better ergnomics for -Yno-suspended-units

Author: bishabosha

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

@@ -97,15 +97,12 @@ class CompilationUnit protected (val source: SourceFile, val info: CompilationUn
     // when this unit is unsuspended.
     depRecorder.clear()
     if !suspended then
-      if ctx.settings.YnoSuspendedUnits.value then
-        report.error(i"Compilation unit suspended $this (-Yno-suspended-units is set)")
-      else
-        if (ctx.settings.XprintSuspension.value)
-          report.echo(i"suspended: $this")
-        suspended = true
-        ctx.run.nn.suspendedUnits += this
-        if ctx.phase == Phases.inliningPhase then
-          suspendedAtInliningPhase = true
+      if ctx.settings.XprintSuspension.value then
+        report.echo(i"suspended: $this")
+      suspended = true
+      ctx.run.nn.suspendedUnits += this
+      if ctx.phase == Phases.inliningPhase then
+        suspendedAtInliningPhase = true
     throw CompilationUnit.SuspendException()
 
   private var myAssignmentSpans: Map[Int, List[Span]] | Null = null

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

@@ -1033,7 +1033,7 @@ class Inliner(val call: tpd.Tree)(using Context):
     }
   }
 
-  private def expandMacro(body: Tree, splicePos: SrcPos)(using Context) = {
+  private def expandMacro(body: Tree, splicePos: SrcPos)(using Context): Tree = {
     assert(level == 0)
     val inlinedFrom = enclosingInlineds.last
     val dependencies = macroDependencies(body)(using spliceContext)
@@ -1048,7 +1048,12 @@ class Inliner(val call: tpd.Tree)(using Context):
         if (suspendable && ctx.settings.XprintSuspension.value)
           report.echo(i"suspension triggered by macro call to ${sym.showLocated} in ${sym.associatedFile}", call.srcPos)
       if suspendable then
-        ctx.compilationUnit.suspend() // this throws a SuspendException
+        if ctx.settings.YnoSuspendedUnits.value then
+          return ref(defn.Predef_undefined)
+            .withType(ErrorType(em"could not expand macro, suspended units are disabled by -Yno-suspended-units"))
+            .withSpan(splicePos.span)
+        else
+          ctx.compilationUnit.suspend() // this throws a SuspendException
 
     val evaluatedSplice = inContext(quoted.MacroExpansion.context(inlinedFrom)) {
       Splicer.splice(body, splicePos, inlinedFrom.srcPos, MacroClassLoader.fromContext)

compiler/src/dotty/tools/dotc/quoted/Interpreter.scala

@@ -368,6 +368,9 @@ object Interpreter:
   }
 
   def suspendOnMissing(sym: Symbol, pos: SrcPos)(using Context): Nothing =
-    if ctx.settings.XprintSuspension.value then
-      report.echo(i"suspension triggered by a dependency on $sym", pos)
-    ctx.compilationUnit.suspend() // this throws a SuspendException
+    if ctx.settings.YnoSuspendedUnits.value then
+      throw StopInterpretation(em"suspension triggered by a dependency on missing $sym not allowed with -Yno-suspended-units", pos)
+    else
+      if ctx.settings.XprintSuspension.value then
+        report.echo(i"suspension triggered by a dependency on missing $sym", pos)
+      ctx.compilationUnit.suspend() // this throws a SuspendException