Add basic attempt at local module handling

The idea here is to support a new formatting section, `module`, which is
the module we're currently running in as a replacement for
`prefix(module/we/are/running/in)`.

Since this is dependent on the directory structure and where things are
run, some tests have been added which run on a real module structure.

This approach just focusses on the use-case of running `gci` from
the top level of a module. It does not, for example support:

* Discovering modules with a nested structure
* Discovering modules defined in a `go.work` file

It was considered to get the module from `go list -m`, but this would
drag in all modules defined under the current directory (i.e. those in
`go.work`) which might be confusing if those modules are importing each
other. This could be improved, if we know the name of the file whose
imports we're processing we could check if that file is under the
directory of a given local module (possible improvement for the future).

Another alternative to consider would be using query patterns with
`golang.org/x/tools/go/packages` e.g.

    config := packages.Config{Mode: packages.NeedModule | packages.NeedFiles | packages.NeedName}
    // where each "file=" maps to a file given as an argument to gci
    packages, err := packages.Load(
        &config,
        "file=./path/to/file.go",
        "file=./path/to/other.go",
    )

Signed-off-by: Matthew Hughes <matthewhughes934@gmail.com>

README.md

@@ -27,16 +27,17 @@ import (
 )
 ```
 
-GCI splits all import blocks into different sections, now support five section type:
+GCI splits all import blocks into different sections, now support six section type:
 
 - standard: Go official imports, like "fmt"
 - custom: Custom section, use full and the longest match (match full string first, if multiple matches, use the longest one)
 - default: All rest import blocks
 - blank: Put blank imports together in a separate group
 - dot: Put dot imports together in a separate group
 - alias: Put alias imports together in a separate group
+- localmodule: Put imports from local packages in a separate group
 
-The priority is standard > default > custom > blank > dot > alias, all sections sort alphabetically inside.
+The priority is standard > default > custom > blank > dot > alias > localmodule, all sections sort alphabetically inside.
 By default, blank , dot and alias sections are not used and the corresponding lines end up in the other groups.
 
 All import blocks use one TAB(`\t`) as Indent.
@@ -47,6 +48,17 @@ Since v0.9.0, GCI always puts C import block as the first.
 
 `nolint` is hard to handle at section level, GCI will consider it as a single comment.
 
+### LocalModule
+
+Local module detection is done via listing packages from *the directory where
+`gci` is invoked* and reading the modules off these. This means:
+
+  - This mode works when `gci` is invoked from a module root (i.e. directory
+    containing `go.mod`)
+  - This mode doesn't work with a multi-module setup, i.e. when `gci` is invoked
+    from a directory containing `go.work` (though it would work if invoked from
+    within one of the modules in the workspace)
+
 ## Installation
 
 To download and install the highest available release version -
@@ -321,6 +333,32 @@ import (
 )
 ```
 
+### with localmodule grouping enabled
+
+Assuming this is run on the root of this repo (i.e. where
+`github.com/daixiang0/gci` is a local module)
+
+```go
+package main
+
+import (
+	"os"
+	"github.com/daixiang0/gci/cmd/gci"
+)
+```
+
+to
+
+```go
+package main
+
+import (
+	"os"
+
+	"github.com/daixiang0/gci/cmd/gci"
+)
+```
+
 ## TODO
 
 - Ensure only one blank between `Name` and `Path` in an import block

pkg/config/config.go

@@ -10,12 +10,13 @@ import (
 )
 
 var defaultOrder = map[string]int{
-	section.StandardType: 0,
-	section.DefaultType:  1,
-	section.CustomType:   2,
-	section.BlankType:    3,
-	section.DotType:      4,
-	section.AliasType:    5,
+	section.StandardType:    0,
+	section.DefaultType:     1,
+	section.CustomType:      2,
+	section.BlankType:       3,
+	section.DotType:         4,
+	section.AliasType:       5,
+	section.LocalModuleType: 6,
 }
 
 type BoolConfig struct {
@@ -49,6 +50,9 @@ func (g YamlConfig) Parse() (*Config, error) {
 	if sections == nil {
 		sections = section.DefaultSections()
 	}
+	if err := configureSections(sections); err != nil {
+		return nil, err
+	}
 
