Make sharing violations errors

and use ctx.log for other output.

Author: odersky

src/dotty/tools/dotc/transform/CheckReentrant.scala

@@ -22,10 +22,23 @@ import NameOps._
 import StdNames._
 
 
-/** The first tree transform
- *   - ensures there are companion objects for all classes except module classes
- *   - eliminates some kinds of trees: Imports, NamedArgs
- *   - stubs out native methods
+/** A no-op transform that checks whether the compiled sources are re-entrant.
+ *  If -Ycheck:reentrant is set, the phase makes sure that there are no variables
+ *  that are accessible from a global object. It excludes from checking paths that
+ *  are labeled with one of the annotations
+ *
+ *      @sharable   Indicating a class or val can be safely shared
+ *      @unshared   Indicating an object will not be accessed from multiple threads
+ *
+ *  Currently the analysis is only intended to check the dotty compiler itself. To make
+ *  it generally useful we'd need to add at least the following:
+ *
+ *   - Handle polymorphic instantiation: We might instantiate a generic class
+ *     with a type that contains vars. If the class contains fields of the generic
+ *     type, this may constitute a path to a shared var, which currently goes undetected.
+ *   - Handle arrays: Array elements are currently ignored because they are often used
+ *     in an immutable way anyway. To do better, it would be helpful to have a type
+ *     for immutable array.
  */
 class CheckReentrant extends MiniPhaseTransform { thisTransformer =>
   import ast.tpd._
@@ -50,7 +63,7 @@ class CheckReentrant extends MiniPhaseTransform { thisTransformer =>
     sym.hasAnnotation(unsharedAnnot())
 
   def scanning(sym: Symbol)(op: => Unit)(implicit ctx: Context): Unit = {
-    println(i"${"  " * indent}scanning $sym")
+    ctx.log(i"${"  " * indent}scanning $sym")
     indent += 1
     try op
     finally indent -= 1
@@ -63,7 +76,9 @@ class CheckReentrant extends MiniPhaseTransform { thisTransformer =>
         for (sym <- cls.classInfo.decls)
           if (sym.isTerm && !sym.isSetter && !isIgnored(sym))
             if (sym.is(Mutable)) {
-              println(i"GLOBAL ${sym.showLocated}: ${sym.info} <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<")
+              ctx.error(
+                i"""possible data race involving globally reachable ${sym.showLocated}: ${sym.info}
+                   |  use -Ylog:checkReentrant+ to find out more about why the variable is reachable.""".stripMargin)
               shared += sym
             } else if (!sym.is(Method) || sym.is(Accessor | ParamAccessor)) {
               scanning(sym) {