+// SPDX-FileCopyrightText: 2026 Nikolay Govorov

+// SPDX-License-Identifier: AGPL-3.0-or-later

+//

+// The approach to gathering licenses — resolving the dependency graph via

+// krates, scanning crate sources for license texts with spdx detection,

+// and deduplicating results — is based on cargo-about

+// (https://github.com/EmbarkStudios/cargo-about) by Embark Studios,

+// licensed under MIT OR Apache-2.0.

+

+use std::collections::BTreeMap;

+use std::{cmp, fmt};

+

+use krates::cm;

+use krates::{Utf8Path, Utf8PathBuf};

+use serde::Serialize;

+use spdx::detection as sd;

+use spdx::{Expression, LicenseReq, Licensee};

+

+const CONFIDENCE_THRESHOLD: f32 = 0.8;

+

+const IGNORE_PRIVATE: bool = true;

+const IGNORE_DEV_DEPENDENCIES: bool = true;

+const IGNORE_BUILD_DEPENDENCIES: bool = true;

+const IGNORE_TRANSITIVE_DEPENDENCIES: bool = false;

+

+struct Crate(cm::Package);

+

+impl Crate {

+ fn get_license_expression(&self) -> LicenseInfo {

+ if let Some(license_field) = &self.0.license {

+ match Crate::parse_license_expression(license_field) {

+ Ok(validated) => LicenseInfo::Expr(validated),

+ Err(err) => {

+ tracing::error!("unable to parse license expression for '{self}': {err}");

+ LicenseInfo::Unknown

+ }

+ }

+ } else {

+ tracing::warn!("crate '{self}' doesn't have a license field");

+ LicenseInfo::Unknown

+ }

+ }

+

+ fn parse_license_expression(license: &str) -> Result<Expression, spdx::ParseError> {

+ Expression::parse_mode(

+ license,

+ spdx::ParseMode {

+ allow_deprecated: true,

+ allow_imprecise_license_names: true,

+ allow_slash_as_or_operator: false,

+ allow_postfix_plus_on_gpl: true,

+ allow_unknown: false,

+ },

+ )

+ }

+}

+

+impl Ord for Crate {

+ fn cmp(&self, o: &Self) -> cmp::Ordering {

+ match self.0.name.cmp(&o.0.name) {

+ cmp::Ordering::Equal => self.0.version.cmp(&o.0.version),

+ o => o,

+ }

+ }

+}

+

+impl PartialOrd for Crate {

+ fn partial_cmp(&self, o: &Self) -> Option<cmp::Ordering> {

+ Some(self.cmp(o))

+ }

+}

+

+impl Eq for Crate {}

+

+impl PartialEq for Crate {

+ fn eq(&self, o: &Self) -> bool {

+ self.cmp(o) == cmp::Ordering::Equal

+ }

+}

+

+impl From<cm::Package> for Crate {

+ fn from(mut pkg: cm::Package) -> Self {

+ // Fix the license field as cargo used to allow the invalid / separator

+ if let Some(lf) = &mut pkg.license {

+ *lf = lf.replace('/', " OR ");

+ }

+

+ Self(pkg)

+ }

+}

+

+impl krates::KrateDetails for Crate {

+ fn name(&self) -> &str {

+ &self.0.name

+ }

+

+ fn version(&self) -> &krates::semver::Version {

+ &self.0.version

+ }

+}

+

+impl fmt::Display for Crate {

+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

+ write!(f, "{} {}", self.0.name, self.0.version)

+ }

+}

+

+impl std::ops::Deref for Crate {

+ type Target = cm::Package;

+

+ fn deref(&self) -> &Self::Target {

+ &self.0

+ }

+}

+

+type Krates = krates::Krates<Crate>;

+

+fn get_all_crates(cargo_toml: &Utf8Path) -> Result<Krates, krates::Error> {

+ let mut mdc = krates::Cmd::new();

+ mdc.manifest_path(cargo_toml);

+

+ let mut builder = krates::Builder::new();

+

+ if IGNORE_BUILD_DEPENDENCIES {

+ builder.ignore_kind(krates::DepKind::Build, krates::Scope::All);

+ }

+

+ if IGNORE_DEV_DEPENDENCIES {

+ builder.ignore_kind(krates::DepKind::Dev, krates::Scope::All);

+ }

+

+ if IGNORE_TRANSITIVE_DEPENDENCIES {

+ builder.ignore_kind(krates::DepKind::Normal, krates::Scope::NonWorkspace);

+ builder.ignore_kind(krates::DepKind::Dev, krates::Scope::NonWorkspace);

+ builder.ignore_kind(krates::DepKind::Build, krates::Scope::NonWorkspace);

+ }

+

+ builder.include_targets(std::iter::once((env!("TARGET"), vec![])));

+

+ let graph = builder.build(mdc, |filtered: cm::Package| {

+ tracing::debug!("filtered {} {}", filtered.name, filtered.version);

+ })?;

+

+ Ok(graph)

+}

+

+type LicenseStore = sd::Store;

+

+fn load_license_store() -> Result<LicenseStore, Box<dyn std::error::Error>> {

+ Ok(sd::Store::load_inline()?)

