github.com/anchore/syft@v1.38.2/internal/spdxlicense/generate/generate_license_list.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"regexp"
	"sort"
	"strings"
	"text/template"
)

// This program generates license_list.go.
const (
	source = "license_list.go"
	url    = "https://spdx.org/licenses/licenses.json"
)

var tmp = template.Must(template.New("").Parse(`// Code generated by go generate; DO NOT EDIT.
// This file was generated using data from {{ .URL }}
package spdxlicense

const Version = {{ printf "%q" .Version }}

var licenseIDs = map[string]string{
{{- range $k, $v := .LicenseIDs }}
	{{ printf "%q" $k }}: {{ printf "%q" $v }},
{{- end }}
}

// urlToLicense maps license URLs from the seeAlso field to license IDs
var urlToLicense = map[string]string{
{{- range $url, $id := .URLToLicense }}
	{{ printf "%q" $url }}: {{ printf "%q" $id }},
{{- end }}
}
`))

var versionMatch = regexp.MustCompile(`([0-9]+)\.?([0-9]+)?\.?([0-9]+)?\.?`)

func main() {
	if err := run(); err != nil {
		fmt.Println(err.Error())
		os.Exit(1)
	}
}

func run() error {
	resp, err := http.Get(url)
	if err != nil {
		return fmt.Errorf("unable to get licenses list: %w", err)
	}
	var result LicenseList
	if err = json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return fmt.Errorf("unable to decode license list: %w", err)
	}
	defer func() {
		if err := resp.Body.Close(); err != nil {
			log.Fatalf("unable to close body: %+v", err)
		}
	}()

	f, err := os.Create(source)
	if err != nil {
		return fmt.Errorf("unable to create %q: %w", source, err)
	}
	defer func() {
		if err := f.Close(); err != nil {
			log.Fatalf("unable to close %q: %+v", source, err)
		}
	}()

	licenseIDs := processSPDXLicense(result)
	urlToLicense := buildURLToLicenseMap(result)

	err = tmp.Execute(f, struct {
		URL          string
		Version      string
		LicenseIDs   map[string]string
		URLToLicense map[string]string
	}{
		URL:          url,
		Version:      result.Version,
		LicenseIDs:   licenseIDs,
		URLToLicense: urlToLicense,
	})

	if err != nil {
		return fmt.Errorf("unable to generate template: %w", err)
	}
	return nil
}

// Parsing the provided SPDX license list necessitates a three pass approach.
// The first pass is only related to what SPDX considers the truth. We use license info to
// find replacements for deprecated licenses.
// The second pass attempts to generate known short/long version listings for each key.
// For info on some short name conventions see this document:
// https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/#license-short-name.
// The short long listing generation attempts to build all license permutations for a given key.
// The new keys are then also associated with their relative SPDX value. If a key has already been entered
// we know to ignore it since it came from the first pass which is considered the SPDX source of truth.
// We also sort the licenses for the second pass so that cases like `GPL-1` associate to `GPL-1.0` and not `GPL-1.1`.
// The third pass is for overwriting deprecated licenses with replacements, for example GPL-2.0+ is deprecated
// and now maps to GPL-2.0-or-later.
func processSPDXLicense(result LicenseList) map[string]string {
	// The order of variations/permutations of a license ID matter.
	// The permutation code can generate the same value for two difference licenses,
	// for example: The licenses `ABC-1.0` and `ABC-1.1` can both map to `ABC1`,
	// we need to guarantee the order they are created to avoid mapping them incorrectly.
	// To do this we use a sorted list.
	sort.Slice(result.Licenses, func(i, j int) bool {
		return result.Licenses[i].ID < result.Licenses[j].ID
	})

	// keys are simplified by removing dashes and lowercasing ID
	// this is so license declarations in the wild like: LGPL3 LGPL-3 lgpl3 and lgpl-3 can all match
	licenseIDs := make(map[string]string)
	for _, l := range result.Licenses {
		// licensePerms includes the cleanID in return slice
		cleanID := cleanLicenseID(l.ID)
		licensePerms := buildLicenseIDPermutations(cleanID)

		// if license is deprecated, find its replacement and add to licenseIDs
		if l.Deprecated {
			idToMap := l.ID
			replacement := result.findReplacementLicense(l)
			if replacement != nil {
				idToMap = replacement.ID
			}
			// it's important to use the original licensePerms here so that the deprecated license
			// can now point to the new correct license
			for _, id := range licensePerms {
				if _, exists := licenseIDs[id]; exists {
					// can be used to debug duplicate license permutations and confirm that examples like GPL1
					// do not point to GPL-1.1
					// log.Println("duplicate license list permutation found when mapping deprecated license to replacement")
					// log.Printf("already have key: %q for SPDX ID: %q; attempted to map replacement ID: %q for deprecated ID: %q\n", id, value, replacement.ID, l.ID)
					continue
				}
				licenseIDs[id] = idToMap
			}
		}

		// if license is not deprecated, add all permutations to licenseIDs
		for _, id := range licensePerms {
			if _, exists := licenseIDs[id]; exists {
				// log.Println("found duplicate license permutation key for non deprecated license")
				// log.Printf("already have key: %q for SPDX ID: %q; tried to insert as SPDX ID:%q\n", id, value, l.ID)
				continue
			}
			licenseIDs[id] = l.ID
		}
	}

	return licenseIDs
}

func cleanLicenseID(id string) string {
	cleanID := strings.ToLower(id)
	return strings.ReplaceAll(cleanID, "-", "")
}

// buildURLToLicenseMap creates a mapping from license URLs (from seeAlso fields) to license IDs
func buildURLToLicenseMap(result LicenseList) map[string]string {
	urlMap := make(map[string]string)

	for _, l := range result.Licenses {
		// Skip deprecated licenses
		if l.Deprecated {
			// Find replacement license if available
			replacement := result.findReplacementLicense(l)
			if replacement != nil {
				// Map deprecated license URLs to the replacement license
				for _, url := range l.SeeAlso {
					urlMap[url] = replacement.ID
				}
			}
			continue
		}

		// Add URLs from non-deprecated licenses
		for _, url := range l.SeeAlso {
			urlMap[url] = l.ID
		}
	}

	return urlMap
}