Add a `dotty-interfaces` package

We introduce a new entry point for the compiler in
`dotty.tools.dotc.Driver`:
```
def process(args: Array[String], simple: interfaces.SimpleReporter,
  callback: interfaces.CompilerCallback): interfaces.ReporterResult
```
Except for `args` which is just an array, the argument types and return
type of this method are Java interfaces defined in a new package called
`dotty-interfaces` which has a stable ABI. This means that you can
programmatically run a compiler with a custom reporter and callbacks
without having to recompile it against every version of dotty: you only
need to have `dotty-interfaces` present at compile-time and call the
`process` method using Java reflection.

See `test/test/InterfaceEntryPointTest.scala` for a concrete example.

This design is based on discussions with the IntelliJ IDEA Scala plugin
team. Thanks to Nikolay Tropin for the discussions and his PR
proposal (see #1011).

1 files changed, 44 insertions, 0 deletions

diff --git a/interfaces/src/main/java/dotty/tools/dotc/interfaces/SourcePosition.java b/interfaces/src/main/java/dotty/tools/dotc/interfaces/SourcePosition.java
new file mode 100644
index 000000000..c9b42d4ad
--- /dev/null
+++ b/interfaces/src/main/java/dotty/tools/dotc/interfaces/SourcePosition.java
@@ -0,0 +1,44 @@
+package dotty.tools.dotc.interfaces;
+
+/** A position in a source file.
+ *
+ *  A position is a range between a start offset and an end offset, as well as a
+ *  point inside this range.
+ *
+ *  As a convenience, we also provide methods that return the line and the column
+ *  corresponding to each offset.
+ *
+ *  User code should not implement this interface, but it may have to
+ *  manipulate objects of this type.
+ */
+public interface SourcePosition {
+  /** Content of the line which contains the point */
+  String lineContent();
+
+  /** Offset to the point */
+  int point();
+  /** Line number of the point, starting at 0 */
+  int line();
+  /** Column number of the point, starting at 0 */
+  int column();
+
+  /** Offset to the range start */
+  int start();
+  /** Line number of the range start, starting at 0 */
+  int startLine();
+  /** Column number of the range start, starting at 0 */
+  int startColumn();
+
+  /** Offset to the range end */
+  int end();
+  /** Line number of the range end, starting at 0 */
+  int endLine();
+  /** Column number of the range end, starting at 0 */
+  int endColumn();
+
+  /** The source file corresponding to this position.
+   *  The values returned by `point()`, `start()` and `end()`
+   *  are indices in the array returned by `source().content()`.
+   */
+  SourceFile source();
+}