint],
        files: &[DiscoveredFile],
    ) -> Self {
        let _span = tracing::info_span!("build_graph").entered();

        let module_count = files.len();

        // Compute the total capacity needed, accounting for workspace FileIds
        // that may exceed files.len() if IDs are assigned beyond the file count.
        let max_file_id = files
            .iter()
            .map(|f| f.id.0 as usize)
            .max()
            .map_or(0, |m| m + 1);
        let total_capacity = max_file_id.max(module_count);

        // Build path -> FileId index
        let path_to_id: FxHashMap<PathBuf, FileId> =
            files.iter().map(|f| (f.path.clone(), f.id)).collect();

        // Build FileId -> ResolvedModule index
        let module_by_id: FxHashMap<FileId, &ResolvedModule> =
            resolved_modules.iter().map(|m| (m.file_id, m)).collect();

        // Build entry point set — use path_to_id map instead of O(n) scan per entry
        let entry_point_ids: FxHashSet<FileId> = entry_points
            .iter()
            .filter_map(|ep| {
                // Try direct lookup first (fast path)
                path_to_id.get(&ep.path).copied().or_else(|| {
                    // Fallback: canonicalize entry point and do a direct FxHashMap lookup
                    ep.path
                        .canonicalize()
                        .ok()
                        .and_then(|c| path_to_id.get(&c).copied())
                })
            })
            .collect();

        // Phase 1: Build flat edge storage, module nodes, and package usage from resolved modules
        let mut graph = Self::populate_edges(
            files,
            &module_by_id,
            &entry_point_ids,
            module_count,
            total_capacity,
        );

        // Phase 2: Record which files reference which exports (namespace + CSS module narrowing)
        graph.populate_references(&module_by_id, &entry_point_ids);

        // Phase 3: BFS from entry points to mark reachable modules
        graph.mark_reachable(total_capacity);

        // Phase 4: Propagate references through re-export chains
        graph.resolve_re_export_chains();

        graph
    }

    /// Total number of modules.
    pub const fn module_count(&self) -> usize {
        self.modules.len()
    }

    /// Total number of edges.
    pub const fn edge_count(&self) -> usize {
        self.edges.len()
    }

    /// Check if any importer uses `import * as ns` for this module.
    /// Uses precomputed bitset — O(1) lookup.
    pub fn has_namespace_import(&self, file_id: FileId) -> bool {
        let idx = file_id.0 as usize;
        if idx >= self.namespace_imported.len() {
            return false;
        }
        self.namespace_imported.contains(idx)
    }

    /// Get the target `FileId`s of all outgoing edges for a module.
    pub fn edges_for(&self, file_id: FileId) -> Vec<FileId> {
        let idx = file_id.0 as usize;
        if idx >= self.modules.len() {
            return Vec::new();
        }
        let range = &self.modules[idx].edge_range;
        self.edges[range.clone()].iter().map(|e| e.target).collect()
    }

    /// Find the byte offset of the first import statement from `source` to `target`.
    /// Returns `None` if no edge exists or the edge has no symbols.
    pub fn find_import_span_start(&self, source: FileId, target: FileId) -> Option<u32> {
        let idx = source.0 as usize;
        if idx >= self.modules.len() {
            return None;
        }
        let range = &self.modules[idx].edge_range;
        for edge in &self.edges[range.clone()] {
            if edge.target == target {
                return edge.symbols.first().map(|s| s.import_span.start);
            }
        }
        None
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::resolve::{ResolveResult, ResolvedImport, ResolvedModule};
    use fallow_types::discover::{DiscoveredFile, EntryPoint, EntryPointSource, FileId};
    use fallow_types::extract::{ExportName, ImportInfo, ImportedName};
    use std::path::PathBuf;

