Add -Xprint-suspension option to print info about suspensions

Author: odersky

compiler/src/dotty/tools/dotc/CompilationUnit.scala

@@ -37,7 +37,8 @@ class CompilationUnit protected (val source: SourceFile) {
 
   def suspend()(given ctx: Context): Nothing =
     if !suspended then
-      println(i"suspended: $this")
+      if (ctx.settings.XprintSuspension.value)
+        ctx.echo(i"suspended: $this")
       suspended = true
       ctx.run.suspendedUnits += this
     throw CompilationUnit.SuspendException()

compiler/src/dotty/tools/dotc/Driver.scala

@@ -10,6 +10,7 @@ import core.{MacroClassLoader, Mode, TypeError}
 import dotty.tools.dotc.ast.Positioned
 import dotty.tools.io.File
 import reporting._
+import core.Decorators._
 
 import scala.util.control.NonFatal
 import fromtasty.{TASTYCompiler, TastyFileUtil}
@@ -37,9 +38,12 @@ class Driver {
         def finish(run: Run): Unit =
           run.printSummary()
           if !ctx.reporter.errorsReported && run.suspendedUnits.nonEmpty then
+            val suspendedUnits = run.suspendedUnits.toList
+            if (ctx.settings.XprintSuspension.value)
+              ctx.echo(i"compiling suspended $suspendedUnits%, %")
             val run1 = compiler.newRun
-            for unit <- run.suspendedUnits do unit.suspended = false
-            run1.compileUnits(run.suspendedUnits.toList)
+            for unit <- suspendedUnits do unit.suspended = false
+            run1.compileUnits(suspendedUnits)
             finish(run1)
 
         finish(run)

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -77,6 +77,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val XprintDiff: Setting[Boolean] = BooleanSetting("-Xprint-diff", "Print changed parts of the tree since last print.")
   val XprintDiffDel: Setting[Boolean] = BooleanSetting("-Xprint-diff-del", "Print changed parts of the tree since last print including deleted parts.")
   val XprintInline: Setting[Boolean] = BooleanSetting("-Xprint-inline", "Show  where inlined code comes from")
+  val XprintSuspension: Setting[Boolean] = BooleanSetting("-Xprint-suspension", "Show when code is suspended until macros are compiled")
   val Xprompt: Setting[Boolean] = BooleanSetting("-Xprompt", "Display a prompt after each error (debugging option).")
   val XnoValueClasses: Setting[Boolean] = BooleanSetting("-Xno-value-classes", "Do not use value classes. Helps debugging.")
   val XreplLineWidth: Setting[Int] = IntSetting("-Xrepl-line-width", "Maximal number of columns per line for REPL output", 390)
@@ -200,7 +201,7 @@ class ScalaSettings extends Settings.SettingGroup {
     "The source repository of your project",
     ""
   )
-  
+
   val projectLogo: Setting[String] = StringSetting(
     "-project-logo",
     "project logo filename",

compiler/src/dotty/tools/dotc/typer/FrontEnd.scala

@@ -125,7 +125,9 @@ class FrontEnd extends Phase {
       ctx.error(em"""Cyclic macro dependencies $where
                     |Compilation stopped since no further progress can be made.
                     |
-                    |To fix this, place macros in one set of files and their callers in another.""")
+                    |To fix this, place macros in one set of files and their callers in another.
+                    |
+                    |Compiling with  -XprintSuspension   gives more information.""")
     newUnits
   }
 

compiler/src/dotty/tools/dotc/typer/Inliner.scala

@@ -1243,7 +1243,8 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(implicit ctx: Context) {
       for sym <- dependencies do
         if ctx.compilationUnit.source.file == sym.associatedFile then
           ctx.error(em"Cannot call macro $sym defined in the same source file", body.sourcePos)
-        println(i"suspension triggered by macro call to ${sym.showLocated} in ${sym.associatedFile}")
+        if (ctx.settings.XprintSuspension.value)
+          ctx.echo(i"suspension triggered by macro call to ${sym.showLocated} in ${sym.associatedFile}", body.sourcePos)
       ctx.compilationUnit.suspend() // this throws a SuspendException
 
     val evaluatedSplice = Splicer.splice(body, inlinedFrom.sourcePos, MacroClassLoader.fromContext)(ctx1)