all: fix duplicate package docs and tighten TestPackageDocsmain

TestPackageDocs walked into directories starting with "." (such as
.claude worktrees) and only logged warnings on duplicate package docs
across files in a directory. Skip dot-directories (which covers the
old .git but also .claude), ignore files with "//go:build ignore" so
command files don't falsely trip the duplicate check, and promote the
duplicate-doc warning to a t.Errorf.

While here, deduplicate the package docs that were previously only
logged: drop the redundant comment from client/systray/startup-creator.go,
move the comprehensive taildrop doc into feature/taildrop/doc.go, and
remove a leftover doc fragment from feature/condlite/expvar/omit.go.

The tstest/integration/vms allowlist is no longer needed since the
//go:build ignore filter now handles its dns_tester.go and udp_tester.go
files generically.

Fixes #19526

Change-Id: Id794d96bd728826a1883a054e4a244f90fa05d3d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

1 files changed, 18 insertions, 9 deletions

diff --git a/pkgdoc_test.go b/pkgdoc_test.go
index 60b2d4856..c5e50ee63 100644
--- a/pkgdoc_test.go
+++ b/pkgdoc_test.go
@@ -4,6 +4,7 @@
 package tailscaleroot
 
 import (
+	"go/ast"
 	"go/parser"
 	"go/token"
 	"os"
@@ -13,6 +14,17 @@ import (
 	"testing"
 )
 
+func hasIgnoreBuildTag(f *ast.File) bool {
+	for _, cg := range f.Comments {
+		for _, c := range cg.List {
+			if c.Text == "//go:build ignore" {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 func TestPackageDocs(t *testing.T) {
 	switch runtime.GOOS {
 	case "darwin", "linux":
@@ -26,8 +38,8 @@ func TestPackageDocs(t *testing.T) {
 		if err != nil {
 			return err
 		}
-		if fi.Mode().IsDir() && path == ".git" {
-			return filepath.SkipDir // No documentation lives in .git
+		if fi.Mode().IsDir() && path != "." && strings.HasPrefix(filepath.Base(path), ".") {
+			return filepath.SkipDir // No documentation lives in dot directories (.git, .claude, etc)
 		}
 		if fi.Mode().IsRegular() && strings.HasSuffix(path, ".go") {
 			if strings.HasSuffix(path, "_test.go") {
@@ -48,6 +60,9 @@ func TestPackageDocs(t *testing.T) {
 		if err != nil {
 			t.Fatalf("failed to ParseFile %q: %v", fileName, err)
 		}
+		if hasIgnoreBuildTag(f) {
+			continue
+		}
 		dir := filepath.Dir(fileName)
 		if _, ok := byDir[dir]; !ok {
 			byDir[dir] = nil
@@ -61,14 +76,8 @@ func TestPackageDocs(t *testing.T) {
 		}
 	}
 	for dir, ff := range byDir {
-		switch dir {
-		case "tstest/integration/vms":
-			// This package has a couple go:build ignore commands and this test doesn't
-			// handle parsing those. Just allowlist that package for now (2024-07-10).
-			continue
-		}
 		if len(ff) > 1 {
-			t.Logf("multiple files with package doc in %s: %q", dir, ff)
+			t.Errorf("multiple files with package doc in %s: %q", dir, ff)
 		}
 		if len(ff) == 0 {
 			if strings.HasPrefix(dir, "gokrazy/") {