show parser warnings when there are parser errors

Author: lrytz

Diff for: compiler/src/dotty/tools/dotc/Run.scala

@@ -140,10 +140,11 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
       mySuspendedMessages.remove(source).foreach(_.foreach(ctx.reporter.issueIfNotSuppressed))
     }
 
-    def warnUnusedSuppressions(): Unit =
-      // if we stop before typer completes (errors in parser, Ystop), report all suspended messages
+    def runFinished(hasErrors: Boolean): Unit =
+      // report suspended messages (in case the run finished before typer)
       mySuspendedMessages.keysIterator.toList.foreach(reportSuspendedMessages)
-      if ctx.settings.WunusedHas.nowarn then
+      // report unused nowarns only if all all phases are done
+      if !hasErrors && ctx.settings.WunusedHas.nowarn then
         for {
           source <- mySuppressions.keysIterator.toList
           sups   <- mySuppressions.remove(source)
@@ -279,8 +280,7 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
     runPhases(using runCtx)
     if (!ctx.reporter.hasErrors)
       Rewrites.writeBack()
-      // later phases don't run when there are errors, which would lead to stale `unused @nowarn` warnings
-      suppressions.warnUnusedSuppressions()
+    suppressions.runFinished(hasErrors = ctx.reporter.hasErrors)
     while (finalizeActions.nonEmpty) {
       val action = finalizeActions.remove(0)
       action()

Diff for: tests/neg-custom-args/nowarn/nowarn-parser-error.check

@@ -0,0 +1,13 @@
+-- [E040] Syntax Error: tests/neg-custom-args/nowarn/nowarn-parser-error.scala:3:6 -------------------------------------
+3 |  def def // error
+  |      ^^^
+  |      an identifier expected, but 'def' found
+
+longer explanation available when compiling with `-explain`
+-- [E000] Syntax Warning: tests/neg-custom-args/nowarn/nowarn-parser-error.scala:2:10 ----------------------------------
+2 |  def a = try 1 // warn
+  |          ^^^^^
+  |          A try without catch or finally is equivalent to putting
+  |          its body in a block; no exceptions are handled.
+
+longer explanation available when compiling with `-explain`

Diff for: tests/neg-custom-args/nowarn/nowarn-parser-error.scala

@@ -0,0 +1,4 @@
+class C {
+  def a = try 1 // warn
+  def def // error
+}

Diff for: tests/neg-custom-args/nowarn/nowarn-typer-error.check

@@ -0,0 +1,6 @@
+-- [E006] Not Found Error: tests/neg-custom-args/nowarn/nowarn-typer-error.scala:4:11 ----------------------------------
+4 |  def t1 = / // error
+  |           ^
+  |           Not found: /
+
+longer explanation available when compiling with `-explain`

Diff for: tests/neg-custom-args/nowarn/nowarn-typer-error.scala

@@ -0,0 +1,7 @@
+import annotation.nowarn
+object T {
+  @deprecated def f = 1
+  def t1 = / // error
+  @nowarn    // unused-nowarn is not issued if earlier phase has an error.
+  def t2 = f // no warning, refchecks doesn't run if typer has an error
+}