automatically detect Go module path

This started as a proof-of-concept for #30.

Signed-off-by: Dominik Menke <dom@digineo.de>

cmd/gci/gcicommand.go

@@ -30,6 +30,9 @@ func (e *Executor) newGciCommand(use, short, long string, aliases []string, stdI
 			if err != nil {
 				return err
 			}
+			if err = gciCfg.InitializeModules(args); err != nil {
+				return err
+			}
 			if *debug {
 				log.SetLevel(zapcore.DebugLevel)
 			}

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/spf13/cobra v1.3.0
 	github.com/stretchr/testify v1.7.0
 	go.uber.org/zap v1.17.0
+	golang.org/x/mod v0.5.0
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
 	golang.org/x/tools v0.1.5
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b
@@ -19,7 +20,6 @@ require (
 	github.com/spf13/pflag v1.0.5 // indirect
 	go.uber.org/atomic v1.7.0 // indirect
 	go.uber.org/multierr v1.6.0 // indirect
-	golang.org/x/mod v0.5.0 // indirect
 	golang.org/x/sys v0.0.0-20211216021012-1d35b9e2eb4e // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 )

pkg/gci/configuration.go

@@ -40,6 +40,45 @@ func (g GciStringConfiguration) Parse() (*GciConfiguration, error) {
 	return &GciConfiguration{g.Cfg, sections, sectionSeparators}, nil
 }
 
+// InitializeModules collects and remembers Go module names for the given
+// files, by traversing the file system.
+//
+// This method requires that g.Sections contains the Module section,
+// otherwise InitializeModules does nothing. This also implies that
+// this method should be called after changes to g.Sections, for example
+// right after (*GciStringConfiguration).Parse().
+func (g *GciConfiguration) InitializeModules(files []string) error {
+	var moduleSection *sectionsPkg.Module
+	for _, section := range g.Sections {
+		if m, ok := section.(sectionsPkg.Module); ok {
+			moduleSection = &m
+			break
+		}
+	}
+	if moduleSection == nil {
+		// skip collecting Go modules when not needed
+		return nil
+	}
+
+	resolver := make(moduleResolver)
+	knownModulePaths := map[string]struct{}{} // unique list of Go modules
+	for _, file := range files {
+		path, err := resolver.Lookup(file)
+		if err != nil {
+			return err
+		}
+		if path != "" {
+			knownModulePaths[path] = struct{}{}
+		}
+	}
+	modulePaths := make([]string, 0, len(knownModulePaths))
+	for path := range knownModulePaths {
+		modulePaths = append(modulePaths, path)
+	}
+	moduleSection.SetModulePaths(modulePaths)
+	return nil
+}
+
 func initializeGciConfigFromYAML(filePath string) (*GciConfiguration, error) {
 	yamlCfg := GciStringConfiguration{}
 	yamlData, err := ioutil.ReadFile(filePath)

pkg/gci/gci.go

@@ -28,7 +28,11 @@ func (list SectionList) String() []string {
 }
 
 func DefaultSections() SectionList {
-	return SectionList{sectionsPkg.StandardPackage{}, sectionsPkg.DefaultSection{nil, nil}}
+	return SectionList{
+		sectionsPkg.StandardPackage{},
+		sectionsPkg.DefaultSection{nil, nil},
+		sectionsPkg.Module{},
+	}
 }
 
 func DefaultSectionSeparators() SectionList {

pkg/gci/gci_test.go

@@ -39,6 +39,9 @@ func TestRun(t *testing.T) {
 			if err != nil {
 				t.Fatal(err)
 			}
+			if err = gciCfg.InitializeModules([]string{testFile}); err != nil {
+				t.Fatal(err)
+			}
 
 			_, formattedFile, err := LoadFormatGoFile(io.File{fileBaseName + ".in.go"}, *gciCfg)
 			if err != nil {

pkg/gci/internal/testdata/modules.cfg.yaml

@@ -0,0 +1,4 @@
+sections:
+- Standard
+- Module
+- Default

pkg/gci/internal/testdata/modules.in.go

@@ -0,0 +1,8 @@
+package main
+import (
+  "github.com/daixiang0/gci"
+
+  "golang.org/x/tools"
+
+  "fmt"
+)

pkg/gci/internal/testdata/modules.out.go

@@ -0,0 +1,8 @@
+package main
+import (
+	"fmt"
+
+	"github.com/daixiang0/gci"
+
+	"golang.org/x/tools"
+)