    // Helper to build a simple module graph
    fn build_simple_graph() -> ModuleGraph {
        // Two files: entry.ts imports foo from utils.ts
        let files = vec![
            DiscoveredFile {
                id: FileId(0),
                path: PathBuf::from("/project/src/entry.ts"),
                size_bytes: 100,
            },
            DiscoveredFile {
                id: FileId(1),
                path: PathBuf::from("/project/src/utils.ts"),
                size_bytes: 50,
            },
        ];

        let entry_points = vec![EntryPoint {
            path: PathBuf::from("/project/src/entry.ts"),
            source: EntryPointSource::PackageJsonMain,
        }];

        let resolved_modules = vec![
            ResolvedModule {
                file_id: FileId(0),
                path: PathBuf::from("/project/src/entry.ts"),
                exports: vec![],
                re_exports: vec![],
                resolved_imports: vec![ResolvedImport {
                    info: ImportInfo {
                        source: "./utils".to_string(),
                        imported_name: ImportedName::Named("foo".to_string()),
                        local_name: "foo".to_string(),
                        is_type_only: false,
                        span: oxc_span::Span::new(0, 10),
                        source_span: oxc_span::Span::default(),
                    },
                    target: ResolveResult::InternalModule(FileId(1)),
                }],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
            ResolvedModule {
                file_id: FileId(1),
                path: PathBuf::from("/project/src/utils.ts"),
                exports: vec![
                    fallow_types::extract::ExportInfo {
                        name: ExportName::Named("foo".to_string()),
                        local_name: Some("foo".to_string()),
                        is_type_only: false,
                        is_public: false,
                        span: oxc_span::Span::new(0, 20),
                        members: vec![],
                    },
                    fallow_types::extract::ExportInfo {
                        name: ExportName::Named("bar".to_string()),
                        local_name: Some("bar".to_string()),
                        is_type_only: false,
                        is_public: false,
                        span: oxc_span::Span::new(25, 45),
                        members: vec![],
                    },
                ],
                re_exports: vec![],
                resolved_imports: vec![],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
        ];

        ModuleGraph::build(&resolved_modules, &entry_points, &files)
    }

    #[test]
    fn graph_module_count() {
        let graph = build_simple_graph();
        assert_eq!(graph.module_count(), 2);
    }

    #[test]
    fn graph_edge_count() {
        let graph = build_simple_graph();
        assert_eq!(graph.edge_count(), 1);
    }

    #[test]
    fn graph_entry_point_is_reachable() {
        let graph = build_simple_graph();
        assert!(graph.modules[0].is_entry_point);
        assert!(graph.modules[0].is_reachable);
    }

    #[test]
    fn graph_imported_module_is_reachable() {
        let graph = build_simple_graph();
        assert!(!graph.modules[1].is_entry_point);
        assert!(graph.modules[1].is_reachable);
    }

    #[test]
    fn graph_export_has_reference() {
        let graph = build_simple_graph();
        let utils = &graph.modules[1];
        let foo_export = utils
            .exports
            .iter()
            .find(|e| e.name.to_string() == "foo")
            .unwrap();
        assert!(
            !foo_export.references.is_empty(),
            "foo should have references"
        );
    }

    #[test]
    fn graph_unused_export_no_reference() {
        let graph = build_simple_graph();
        let utils = &graph.modules[1];
        let bar_export = utils
            .exports
            .iter()
            .find(|e| e.name.to_string() == "bar")
            .unwrap();
        assert!(
            bar_export.references.is_empty(),
            "bar should have no references"
        );
    }

    #[test]
    fn graph_no_namespace_import() {
        let graph = build_simple_graph();
        assert!(!graph.has_namespace_import(FileId(0)));
        assert!(!graph.has_namespace_import(FileId(1)));
    }

