Generate API documentation 

Select javadoc or scaladoc 

sbt will run javadoc if there are only Java sources in the project. If there are any Scala sources, sbt will run scaladoc. (This situation results from scaladoc not processing Javadoc comments in Java sources nor linking to Javadoc.)

Set the options used for generating scaladoc independently of compilation 

Scope scalacOptions to the doc task to configure scaladoc. Use := to definitively set the options without appending to the options for compile. Scope to Compile for main sources or to Test for test sources. For example,

Compile / doc / scalacOptions := Seq("-groups", "-implicits")

Add options for scaladoc to the compilation options 

Scope scalacOptions to the doc task to configure scaladoc. Use += or ++= to append options to the base options. To append a single option, use +=. To append a Seq[String], use ++=. Scope to Compile for main sources or to Test for test sources. For example,

Compile / doc / scalacOptions ++= Seq("-groups", "-implicits")

Set the options used for generating javadoc independently of compilation 

Scope javacOptions to the doc task to configure javadoc. Use := to definitively set the options without appending to the options for compile. Scope to Compile for main sources or to Test for test sources.

Add options for javadoc to the compilation options 

Scope javacOptions to the doc task to configure javadoc. Use += or ++= to append options to the base options. To append a single option, use +=. To append a Seq[String], use ++=. Scope to Compile for main sources or to Test for test sources. For example,

Compile / doc / javacOptions ++= Seq("-notimestamp", "-linksource")

Enable automatic linking to the external Scaladoc of managed dependencies 

Set autoAPIMappings := true for sbt to tell scaladoc where it can find the API documentation for managed dependencies. This requires that dependencies have this information in its metadata and you are using scaladoc for Scala 2.10.2 or later.

Enable manual linking to the external Scaladoc of managed dependencies 

Add mappings of type (File, URL) to apiMappings to manually tell scaladoc where it can find the API documentation for dependencies. (This requires scaladoc for Scala 2.10.2 or later.) These mappings are used in addition to autoAPIMappings, so this manual configuration is typically done for unmanaged dependencies. The File key is the location of the dependency as passed to the classpath. The URL value is the base URL of the API documentation for the dependency. For example,

apiMappings += (
  (unmanagedBase.value / "a-library.jar") -> 
    url("https://example.org/api/")
)

Define the location of API documentation for a library 

Set apiURL to define the base URL for the Scaladocs for your library. This will enable clients of your library to automatically link against the API documentation using autoAPIMappings. (This only works for Scala 2.10.2 and later.) For example,

apiURL := Some(url("https://example.org/api/"))

This information will get included in a property of the published pom.xml, where it can be automatically consumed by sbt.