+}

+

+#[derive(Debug)]

+#[allow(clippy::large_enum_variant)]

+enum LicenseInfo {

+ Expr(Expression),

+ Unknown,

+}

+

+enum LicenseFileKind {

+ /// The license file is the canonical text of the license

+ Text(String),

+ /// The file just has a license header

+ Header,

+}

+

+struct LicenseFile {

+ license_expr: Expression,

+ confidence: f32,

+ kind: LicenseFileKind,

+}

+

+impl Ord for LicenseFile {

+ fn cmp(&self, o: &Self) -> cmp::Ordering {

+ match self.license_expr.as_ref().cmp(o.license_expr.as_ref()) {

+ cmp::Ordering::Equal => o

+ .confidence

+ .partial_cmp(&self.confidence)

+ .expect("NaN encountered comparing license confidences"),

+ ord => ord,

+ }

+ }

+}

+

+impl PartialOrd for LicenseFile {

+ fn partial_cmp(&self, o: &Self) -> Option<cmp::Ordering> {

+ Some(self.cmp(o))

+ }

+}

+

+impl PartialEq for LicenseFile {

+ fn eq(&self, o: &Self) -> bool {

+ self.cmp(o) == cmp::Ordering::Equal

+ }

+}

+

+impl Eq for LicenseFile {}

+

+struct KrateLicense<'krate> {

+ krate: &'krate Crate,

+ lic_info: LicenseInfo,

+ license_files: Vec<LicenseFile>,

+}

+

+fn walk_files(dir: &Utf8Path) -> Vec<Utf8PathBuf> {

+ let mut files = Vec::new();

+ let mut stack = vec![dir.to_path_buf()];

+

+ while let Some(current) = stack.pop() {

+ let entries = match std::fs::read_dir(&current) {

+ Ok(entries) => entries,

+ Err(e) => {

+ tracing::warn!("failed to read directory '{current}': {e}");

+ continue;

+ }

+ };

+

+ for entry in entries.filter_map(|e| e.ok()) {

+ let ft = match entry.file_type() {

+ Ok(ft) => ft,

+ Err(_) => continue,

+ };

+

+ let path = match Utf8PathBuf::from_path_buf(entry.path()) {

+ Ok(pb) => pb,

+ Err(e) => {

+ tracing::warn!("skipping path {}, not a valid utf-8 path", e.display());

+ continue;

+ }

+ };

+

+ if ft.is_dir() {

+ stack.push(path);

+ } else if ft.is_file() {

+ files.push(path);

+ }

+ }

+ }

+

+ files

+}

+

+fn scan_files(

+ root_dir: &Utf8Path,

+ scanner: &sd::scan::Scanner<'_>,

+ threshold: f32,

+) -> Vec<LicenseFile> {

+ walk_files(root_dir)

+ .into_iter()

+ .filter_map(|path| {

+ let contents = read_file(&path)?;

+ check_is_license_file(path, contents, scanner, threshold)

+ })

+ .collect()

+}

+

+fn read_file(path: &Utf8Path) -> Option<String> {

+ match std::fs::read_to_string(path) {

+ Err(ref e) if e.kind() == std::io::ErrorKind::InvalidData => {

+ tracing::debug!("binary file '{path}' detected");

+ None

+ }

+ Err(e) => {

+ tracing::error!("failed to read '{path}': {e}");

+ None

+ }

+ Ok(c) => Some(c),

+ }

+}

+

+fn check_is_license_file(

+ path: Utf8PathBuf,

+ contents: String,

+ scanner: &sd::scan::Scanner<'_>,

+ threshold: f32,

+) -> Option<LicenseFile> {

+ match scan_text(&contents, scanner, threshold) {

+ ScanResult::Header(ided) => {

+ let license_expr = match Expression::parse(ided.id.name) {

+ Ok(expr) => expr,

+ Err(err) => {

+ tracing::error!(

+ "failed to parse license '{}' at {path:?} into a valid expression: {err}",

+ ided.id.name

+ );

+ return None;

+ }

+ };

+

+ Some(LicenseFile {

+ license_expr,

+ confidence: ided.confidence,

+ kind: LicenseFileKind::Header,

+ })

+ }

+ ScanResult::Text(ided) => {

+ let license_expr = match Expression::parse(ided.id.name) {

+ Ok(expr) => expr,

+ Err(err) => {

+ tracing::error!(

+ "failed to parse license '{}' at {path:?} into a valid expression: {err}",

+ ided.id.name

+ );

