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// Copyright 2019 Google LLC.
// SPDX-License-Identifier: Apache-2.0
// This tool analyses external (i.e. not built with `buildGo.nix`) Go
// packages to determine a build plan that Nix can import.
package main
import (
"encoding/json"
"flag"
"fmt"
"go/build"
"log"
"os"
"path"
"path/filepath"
"strings"
)
// Path to a JSON file describing all standard library import paths.
// This file is generated and set here by Nix during the build
// process.
var stdlibList string
// pkg describes a single Go package within the specified source
// directory.
//
// Return information includes the local (relative from project root)
// and external (none-stdlib) dependencies of this package.
type pkg struct {
Name string `json:"name"`
Locator []string `json:"locator"`
Files []string `json:"files"`
SFiles []string `json:"sfiles"`
LocalDeps [][]string `json:"localDeps"`
ForeignDeps []foreignDep `json:"foreignDeps"`
IsCommand bool `json:"isCommand"`
}
type foreignDep struct {
Path string `json:"path"`
// filename, column and line number of the import, if known
Position string `json:"position"`
}
// findGoDirs returns a filepath.WalkFunc that identifies all
// directories that contain Go source code in a certain tree.
func findGoDirs(at string) ([]string, error) {
dirSet := make(map[string]bool)
err := filepath.Walk(at, func(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
name := info.Name()
// Skip folders that are guaranteed to not be relevant
if info.IsDir() && (name == "testdata" || name == ".git") {
return filepath.SkipDir
}
// If the current file is a Go file, then the directory is popped
// (i.e. marked as a Go directory).
if !info.IsDir() && strings.HasSuffix(name, ".go") && !strings.HasSuffix(name, "_test.go") {
dirSet[filepath.Dir(path)] = true
}
return nil
})
if err != nil {
return nil, err
}
goDirs := []string{}
for goDir := range dirSet {
goDirs = append(goDirs, goDir)
}
return goDirs, nil
}
// analysePackage loads and analyses the imports of a single Go
// package, returning the data that is required by the Nix code to
// generate a derivation for this package.
func analysePackage(root, source, importpath string, stdlib map[string]bool) (pkg, error) {
ctx := build.Default
ctx.CgoEnabled = false
p, err := ctx.ImportDir(source, build.IgnoreVendor)
if err != nil {
return pkg{}, err
}
local := [][]string{}
foreign := []foreignDep{}
for _, i := range p.Imports {
if stdlib[i] {
continue
}
if i == importpath {
local = append(local, []string{})
} else if strings.HasPrefix(i, importpath+"/") {
local = append(local, strings.Split(strings.TrimPrefix(i, importpath+"/"), "/"))
} else {
// The import positions is a map keyed on the import name.
// The value is a list, presumably because an import can appear
// multiple times in a package. Let’s just take the first one,
// should be enough for a good error message.
firstPos := p.ImportPos[i][0].String()
foreign = append(foreign, foreignDep{Path: i, Position: firstPos})
}
}
prefix := strings.TrimPrefix(source, root+"/")
locator := []string{}
if len(prefix) != len(source) {
locator = strings.Split(prefix, "/")
} else {
// Otherwise, the locator is empty since its the root package and
// no prefix should be added to files.
prefix = ""
}
files := []string{}
for _, f := range p.GoFiles {
files = append(files, path.Join(prefix, f))
}
sfiles := []string{}
for _, f := range p.SFiles {
sfiles = append(sfiles, path.Join(prefix, f))
}
return pkg{
Name: path.Join(importpath, prefix),
Locator: locator,
Files: files,
SFiles: sfiles,
LocalDeps: local,
ForeignDeps: foreign,
IsCommand: p.IsCommand(),
}, nil
}
func loadStdlibPkgs(from string) (pkgs map[string]bool, err error) {
f, err := os.ReadFile(from)
if err != nil {
return
}
err = json.Unmarshal(f, &pkgs)
return
}
func main() {
source := flag.String("source", "", "path to directory with sources to process")
path := flag.String("path", "", "import path for the package")
flag.Parse()
if *source == "" {
log.Fatalf("-source flag must be specified")
}
stdlibPkgs, err := loadStdlibPkgs(stdlibList)
if err != nil {
log.Fatalf("failed to load standard library index from %q: %s\n", stdlibList, err)
}
goDirs, err := findGoDirs(*source)
if err != nil {
log.Fatalf("failed to walk source directory '%s': %s", *source, err)
}
all := []pkg{}
for _, d := range goDirs {
analysed, err := analysePackage(*source, d, *path, stdlibPkgs)
// If the Go source analysis returned "no buildable Go files",
// that directory should be skipped.
//
// This might be due to `+build` flags on the platform and other
// reasons (such as test files).
if _, ok := err.(*build.NoGoError); ok {
continue
}
if err != nil {
log.Fatalf("failed to analyse package at %q: %s", d, err)
}
all = append(all, analysed)
}
j, _ := json.Marshal(all)
fmt.Println(string(j))
}
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