    #[test]
    fn graph_has_namespace_import() {
        let files = vec![
            DiscoveredFile {
                id: FileId(0),
                path: PathBuf::from("/project/entry.ts"),
                size_bytes: 100,
            },
            DiscoveredFile {
                id: FileId(1),
                path: PathBuf::from("/project/utils.ts"),
                size_bytes: 50,
            },
        ];

        let entry_points = vec![EntryPoint {
            path: PathBuf::from("/project/entry.ts"),
            source: EntryPointSource::PackageJsonMain,
        }];

        let resolved_modules = vec![
            ResolvedModule {
                file_id: FileId(0),
                path: PathBuf::from("/project/entry.ts"),
                exports: vec![],
                re_exports: vec![],
                resolved_imports: vec![ResolvedImport {
                    info: ImportInfo {
                        source: "./utils".to_string(),
                        imported_name: ImportedName::Namespace,
                        local_name: "utils".to_string(),
                        is_type_only: false,
                        span: oxc_span::Span::new(0, 10),
                        source_span: oxc_span::Span::default(),
                    },
                    target: ResolveResult::InternalModule(FileId(1)),
                }],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
            ResolvedModule {
                file_id: FileId(1),
                path: PathBuf::from("/project/utils.ts"),
                exports: vec![fallow_types::extract::ExportInfo {
                    name: ExportName::Named("foo".to_string()),
                    local_name: Some("foo".to_string()),
                    is_type_only: false,
                    is_public: false,
                    span: oxc_span::Span::new(0, 20),
                    members: vec![],
                }],
                re_exports: vec![],
                resolved_imports: vec![],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
        ];

        let graph = ModuleGraph::build(&resolved_modules, &entry_points, &files);
        assert!(
            graph.has_namespace_import(FileId(1)),
            "utils should have namespace import"
        );
    }

    #[test]
    fn graph_has_namespace_import_out_of_bounds() {
        let graph = build_simple_graph();
        assert!(!graph.has_namespace_import(FileId(999)));
    }

    #[test]
    fn graph_unreachable_module() {
        // Three files: entry imports utils, orphan is not imported
        let files = vec![
            DiscoveredFile {
                id: FileId(0),
                path: PathBuf::from("/project/entry.ts"),
                size_bytes: 100,
            },
            DiscoveredFile {
                id: FileId(1),
                path: PathBuf::from("/project/utils.ts"),
                size_bytes: 50,
            },
            DiscoveredFile {
                id: FileId(2),
                path: PathBuf::from("/project/orphan.ts"),
                size_bytes: 30,
            },
        ];

        let entry_points = vec![EntryPoint {
            path: PathBuf::from("/project/entry.ts"),
            source: EntryPointSource::PackageJsonMain,
        }];

        let resolved_modules = vec![
            ResolvedModule {
                file_id: FileId(0),
                path: PathBuf::from("/project/entry.ts"),
                exports: vec![],
                re_exports: vec![],
                resolved_imports: vec![ResolvedImport {
                    info: ImportInfo {
                        source: "./utils".to_string(),
                        imported_name: ImportedName::Named("foo".to_string()),
                        local_name: "foo".to_string(),
                        is_type_only: false,
                        span: oxc_span::Span::new(0, 10),
                        source_span: oxc_span::Span::default(),
                    },
                    target: ResolveResult::InternalModule(FileId(1)),
                }],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
            ResolvedModule {
                file_id: FileId(1),
                path: PathBuf::from("/project/utils.ts"),
                exports: vec![fallow_types::extract::ExportInfo {
                    name: ExportName::Named("foo".to_string()),
                    local_name: Some("foo".to_string()),
                    is_type_only: false,
                    is_public: false,
                    span: oxc_span::Span::new(0, 20),
                    members: vec![],
                }],
                re_exports: vec![],
                resolved_imports: vec![],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
            ResolvedModule {
                file_id: FileId(2),
                path: PathBuf::from("/project/orphan.ts"),
                exports: vec![fallow_types::extract::ExportInfo {
                    name: ExportName::Named("orphan".to_string()),
                    local_name: Some("orphan".to_string()),
                    is_type_only: false,
                    is_public: false,
                    span: oxc_span::Span::new(0, 20),
                    members: vec![],
                }],
                re_exports: vec![],
                resolved_imports: vec![],
                resolved_dynamic_imports: vec![],
                resolved_dynamic_patterns: vec![],
                member_accesses: vec![],
                whole_object_uses: vec![],
                has_cjs_exports: false,
                unused_import_bindings: vec![],
            },
        ];