+ return None;

+ }

+ };

+

+ Some(LicenseFile {

+ license_expr,

+ confidence: ided.confidence,

+ kind: LicenseFileKind::Text(contents),

+ })

+ }

+ ScanResult::UnknownId(id_str) => {

+ tracing::error!("found unknown SPDX identifier '{id_str}' scanning '{path}'");

+ None

+ }

+ ScanResult::LowLicenseChance(ided) => {

+ tracing::debug!(

+ "found '{}' scanning '{path}' but it only has a confidence score of {}",

+ ided.id.name,

+ ided.confidence,

+ );

+ None

+ }

+ ScanResult::NoLicense => None,

+ }

+}

+

+struct Identified {

+ confidence: f32,

+ id: spdx::LicenseId,

+}

+

+enum ScanResult {

+ Header(Identified),

+ Text(Identified),

+ UnknownId(String),

+ LowLicenseChance(Identified),

+ NoLicense,

+}

+

+fn scan_text(contents: &str, strat: &sd::scan::Scanner<'_>, threshold: f32) -> ScanResult {

+ let text = spdx::detection::TextData::new(contents);

+ let lic_match = strat.scan(&text);

+

+ let Some(identified) = lic_match.license else {

+ return ScanResult::NoLicense;

+ };

+

+ let lic_id = match spdx::license_id(identified.name) {

+ Some(id) => Identified {

+ confidence: lic_match.score,

+ id,

+ },

+ None => return ScanResult::UnknownId(identified.name.to_owned()),

+ };

+

+ use spdx::detection::LicenseType;

+

+ if lic_match.score >= threshold {

+ match identified.kind {

+ LicenseType::Header => ScanResult::Header(lic_id),

+ LicenseType::Original => ScanResult::Text(lic_id),

+ LicenseType::Alternate => {

+ panic!("Alternate license detected")

+ }

+ }

+ } else {

+ ScanResult::LowLicenseChance(lic_id)

+ }

+}

+

+fn gather_licenses<'k>(krates: &'k Krates, store: &LicenseStore) -> Vec<KrateLicense<'k>> {

+ use rayon::prelude::*;

+

+ let min_threshold = (CONFIDENCE_THRESHOLD - 0.5).max(0.1);

+

+ let scanner = sd::scan::Scanner::new(store)

+ .confidence_threshold(min_threshold)

+ .optimize(false)

+ .max_passes(1);

+

+ let mut licensed_krates: Vec<_> = krates

+ .krates()

+ .par_bridge()

+ .filter_map(|krate| {

+ // Skip private/workspace crates

+ if IGNORE_PRIVATE

+ && let Some(publish) = &krate.publish

+ && publish.is_empty()

+ {

+ tracing::debug!("ignoring private crate '{krate}'");

+ return None;

+ }

+

+ let lic_info = krate.get_license_expression();

+ let root_path = krate.manifest_path.parent().unwrap();

+

+ let mut license_files = scan_files(root_path, &scanner, CONFIDENCE_THRESHOLD);

+

+ // Condense each license down to the best candidate if

+ // multiple are found

+ license_files.sort();

+ let mut last_expr = None;

+ license_files.retain(|lf| {

+ let dominated = last_expr.as_ref() == Some(&lf.license_expr);

+ last_expr = Some(lf.license_expr.clone());

+ !dominated

+ });

+

+ Some(KrateLicense {

+ krate,

+ lic_info,

+ license_files,

+ })

+ })

+ .collect();

+

+ licensed_krates.sort_by(|a, b| a.krate.cmp(b.krate));

+ licensed_krates

+}

+

+/// For an OR expression like "MIT OR Apache-2.0", pick the minimal set of

+/// licenses to satisfy the expression. Actual license policy validation

+/// is handled by `cargo deny`.

+fn pick_licenses(expr: &Expression) -> Vec<LicenseReq> {

+ let accepted: Vec<Licensee> = expr

+ .requirements()

+ .filter_map(|r| {

+ r.req

+ .license

+ .id()

+ .map(|id| Licensee::parse(id.name).unwrap())

+ })

+ .collect();

+

+ expr.minimized_requirements(&accepted).unwrap_or_default()

+}

+

+/// For crates without a `license` field, synthesize requirements from

+/// scanned license files.