pkg/gci/mod.go

@@ -0,0 +1,100 @@
+package gci
+
+import (
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/mod/modfile"
+)
+
+// moduleResolver looksup the module path for a given (Go) file.
+// To improve performance, the file paths and module paths are
+// cached.
+//
+// Given the following directory structure:
+//
+//	/path/to/example
+//	+-- go.mod               (module example)
+//	+-- cmd/sample/main.go   (package main, imports example/util)
+//	+-- util/util.go         (package util)
+//
+// After looking up main.go and util.go, the internal cache will contain:
+//
+//	"/path/to/foobar/": "example"
+//
+// For more complex module structures (i.e. sub-modules), the cache
+// might look like this:
+//
+//	"/path/to/example/":            "example"
+//	"/path/to/example/cmd/sample/": "go.example.com/historic/path"
+//
+// When matching files against this cache, the resolver will select the
+// entry with the most specific path (so that, in this example, the file
+// cmd/sample/main.go will resolve to go.example.com/historic/path).
+type moduleResolver map[string]string
+
+func (m moduleResolver) Lookup(file string) (string, error) {
+	abs, err := filepath.Abs(file)
+	if err != nil {
+		return "", fmt.Errorf("could not make path absolute: %w", err)
+	}
+
+	var bestMatch string
+	for path := range m {
+		if strings.HasPrefix(abs, path) && len(path) > len(bestMatch) {
+			bestMatch = path
+		}
+	}
+	if bestMatch != "" {
+		return m[bestMatch], nil
+	}
+
+	return m.findRecursively(filepath.Dir(abs))
+}
+
+func (m moduleResolver) findRecursively(dir string) (string, error) {
+	// When going up the directory tree, we might never find a go.mod
+	// file. In this case remember where we started, so that the next
+	// time we can short circuit the recursive ascent.
+	stop := dir
+
+	for {
+		gomod := filepath.Join(dir, "go.mod")
+		_, err := os.Stat(gomod)
+		if errors.Is(err, os.ErrNotExist) {
+			// go.mod doesn't exist at current location
+			next := filepath.Dir(dir)
+			if next == dir {
+				// we're at the top of the filesystem
+				m[stop] = ""
+				return "", nil
+			}
+			// go one level up
+			dir = next
+			continue
+		} else if err != nil {
+			// other error (likely EPERM)
+			return "", fmt.Errorf("module lookup failed: %w", err)
+		}
+
+		// we found a go.mod
+		mod, err := ioutil.ReadFile(gomod)
+		if err != nil {
+			return "", fmt.Errorf("reading module failed: %w", err)
+		}
+
+		// store module path at m[dir]. add path separator to avoid
+		// false-positive (think of /foo and /foobar).
+		mpath := modfile.ModulePath(mod)
+		if dir != "/" {
+			// add trailing path sep, but not for *nix root directory
+			dir += string(os.PathListSeparator)
+		}
+		m[dir] = mpath
+		return mpath, nil
+	}
+}

pkg/gci/sections/module.go

@@ -0,0 +1,60 @@
+package sections
+
+import (
+	"strings"
+
+	"github.com/daixiang0/gci/pkg/configuration"
+	importPkg "github.com/daixiang0/gci/pkg/gci/imports"
+	"github.com/daixiang0/gci/pkg/gci/specificity"
+)
+
+func init() {
+	prefixType := SectionType{
+		generatorFun: func(parameter string, sectionPrefix, sectionSuffix Section) (Section, error) {
+			return Module{}, nil
+		},
+		aliases:     []string{"Module", "Mod"},
+		description: "Groups all imports of the corresponding Go module",
+	}.StandAloneSection().WithoutParameter()
+	SectionParserInst.registerSectionWithoutErr(&prefixType)
+}
+
+type Module struct {
+	// modulePaths contains all known Go module path names.
+	//
+	// This must be a pointer, because gci.formatImportBlock() will create
+	// mapping between sections and imports, and slices are unhashable.
+	modulePaths *[]string
+}
+
+func (m Module) MatchSpecificity(spec importPkg.ImportDef) specificity.MatchSpecificity {
+	if m.modulePaths == nil {
+		return specificity.MisMatch{}
+	}
+
+	importPath := spec.Path()
+	for _, path := range *m.modulePaths {
+		if strings.HasPrefix(importPath, path) {
+			return specificity.Module{}
+		}
+	}
+	return specificity.MisMatch{}
+}
+
+func (m Module) Format(imports []importPkg.ImportDef, cfg configuration.FormatterConfiguration) string {
+	return inorderSectionFormat(m, imports, cfg)
+}
+
+func (Module) sectionPrefix() Section { return nil }
+func (Module) sectionSuffix() Section { return nil }
+
+func (Module) String() string {
+	return "Module"
+}
+
+func (m *Module) SetModulePaths(paths []string) {
+	dup := make([]string, len(paths), len(paths))
+	copy(dup, paths)
+
+	m.modulePaths = &dup
+}

pkg/gci/specificity/module.go

@@ -0,0 +1,19 @@
+package specificity
+
+type Module struct{}
+
+func (m Module) IsMoreSpecific(than MatchSpecificity) bool {
+	return isMoreSpecific(m, than)
+}
+
+func (m Module) Equal(to MatchSpecificity) bool {
+	return equalSpecificity(m, to)
+}
+
+func (Module) class() specificityClass {
+	return ModuleClass
+}
+
+func (Module) String() string {
+	return "Module"
+}

pkg/gci/specificity/specificity.go

@@ -7,6 +7,7 @@ const (
 	DefaultClass         = 10
 	StandardPackageClass = 20
 	MatchClass           = 30
+	ModuleClass          = 40
 )
 
 // MatchSpecificity is used to determine which section matches an import best

pkg/gci/specificity/specificity_test.go

@@ -25,5 +25,5 @@ func TestSpecificityEquality(t *testing.T) {
 }
 
 func testCasesInSpecificityOrder() []MatchSpecificity {
-	return []MatchSpecificity{MisMatch{}, Default{}, StandardPackageMatch{}, Match{0}, Match{1}}
+	return []MatchSpecificity{MisMatch{}, Default{}, StandardPackageMatch{}, Match{0}, Match{1}, Module{}}
 }