        let graph = ModuleGraph::build(&resolved_modules, &entry_points, &files);

        assert!(graph.modules[0].is_reachable, "entry should be reachable");
        assert!(graph.modules[1].is_reachable, "utils should be reachable");
        assert!(
            !graph.modules[2].is_reachable,
            "orphan should NOT be reachable"
        );
    }

    #[test]
    fn graph_package_usage_tracked() {
        let files = vec![DiscoveredFile {
            id: FileId(0),
            path: PathBuf::from("/project/entry.ts"),
            size_bytes: 100,
        }];

        let entry_points = vec![EntryPoint {
            path: PathBuf::from("/project/entry.ts"),
            source: EntryPointSource::PackageJsonMain,
        }];

        let resolved_modules = vec![ResolvedModule {
            file_id: FileId(0),
            path: PathBuf::from("/project/entry.ts"),
            exports: vec![],
            re_exports: vec![],
            resolved_imports: vec![
                ResolvedImport {
                    info: ImportInfo {
                        source: "react".to_string(),
                        imported_name: ImportedName::Default,
                        local_name: "React".to_string(),
                        is_type_only: false,
                        span: oxc_span::Span::new(0, 10),
                        source_span: oxc_span::Span::default(),
                    },
                    target: ResolveResult::NpmPackage("react".to_string()),
                },
                ResolvedImport {
                    info: ImportInfo {
                        source: "lodash".to_string(),
                        imported_name: ImportedName::Named("merge".to_string()),
                        local_name: "merge".to_string(),
                        is_type_only: false,
                        span: oxc_span::Span::new(15, 30),
                        source_span: oxc_span::Span::default(),
                    },
                    target: ResolveResult::NpmPackage("lodash".to_string()),
                },
            ],
            resolved_dynamic_imports: vec![],
            resolved_dynamic_patterns: vec![],
            member_accesses: vec![],
            whole_object_uses: vec![],
            has_cjs_exports: false,
            unused_import_bindings: vec![],
        }];

        let graph = ModuleGraph::build(&resolved_modules, &entry_points, &files);
        assert!(graph.package_usage.contains_key("react"));
        assert!(graph.package_usage.contains_key("lodash"));
        assert!(!graph.package_usage.contains_key("express"));
    }

    #[test]
    fn graph_empty() {
        let graph = ModuleGraph::build(&[], &[], &[]);
        assert_eq!(graph.module_count(), 0);
        assert_eq!(graph.edge_count(), 0);
    }

    #[test]
    fn graph_cjs_exports_tracked() {
        let files = vec![DiscoveredFile {
            id: FileId(0),
            path: PathBuf::from("/project/entry.ts"),
            size_bytes: 100,
        }];

        let entry_points = vec![EntryPoint {
            path: PathBuf::from("/project/entry.ts"),
            source: EntryPointSource::PackageJsonMain,
        }];

        let resolved_modules = vec![ResolvedModule {
            file_id: FileId(0),
            path: PathBuf::from("/project/entry.ts"),
            exports: vec![],
            re_exports: vec![],
            resolved_imports: vec![],
            resolved_dynamic_imports: vec![],
            resolved_dynamic_patterns: vec![],
            member_accesses: vec![],
            whole_object_uses: vec![],
            has_cjs_exports: true,
            unused_import_bindings: vec![],
        }];

        let graph = ModuleGraph::build(&resolved_modules, &entry_points, &files);
        assert!(graph.modules[0].has_cjs_exports);
    }
}