 	// if default order sorted sections
 	if !g.Cfg.CustomOrder {
@@ -88,3 +92,15 @@ func ParseConfig(in string) (*Config, error) {
 
 	return gciCfg, nil
 }
+
+func configureSections(sections section.SectionList) error {
+	for _, sec := range sections {
+		switch s := sec.(type) {
+		case *section.LocalModule:
+			if err := s.Configure(); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}

pkg/gci/gci_test.go

@@ -2,11 +2,16 @@ package gci
 
 import (
 	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/daixiang0/gci/pkg/config"
+	"github.com/daixiang0/gci/pkg/io"
 	"github.com/daixiang0/gci/pkg/log"
 )
 
@@ -38,3 +43,71 @@ func TestRun(t *testing.T) {
 		})
 	}
 }
+
+func chdir(t *testing.T, dir string) {
+	oldWd, err := os.Getwd()
+	require.NoError(t, err)
+	require.NoError(t, os.Chdir(dir))
+
+	// change back at the end of the test
+	t.Cleanup(func() { os.Chdir(oldWd) })
+}
+
+func readConfig(t *testing.T, configPath string) *config.Config {
+	rawConfig, err := os.ReadFile(configPath)
+	require.NoError(t, err)
+	config, err := config.ParseConfig(string(rawConfig))
+	require.NoError(t, err)
+
+	return config
+}
+
+func TestRunWithLocalModule(t *testing.T) {
+	moduleDir := filepath.Join("testdata", "module")
+	// files with a corresponding '*.out.go' file containing the expected
+	// result of formatting
+	testedFiles := []string{
+		"main.go",
+		filepath.Join("internal", "foo", "lib.go"),
+	}
+
+	// run subtests for expected module loading behaviour
+	chdir(t, moduleDir)
+	cfg := readConfig(t, "config.yaml")
+
+	for _, path := range testedFiles {
+		t.Run(path, func(t *testing.T) {
+			// *.go -> *.out.go
+			expected, err := os.ReadFile(strings.TrimSuffix(path, ".go") + ".out.go")
+			require.NoError(t, err)
+
+			_, got, err := LoadFormatGoFile(io.File{path}, *cfg)
+
+			require.NoError(t, err)
+			require.Equal(t, string(expected), string(got))
+		})
+	}
+}
+
+func TestRunWithLocalModuleWithPackageLoadFailure(t *testing.T) {
+	// just a directory with no Go modules
+	dir := t.TempDir()
+	configContent := "sections:\n  - LocalModule\n"
+
+	chdir(t, dir)
+	_, err := config.ParseConfig(configContent)
+	require.ErrorContains(t, err, "failed to load local modules: ")
+}
+
+func TestRunWithLocalModuleWithModuleLookupError(t *testing.T) {
+	dir := t.TempDir()
+	// error from trying to list packages under module with no go files
+	configContent := "sections:\n  - LocalModule\n"
+	goModContent := "module example.com/foo\n"
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "go.mod"), []byte(goModContent), 0o644))
+
+	chdir(t, dir)
+	_, err := config.ParseConfig(configContent)
+	require.ErrorContains(t, err, "error reading local packages: ")
+	require.ErrorContains(t, err, dir)
+}

pkg/gci/testdata.go

@@ -1273,6 +1273,29 @@ import (
 	testing "github.com/daixiang0/test"
 	g "github.com/golang"
 )
+`,
+	},
+	{
+		"basic module",
+		// implicitly relies on the local module name being: github.com/daixiang0/gci
+		`sections:
+  - Standard
+  - LocalModule
+`,
+		`package main
+
+import (
+	"os"
+	"github.com/daixiang0/gci/cmd/gci"
+)
+`,
+		`package main
+
+import (
+	"os"
+
+	"github.com/daixiang0/gci/cmd/gci"
+)
 `,
 	},
 }

pkg/gci/testdata/module/.gitattributes

@@ -0,0 +1,4 @@
+# try and stop git running on Windows from converting line endings from
+# in all Go files under this directory. This is to avoid inconsistent test
+# results when `gci` strips "\r" characters
+**/*.go eol=lf

