Fixes for puku init step & codelab

ChangeLog

@@ -4,6 +4,7 @@ Version 17.34.0
     * Check status field of fetch blob response (#3607)
     * Subinclude cycle detection (#3615)
     * Fix for `plz export --notrim` in some cases (#3621)
+    * `plz init plugin go` now writes a filegroup for `go.mod` and sets `modfile` (#3587)
 
 Version 17.33.0
 ---------------

docs/codelabs/puku.md

@@ -54,21 +54,14 @@ Define a valid Puku version number as a build configuration string in `.plzconfi
 
 ```
 [BuildConfig]
-puku-version = "1.17.0"
+puku-version = "1.17.1"
 ```
 
-Uncomment and edit the following lines in your `.plzconfig` to set up `please` version:
-
-```
-[please]
-version = 17.22.0
-```
-
-Configure a Please alias for Puku (optional but convenient):
+Configure a Please alias for Puku:
 
 ```
 [Alias "puku"]
-Cmd = run //third_party/binary:puku --
+Cmd = run --wd=. //third_party/binary:puku --
 PositionalLabels = true
 Desc = A tool to update BUILD files in Go packages
 ```
@@ -85,9 +78,10 @@ remote_file(
 )
 ```
 
-Configure the Go plugin to point at your go.mod (recommended). Create a repo-root `BUILD` with a filegroup for go.mod:
+Because you ran `plz init plugin go` in a directory that already had a `go.mod`, the Go plugin
+has been pointed at it for you. `plz init` will have written a filegroup exporting `go.mod` into
+your repo-root `BUILD` file:
 
-1) Add a filegroup for go.mod at `BUILD` in repo root:
 ```python
 filegroup(
     name = "gomod",
@@ -96,14 +90,16 @@ filegroup(
 )
 ```
 
-2) Update your `.plzconfig`:
+along with the corresponding `ModFile` setting in your `.plzconfig`:
+
 ```
 [Plugin "go"]
-Target = //plugins:go
 ModFile = //:gomod
 ```
 
 This lets Puku use standard `go get` to resolve modules, then sync them into `third_party/go/BUILD`.
+If you're adding Please to a repo that didn't have a `go.mod` at the time you ran `plz init plugin go`,
+you'll need to add those two pieces yourself.
 
 ### Configuring the PATH for Go
 
@@ -135,14 +131,6 @@ Path = /usr/local/go/bin:/usr/local/bin:/usr/bin:/bin
 
 **Note:** On Windows, use `where.exe go` to find the Go installation path.
 
-### Installing the Go standard library (Go 1.20+)
-
-From Go version 1.20 onwards, the standard library is no longer included by default with the Go distribution. You must install it manually:
-
-```bash
-GODEBUG="installgoroot=all" go install std
-```
-
 ## Adding and updating modules
 Duration: 5
 
@@ -172,14 +160,6 @@ Now add the dependency with `go get`:
 go get github.com/google/uuid
 ```
 
-Sync the changes to `third_party/go/BUILD`:
-
-```bash
-plz puku sync -w
-```
-
-This creates a `go_repo()` rule in `third_party/go/BUILD` for the `uuid` module. You may need to create the `third_party/go/BUILD` file if it doesn't exist.
-
 ### Creating the BUILD file
 
 Create `src/hello/BUILD`:
@@ -210,14 +190,14 @@ plz run //src/hello
 To update a module to a specific version:
 
 ```bash
-GOTOOLCHAIN=local go get github.com/google/uuid@v1.6.0
+go get github.com/google/uuid@v1.5.0
 plz puku sync -w
 ```
 
 To update to the latest version:
 
 ```bash
-GOTOOLCHAIN=local go get -u github.com/google/uuid
+go get -u github.com/google/uuid
 plz puku sync -w
 ```
 

src/plzinit/init_test.go

@@ -2,6 +2,7 @@ package plzinit
 
 import (
 	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -32,3 +33,54 @@ func TestInitPleasings(t *testing.T) {
 
 	assert.Equal(t, expectedRule, string(b))
 }
+
+const expectedGoModFilegroup = `filegroup(
+    name = "gomod",
+    srcs = ["go.mod"],
+    visibility = ["PUBLIC"],
+)
+`
+
+func TestInitGoMod(t *testing.T) {
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module example_module\n"), 0644))
+
+	label, err := initGoMod(dir)
+	require.NoError(t, err)
+	assert.Equal(t, "//:gomod", label)
+
+	b, err := os.ReadFile(filepath.Join(dir, "BUILD"))
+	require.NoError(t, err)
+	assert.Equal(t, expectedGoModFilegroup, string(b))
+}
+
+func TestInitGoModWithoutGoMod(t *testing.T) {
+	dir := t.TempDir()
+
+	label, err := initGoMod(dir)
+	require.NoError(t, err)
+	assert.Equal(t, "", label)
+	assert.False(t, fs.FileExists(filepath.Join(dir, "BUILD")))
+}
+
+func TestInitGoModReusesExistingFilegroup(t *testing.T) {
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module example_module\n"), 0644))
+
+	existing := `filegroup(
+    name = "modfile",
+    srcs = ["go.mod"],
+    visibility = ["PUBLIC"],
+)
+`
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "BUILD"), []byte(existing), 0644))
+
+	label, err := initGoMod(dir)
+	require.NoError(t, err)
+	assert.Equal(t, "//:modfile", label)
+
+	// The existing build file should be left alone.
+	b, err := os.ReadFile(filepath.Join(dir, "BUILD"))
+	require.NoError(t, err)
+	assert.Equal(t, existing, string(b))
+}

src/plzinit/plugin_go.go

@@ -5,15 +5,22 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"path/filepath"
 	"runtime"
+	"slices"
 	"strings"
 
