mttkay / debugging-scala-implicits-in-intellij

How to debug Scala implicit conversions and parameters in IntelliJ

Debugging Scala Implicits in IntelliJ

This document outlines several complementary approaches for statically analysing Scala implicits in IntelliJ.

JetBrains provides a document explaining the first two steps, but does not include the clarification around analysing enriched objects.

Note: These shortcuts are for OSX.

Viewing implicit conversions

1. Highlight the implicitly converted object.

   Important: When investigating an enriched object, you MUST highlight the object only, NOT the injected method. This is because the object is what's being converted; selecting the method will resolve implicit conversions on the object returned by that method.

2. CTRL + Q

Viewing actual implicit parameters

1. Highlight the method call-site.

2. CMD + SHIFT + P

See Viewing code without implicits if you receive 'Parameter not found'

Viewing actual implicit parameters on implicit conversions

The following requires temporary code modification:

1. Perform steps in Viewing implicit conversions.

2. Highlight appropriate implicit conversion function.

3. ALT + ENTER (and then ENTER to select 'Make explicit').

4. Perform steps in Viewing actual implicit parameters.

Viewing code without implicits

This is the last resort: it displays the 'unravelled' Scala code, which is useful if you don't have IntelliJ or IntelliJ is unable to resolve implicit parameters:

1. Run from the command line:

   sbt "set scalacOptions in Compile += \"-Xprint:typer\"" "compile"
   

2. Ignore the initial output.

3. 'Touch' the file you are interested in.

4. Re-run step 1.