pkg/gci/testdata/module/config.yaml

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

pkg/gci/testdata/module/go.mod

@@ -0,0 +1,3 @@
+module example.com/simple
+
+go 1.20

pkg/gci/testdata/module/internal/bar/lib.go

@@ -0,0 +1 @@
+package bar

pkg/gci/testdata/module/internal/foo/lib.go

@@ -0,0 +1,6 @@
+package foo
+
+import (
+	"example.com/simple/internal/bar"
+	"log"
+)

pkg/gci/testdata/module/internal/foo/lib.out.go

@@ -0,0 +1,7 @@
+package foo
+
+import (
+	"log"
+
+	"example.com/simple/internal/bar"
+)

pkg/gci/testdata/module/internal/lib.go

@@ -0,0 +1 @@
+package internal

pkg/gci/testdata/module/main.go

@@ -0,0 +1,9 @@
+package lib
+
+import (
+	"golang.org/x/net"
+	"example.com/simple/internal"
+	"example.com/simple/internal/foo"
+	"example.com/simple/internal/bar"
+	"log"
+)

pkg/gci/testdata/module/main.out.go

@@ -0,0 +1,11 @@
+package lib
+
+import (
+	"log"
+
+	"golang.org/x/net"
+
+	"example.com/simple/internal"
+	"example.com/simple/internal/bar"
+	"example.com/simple/internal/foo"
+)

pkg/section/local_module.go

@@ -0,0 +1,77 @@
+package section
+
+import (
+	"fmt"
+	"strings"
+
+	"golang.org/x/tools/go/packages"
+
+	"github.com/daixiang0/gci/pkg/parse"
+	"github.com/daixiang0/gci/pkg/specificity"
+)
+
+const LocalModuleType = "localmodule"
+
+type LocalModule struct {
+	Paths []string
+}
+
+func (m *LocalModule) MatchSpecificity(spec *parse.GciImports) specificity.MatchSpecificity {
+	for _, modPath := range m.Paths {
+		// also check path etc.
+		if strings.HasPrefix(spec.Path, modPath) {
+			return specificity.LocalModule{}
+		}
+	}
+
+	return specificity.MisMatch{}
+}
+
+func (m *LocalModule) String() string {
+	return LocalModuleType
+}
+
+func (m *LocalModule) Type() string {
+	return LocalModuleType
+}
+
+// Configure configures the module section by finding the module
+// for the current path
+func (m *LocalModule) Configure() error {
+	modPaths, err := findLocalModules()
+	if err != nil {
+		return err
+	}
+	m.Paths = modPaths
+	return nil
+}
+
+func findLocalModules() ([]string, error) {
+	packages, err := packages.Load(
+		// find the package in the current dir and load its module
+		// NeedFiles so there is some more info in package errors
+		&packages.Config{Mode: packages.NeedModule | packages.NeedFiles},
+		".",
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load local modules: %v", err)
+	}
+
+	uniqueModules := make(map[string]struct{})
+
+	for _, pkg := range packages {
+		if len(pkg.Errors) != 0 {
+			return nil, fmt.Errorf("error reading local packages: %v", pkg.Errors)
+		}
+		if pkg.Module != nil {
+			uniqueModules[pkg.Module.Path] = struct{}{}
+		}
+	}
+
+	modPaths := make([]string, 0, len(uniqueModules))
+	for mod := range uniqueModules {
+		modPaths = append(modPaths, mod)
+	}
+
+	return modPaths, nil
+}

pkg/section/parser.go

@@ -35,6 +35,9 @@ func Parse(data []string) (SectionList, error) {
 			list = append(list, Blank{})
 		} else if s == "alias" {
 			list = append(list, Alias{})
+		} else if s == "localmodule" {
+			// pointer because we need to mutate the section at configuration time
+			list = append(list, &LocalModule{})
 		} else {
 			errString += fmt.Sprintf(" %s", s)
 		}

pkg/specificity/local_module.go

@@ -0,0 +1,15 @@
+package specificity
+
+type LocalModule struct{}
+
+func (m LocalModule) IsMoreSpecific(than MatchSpecificity) bool {
+	return isMoreSpecific(m, than)
+}
+
+func (m LocalModule) Equal(to MatchSpecificity) bool {
+	return equalSpecificity(m, to)
+}
+
+func (LocalModule) class() specificityClass {
+	return LocalModuleClass
+}