 	"github.com/please-build/buildtools/build"
 
 	"github.com/thought-machine/please/src/fs"
 )
 
-const buildFilePath = "third_party/go/BUILD"
+const (
+	buildFilePath     = "third_party/go/BUILD"
+	rootBuildFileName = "BUILD"
+	goModFileName     = "go.mod"
+	goModFilegroup    = "gomod"
+)
 
 type goVersionResp = []struct {
 	Version string `json:"version"`
@@ -44,18 +51,18 @@ func getLatestGoVersion() (string, error) {
 	return runtime.Version(), nil
 }
 
-func parseBuildFile() (*build.File, error) {
-	bs, _ := os.ReadFile(buildFilePath)
-	return build.Parse(buildFilePath, bs)
+func parseBuildFile(path string) (*build.File, error) {
+	bs, _ := os.ReadFile(path)
+	return build.Parse(path, bs)
 }
 
-func saveFile(buildFile *build.File) error {
+func saveFile(buildFile *build.File, path string) error {
 	bs := build.Format(buildFile)
-	if err := fs.EnsureDir(buildFilePath); err != nil {
+	if err := fs.EnsureDir(path); err != nil {
 		return err
 	}
 
-	return os.WriteFile(buildFilePath, bs, 0666)
+	return os.WriteFile(path, bs, 0666)
 }
 
 func initGo() (map[string]string, error) {
@@ -69,7 +76,7 @@ func initGo() (map[string]string, error) {
 		return nil, err
 	}
 
-	buildFile, err := parseBuildFile()
+	buildFile, err := parseBuildFile(buildFilePath)
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse %s: %w", buildFilePath, err)
 	}
@@ -88,14 +95,63 @@ func initGo() (map[string]string, error) {
 		buildFile.Stmt = append(buildFile.Stmt, stdLib("std"))
 	}
 
-	if err := saveFile(buildFile); err != nil {
+	if err := saveFile(buildFile, buildFilePath); err != nil {
 		return nil, err
 	}
 
-	return map[string]string{
+	config := map[string]string{
 		"GoTool": toolchainRule,
 		"STDLib": stdRule,
-	}, nil
+	}
+
+	// Point the plugin at the repo's go.mod, if it has one. Without this, tools like puku
+	// can't reconcile the module requirements against the third party build file.
+	modFile, err := initGoMod(".")
+	if err != nil {
+		return nil, err
+	}
+	if modFile != "" {
+		config["ModFile"] = modFile
+	}
+
+	return config, nil
+}
+
+// initGoMod exports the repo's go.mod via a filegroup in the root build file, returning the
+// label of that filegroup. It returns an empty label if the repo doesn't have a go.mod.
+func initGoMod(dir string) (string, error) {
+	if _, ok := findGoModule(dir); !ok {
+		return "", nil
+	}
+
+	path := filepath.Join(dir, rootBuildFileName)
+	buildFile, err := parseBuildFile(path)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse %s: %w", path, err)
+	}
+
+	// Reuse an existing filegroup if the repo already exports go.mod under another name.
+	for _, rule := range buildFile.Rules("filegroup") {
+		if slices.Equal(rule.AttrStrings("srcs"), []string{goModFileName}) {
+			return "//:" + rule.Name(), nil
+		}
+	}
+
+	buildFile.Stmt = append(buildFile.Stmt, modFilegroup(goModFilegroup))
+	if err := saveFile(buildFile, path); err != nil {
+		return "", err
+	}
+
+	return "//:" + goModFilegroup, nil
+}
+
+func modFilegroup(name string) *build.CallExpr {
+	r := build.NewRule(&build.CallExpr{})
+	r.SetKind("filegroup")
+	r.SetAttr("name", &build.StringExpr{Value: name})
+	r.SetAttr("srcs", &build.ListExpr{List: []build.Expr{&build.StringExpr{Value: goModFileName}}})
+	r.SetAttr("visibility", &build.ListExpr{List: []build.Expr{&build.StringExpr{Value: "PUBLIC"}}})
+	return r.Call
 }
 
 func goToolchain(name, version string) *build.CallExpr {

test/plugins/BUILD

@@ -94,6 +94,18 @@ plugin_e2e_test(
     plz_command = "cp .plzconfig .foo; mv .foo .plzconfig; plz init plugin go && plz query config plugin.go.gotool > go.conf && plz query config plugin.go.stdlib >> go.conf",
 )
 
+# If the repo has a go.mod, init should export it and point the plugin at it, so that puku
+# has something to sync the third party build file against.
+plugin_e2e_test(
+    name = "init_go_modfile_test",
+    expect_output_contains = {
+        "go.conf": "//:gomod",
+        "BUILD": "filegroup*gomod*go.mod*PUBLIC",
+    },
+    # Need to break hard link here so init_plugin_test's actual .plzconfig doesn't get updated.
+    plz_command = "cp .plzconfig .foo; mv .foo .plzconfig; echo 'module example_module' > go.mod; plz init plugin go && plz query config plugin.go.modfile > go.conf",
+)
+
 # Test that the target is created in plugins/BUILD
 plugin_e2e_test(
     name = "init_create_target_test",