Build layout

sbt uses conventions for file placement to make it easy to dive into a new sbt build:

.
├── build.sbt
├── project/
│   ├── build.properties
│   ├── Dependencies.scala
│   └── plugins.sbt
├── src/
│   ├── main/
│   │   ├── java/
│   │   ├── resources/
│   │   ├── scala/
│   │   └── scala-2.13/
│   └── test/
│       ├── java/
│       ├── resources/
│       ├── scala/
│       └── scala-2.13/
├── subproject-core/
│   └── src/
│       ├── main/
│       └── test/
├─── subproject-util/
│   └── src/
│       ├── main/
│       └── test/
└── target/

• The local root directory . is the starting point of your build.
• In sbt's terminology, the base directory is the directory containing the subproject. In the above, ., subproject-core, and subproject-util are base directories.
• The build definition is described in build.sbt (actually any files named *.sbt) in the local root directory.
• The sbt version is tracked in project/build.properties.
• Generated files (compiled classes, packaged jars, managed files, caches, and documentation) will be written to the target directory by default.

Build support files

In addition to build.sbt, project directory can contain .scala files that define helper objects and one-off plugins.

.
├── build.sbt
├── project/
│   ├── build.properties
│   ├── Dependencies.scala
│   └── plugins.sbt
....

You may see .sbt files inside project/, which is typically used to declare plugins. See Plugin basics.

Source code

sbt uses the same directory structure as Maven for source files by default (all paths are relative to the base directory):

....
├── src/
│   ├── main/
│   │   ├── java/        <main Java sources>
│   │   ├── resources/   <files to include in main JAR>
│   │   ├── scala/       <main Scala sources>
│   │   └── scala-2.13/  <main Scala 2.13 specific sources>
│   └── test/
│       ├── java/        <test Java sources>
│       ├── resources/   <files to include in test JAR>
│       ├── scala/       <test Scala sources>
│       └── scala-2.13/  <test Scala 2.13 specific sources>
....

Other directories in src/ will be ignored. Additionally, all hidden directories will be ignored.

Source code can be placed in the project's base directory as hello/app.scala, which may be OK for small projects, though for normal projects people tend to keep the projects in the src/main/ directory to keep things neat.

Configuring version control

Your .gitignore (or equivalent for other version control systems) should contain:

target/