+fn synthesize_from_files(files: &[LicenseFile]) -> Vec<LicenseReq> {

+ let mut reqs = Vec::new();

+ for lf in files {

+ for req in lf.license_expr.requirements() {

+ if !reqs.contains(&req.req) {

+ reqs.push(req.req.clone());

+ }

+ }

+ }

+ reqs

+}

+

+fn effective_licenses(kl: &KrateLicense<'_>) -> Vec<LicenseReq> {

+ match &kl.lic_info {

+ LicenseInfo::Expr(expr) => pick_licenses(expr),

+ LicenseInfo::Unknown => {

+ if kl.license_files.is_empty() {

+ tracing::warn!(

+ "unable to determine license for '{}': no `license` specified, and no license files were found",

+ kl.krate

+ );

+ Vec::new()

+ } else {

+ synthesize_from_files(&kl.license_files)

+ }

+ }

+ }

+}

+

+#[derive(Clone, Serialize)]

+struct UsedBy {

+ #[serde(rename = "crate")]

+ krate: UsedByCrate,

+}

+

+#[derive(Clone, Serialize)]

+struct UsedByCrate {

+ name: String,

+ version: String,

+ repository: Option<String>,

+}

+

+#[derive(Clone, Serialize)]

+struct License {

+ name: String,

+ id: String,

+ first_of_kind: bool,

+ text: String,

+ used_by: Vec<UsedBy>,

+}

+

+#[derive(Serialize)]

+struct LicenseSet {

+ count: usize,

+ name: String,

+ id: String,

+}

+

+#[derive(Serialize)]

+struct LicenseList {

+ overview: Vec<LicenseSet>,

+ licenses: Vec<License>,

+}

+

+fn generate(nfos: &[KrateLicense<'_>]) -> LicenseList {

+ let mut licenses_map: BTreeMap<String, BTreeMap<String, License>> = BTreeMap::new();

+

+ for krate_license in nfos {

+ let reqs = effective_licenses(krate_license);

+

+ for license_req in &reqs {

+ let spdx::LicenseItem::Spdx { id, .. } = license_req.license else {

+ tracing::warn!(

+ "{license_req} has no license file for crate '{}'",

+ krate_license.krate

+ );

+ continue;

+ };

+

+ // Try to find actual license text from scanned files

+ let license_text = krate_license

+ .license_files

+ .iter()

+ .find_map(|lf| {

+ if !lf

+ .license_expr

+ .evaluate(|ereq| ereq.license.id() == Some(id))

+ {

+ return None;

+ }

+

+ match &lf.kind {

+ LicenseFileKind::Text(text) => Some(text.clone()),

+ LicenseFileKind::Header => None,

+ }

+ })

+ .unwrap_or_else(|| {

+ tracing::debug!(

+ "unable to find text for license '{license_req}' for crate '{}', falling back to canonical text",

+ krate_license.krate

+ );

+ id.text().to_owned()

+ });

+

+ let used_by = UsedBy {

+ krate: UsedByCrate {

+ name: krate_license.krate.name.clone(),

+ version: krate_license.krate.version.to_string(),

+ repository: krate_license.krate.repository.clone(),

+ },

+ };

+

+ let entry = licenses_map.entry(id.full_name.to_owned()).or_default();

+

+ let lic = entry

+ .entry(license_text.clone())

+ .or_insert_with(|| License {

+ name: id.full_name.to_owned(),

+ id: id.name.to_owned(),

+ text: license_text,

+ used_by: Vec::new(),

+ first_of_kind: false,

+ });

+ lic.used_by.push(used_by);

+ }

+ }

+

+ let mut licenses: Vec<_> = licenses_map

+ .into_values()

+ .flat_map(|v| v.into_values())

+ .collect();

+

+ for lic in &mut licenses {

+ lic.used_by.sort_by_key(|used| used.krate.name.len());

+ }

+

+ licenses.sort_by(|a, b| a.id.cmp(&b.id));

+

+ let mut overview_map: BTreeMap<&str, LicenseSet> = BTreeMap::new();

+

+ for lic in &mut licenses {

+ let ls = overview_map.entry(&lic.id).or_insert_with(|| {

+ lic.first_of_kind = true;

+ LicenseSet {

+ count: 0,

+ name: lic.name.clone(),

+ id: lic.id.clone(),

+ }

+ });

+ ls.count += lic.used_by.len();

+ }

+

+ let mut overview: Vec<_> = overview_map.into_values().collect();

+ overview.sort_by(|a, b| a.name.cmp(&b.name));

+

+ LicenseList { overview, licenses }

+}

+

+/// Gathers all dependency licenses and returns a JSON string.

+pub fn generate_json(manifest_path: &str) -> Result<String, Box<dyn std::error::Error>> {

+ let manifest_path = Utf8PathBuf::from(manifest_path);

+ if !manifest_path.exists() {

+ return Err(format!("manifest path '{manifest_path}' does not exist").into());

+ }

+

+ let krates = get_all_crates(&manifest_path)?;

+ let store = load_license_store()?;

+ let summary = gather_licenses(&krates, &store);

+ let list = generate(&summary);

+

+ Ok(serde_json::to_string_pretty(&list)?)

+}