scala-macro-debug

Scala macros to make debugging easier.

Comes in two flavors, DebugMacros, as described on the blog (see introduction below), and an enhanced version DebugConsole.

DebugMacros example:

class Test {
    import com.softwaremill.debug.DebugMacros._

    val v1 = 10

    def test() {
        val v2 = 20
        debug("Values in test", v1, v2)
    }
}

Should print:

Values in test, Test.this.v1 = 10, v2 = 20

DebugConsole example:

class Test {
    import com.softwaremill.debug.DebugConsole._

    val v1 = 10

    def test() {
        val v2 = 20
        debug("Values in test", v1, v2)
    }
}

Should print:

|D| Values in test, Test.this.v1 = 10, v2 = 20

And:

class Test {
    import com.softwaremill.debug.DebugConsole._

    val v1 = 10

    def test() {
        val v2 = 20
        debugReport("Values in test", v1, v2)
    }
}

Should print:

|D| Values in test
|D|     Test.this.v1 = 10
|D|     v2           = 20

Features

• Two Modes: debug (dynamic single line debugging message) and debugReport (title and variables report)
• Can be disabled at compile time (the debugging code is removed from the final .class files)
• Can be used to print the current source code file name and line
• Really easy to use (there are only two methods)

Introduction

We all use println messages to debug our code and check the execution flow. And we quickly end up with things like this:

println("Values in test, Test.this.v1 = " + v1 + ", v2 = " + v2)

And this is only for two variables. It can quickly grow ugly. And also, hunting down all the lost println lines lost in the middle of the code ends up being nightmarish.

This project is the brainchild of a tutorial to learn to code Scala Macros. See the blog: "Starting with Scala Macros: a short tutorial".

Getting the Project: SBT

To use in your project, add the following dependency:

"com.softwaremill.scalamacrodebug" %% "macros" % "0.3" // scala 2.10
"com.softwaremill.scalamacrodebug" %% "macros" % "0.4.1" // scala 2.11, 2.12 and 2.13

Getting the Project: Maven

To use in your project, add the following dependency:

<dependency>
    <groupId>com.softwaremill.scalamacrodebug</groupId>
    <artifactId>macros_2.11</artifactId>
    <version>0.4</version>
</dependency>

Usage

Always include:

import com.softwaremill.debug.DebugMacros._

Or:

import com.softwaremill.debug.DebugConsole._

You can also extend the DebugMacros or DebugConsole traits in your util-object/package-object, if you have such an object which you frequently import (then debug will be easily available without additional imports).

The great strength of the debug methods is the ability to create a label for an expression to be debugged:

debug(a + b)

prints:

|D| a.+(b) = 30

You can combine as many as you want:

debug(a + b, c, 7 + 3)

prints:

|D| a.+(b) = 30, c = 14, 7.+(3) = 10

You can also mix as many constant literals (typically a String) as you want. They would be left untouched:

debug(a + b, "which should be different from", 7 + 3)

prints:

|D| a.+(b) = 30, which should be different from, 7.+(3)

The debugReport method prints the expressions debug with one expression per line:

debugReport(a + b, c, 7 + 3)

prints:

|D| a.+(b) = 30
|D| c      = 14
|D| 7.+(3) = 10

With an optional title as the first parameter:

debugReport("And the set of vars is:", a + b, c, 7 + 3)

prints:

|D| And the set of vars is:
|D|     a.+(b) = 30
|D|     c      = 14
|D|     7.+(3) = 10

And finally, if you do:

debug()

or

debugReport()

You will get a debug message that reports the Source File and Line this call is placed in.

Disabling

One of the strengths of the library is that it can be disabled on compile time. And if you disable it, all the debug and debugReport calls are literally removed from the generated code. You will no longer need to hunt down all the println sentences lost in the middle of the code.

To do this, you can set the environment variable enable_debug_messages to false (it's considered to be true by default). You can also send it as a system property (the system property takes precedence over the environment variable).