doc(buildtool): explain ANDROID_NDK_HOME for android gomobile

Part of ooni/probe#2273

internal/cmd/buildtool/android.go

@@ -68,6 +68,13 @@ func androidBuildGomobile(deps buildtoolmodel.Dependencies) {
 
 	envp := &shellx.Envp{}
 	envp.Append("ANDROID_HOME", androidHome)
+
+	// From the gomobile repository:
+	//
+	//	Try the ANDROID_NDK_HOME variable.  This approach is deprecated, but it has
+	//	the highest priority because it represents an explicit user choice.
+	//
+	// See https://github.com/golang/mobile/blob/8578da983/cmd/gomobile/env.go#L394
 	envp.Append("ANDROID_NDK_HOME", ndkDir)
 
 	config := &gomobileConfig{

internal/cmd/buildtool/builddeps.go

@@ -1,5 +1,10 @@
 package main
 
+//
+// Allows unit testing build rules by abstracting
+// specific activities through an interface.
+//
+
 import (
 	"io/fs"
 

internal/cmd/buildtool/cdepslibevent.go

@@ -5,6 +5,7 @@ package main
 //
 // Adapted from https://github.com/guardianproject/tor-android
 // SPDX-License-Identifier: BSD-3-Clause
+//
 
 import (
 	"path/filepath"

internal/cmd/buildtool/cdepsopenssl.go

@@ -5,6 +5,7 @@ package main
 //
 // Adapted from https://github.com/guardianproject/tor-android
 // SPDX-License-Identifier: BSD-3-Clause
+//
 
 import (
 	"os"

internal/cmd/buildtool/cdepstor.go

@@ -5,6 +5,7 @@ package main
 //
 // Adapted from https://github.com/guardianproject/tor-android
 // SPDX-License-Identifier: BSD-3-Clause
+//
 
 import (
 	"path/filepath"

internal/cmd/buildtool/cdepszlib.go

@@ -5,6 +5,7 @@ package main
 //
 // Adapted from https://github.com/guardianproject/tor-android
 // SPDX-License-Identifier: BSD-3-Clause
+//
 
 import (
 	"path/filepath"

internal/cmd/buildtool/linuxdocker.go

@@ -1,5 +1,9 @@
 package main
 
+//
+// Building for linux-static using docker and alpine.
+//
+
 import (
 	"fmt"
 	"os"

internal/cmd/buildtool/linuxstatic.go

@@ -1,7 +1,8 @@
 package main
 
 //
-// Builds for Linux assuming static linking makes sense.
+// Builds for Linux assuming static linking makes sense and
+// also assuming we're in a docker container.
 //
 
 import (

internal/cmd/buildtool/main.go

@@ -16,12 +16,14 @@ func main() {
 		Use:   "buildtool",
 		Short: "Tool for building ooniprobe, miniooni, etc.",
 	}
+
 	root.AddCommand(androidSubcommand())
 	root.AddCommand(darwinSubcommand())
 	root.AddCommand(genericSubcommand())
 	root.AddCommand(iosSubcommand())
 	root.AddCommand(linuxSubcommand())
 	root.AddCommand(windowsSubcommand())
+
 	logHandler := logx.NewHandlerWithDefaultSettings()
 	logHandler.Emoji = true
 	log.Log = &log.Logger{Level: log.InfoLevel, Handler: logHandler}

internal/cmd/buildtool/product.go

@@ -1,7 +1,7 @@
 package main
 
 //
-// Defines the products we can build
+// Defines the CLI products we can build
 //
 
 import (

internal/cmd/buildtool/windows.go

@@ -1,7 +1,7 @@
 package main
 
 //
-// Windows build
+// Windows cross build using mingw-w64
 //
 
 import (