Issue unused nowarn warning only if the compiler run has no errors

Author: lrytz

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

@@ -270,12 +270,14 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
     runCtx.setProfiler(Profiler())
     unfusedPhases.foreach(_.initContext(runCtx))
     runPhases(using runCtx)
-    if (!ctx.reporter.hasErrors) Rewrites.writeBack()
+    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()
     while (finalizeActions.nonEmpty) {
       val action = finalizeActions.remove(0)
       action()
     }
-    suppressions.warnUnusedSuppressions()
     compiling = false
   }
 

Diff for: compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -128,7 +128,7 @@ class CompilationTests {
       compileFilesInDir("tests/neg-no-kind-polymorphism", defaultOptions and "-Yno-kind-polymorphism"),
       compileFilesInDir("tests/neg-custom-args/deprecation", defaultOptions.and("-Xfatal-warnings", "-deprecation")),
       compileFilesInDir("tests/neg-custom-args/fatal-warnings", defaultOptions.and("-Xfatal-warnings")),
-      compileFilesInDir("tests/neg-custom-args/nowarn", defaultOptions.and("-deprecation", "-Werror", "-Wunused:nowarn")),
+      compileFilesInDir("tests/neg-custom-args/nowarn", defaultOptions.and("-deprecation", "-Wunused:nowarn", "-Wconf:msg=@nowarn annotation does not suppress any warnings:e")),
       compileFilesInDir("tests/neg-custom-args/erased", defaultOptions.and("-language:experimental.erasedDefinitions")),
       compileFilesInDir("tests/neg-custom-args/allow-double-bindings", allowDoubleBindings),
       compileFilesInDir("tests/neg-custom-args/allow-deep-subtypes", allowDeepSubtypes),

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

@@ -0,0 +1,63 @@
+-- [E000] Syntax Warning: tests/neg-custom-args/nowarn/nowarn.scala:9:10 -----------------------------------------------
+9 |def t1a = try 1 // warning (parser)
+  |          ^^^^^
+  |          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`
+-- [E000] Syntax Warning: tests/neg-custom-args/nowarn/nowarn.scala:21:26 ----------------------------------------------
+21 |@nowarn("id=1") def t4d = try 1 // error and warning (unused nowarn, wrong id)
+   |                          ^^^^^
+   |                          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`
+-- [E000] Syntax Warning: tests/neg-custom-args/nowarn/nowarn.scala:23:28 ----------------------------------------------
+23 |@nowarn("verbose") def t5 = try 1 // warning with details
+   |                            ^^^^^
+   |                            A try without catch or finally is equivalent to putting
+   |                            its body in a block; no exceptions are handled.
+Matching filters for @nowarn or -Wconf:
+  - id=E0
+  - name=EmptyCatchOrFinallyBlock
+
+longer explanation available when compiling with `-explain`
+-- [E129] Potential Issue Warning: tests/neg-custom-args/nowarn/nowarn.scala:13:11 -------------------------------------
+13 |def t2 = { 1; 2 } // warning (the invalid nowarn doesn't silence anything)
+   |           ^
+   |           A pure expression does nothing in statement position; you may be omitting necessary parentheses
+
+longer explanation available when compiling with `-explain`
+-- Warning: tests/neg-custom-args/nowarn/nowarn.scala:12:8 -------------------------------------------------------------
+12 |@nowarn("wat?") // warning (typer, invalid filter)
+   |        ^^^^^^
+   |        Invalid message filter
+   |        unknown filter: wat?
+-- Deprecation Warning: tests/neg-custom-args/nowarn/nowarn.scala:27:10 ------------------------------------------------
+27 |def t6a = f // warning (refchecks, deprecation)
+   |          ^
+   |          method f is deprecated
+-- Deprecation Warning: tests/neg-custom-args/nowarn/nowarn.scala:30:30 ------------------------------------------------
+30 |@nowarn("msg=fish") def t6d = f // error (unused nowarn), warning (deprecation)
+   |                              ^
+   |                              method f is deprecated
+-- Deprecation Warning: tests/neg-custom-args/nowarn/nowarn.scala:37:10 ------------------------------------------------
+37 |def t7c = f:          // warning (deprecation)
+   |          ^
+   |          method f is deprecated
+-- Unchecked Warning: tests/neg-custom-args/nowarn/nowarn.scala:43:7 ---------------------------------------------------
+43 |  case _: List[Int] => 0 // warning (patmat, unchecked)
+   |       ^
+   |       the type test for List[Int] cannot be checked at runtime
+-- Error: tests/neg-custom-args/nowarn/nowarn.scala:21:1 ---------------------------------------------------------------
+21 |@nowarn("id=1") def t4d = try 1 // error and warning (unused nowarn, wrong id)
+   |^^^^^^^^^^^^^^^
+   |@nowarn annotation does not suppress any warnings
+-- Error: tests/neg-custom-args/nowarn/nowarn.scala:30:1 ---------------------------------------------------------------
+30 |@nowarn("msg=fish") def t6d = f // error (unused nowarn), warning (deprecation)
+   |^^^^^^^^^^^^^^^^^^^
+   |@nowarn annotation does not suppress any warnings
+-- Error: tests/neg-custom-args/nowarn/nowarn.scala:38:3 ---------------------------------------------------------------
+38 |  @nowarn("msg=fish") // error (unused nowarn)
+   |  ^^^^^^^^^^^^^^^^^^^
+   |  @nowarn annotation does not suppress any warnings

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

@@ -0,0 +1,48 @@
+import annotation.nowarn
+
+// This test doesn't run with `-Werror`, because once there's an error, later phases are skipped and we would not see
+// their warnings.
+// Instead, this test runs with `-Wunused:nowarn -Wconf:msg=@nowarn annotation does not suppress any warnings:e`.
+// Only "unused nowarn" warnings are reported as errors. Since these warnings are reported at the very end, all other
+// phases of the compiler run normally.
+
+def t1a = try 1 // warning (parser)
+@nowarn("msg=try without catch") def t1b = try 1
+
+@nowarn("wat?") // warning (typer, invalid filter)
+def t2 = { 1; 2 } // warning (the invalid nowarn doesn't silence anything)
+
+@nowarn("id=E129") def t3a = { 1; 2 }
+@nowarn("name=PureExpressionInStatementPosition") def t3b = { 1; 2 }
+
+@nowarn("id=E000") def t4a = try 1
+@nowarn("id=E0") def t4b = try 1
+@nowarn("id=0") def t4c = try 1
+@nowarn("id=1") def t4d = try 1 // error and warning (unused nowarn, wrong id)
+
+@nowarn("verbose") def t5 = try 1 // warning with details
+
+@deprecated def f = 0
+
+def t6a = f // warning (refchecks, deprecation)
+@nowarn("cat=deprecation") def t6b = f
+@nowarn("msg=deprecated") def t6c = f
+@nowarn("msg=fish") def t6d = f // error (unused nowarn), warning (deprecation)
+@nowarn("") def t6e = f
+@nowarn def t6f = f
+
+def t7a = f: @nowarn("cat=deprecation")
+def t7b = f:
+  @nowarn("msg=deprecated")
+def t7c = f:          // warning (deprecation)
+  @nowarn("msg=fish") // error (unused nowarn)
+def t7d = f: @nowarn("")
+def t7e = f: @nowarn
+
+def t8a(x: Any) = x match
+  case _: List[Int] => 0 // warning (patmat, unchecked)
+  case _ => 1
+
+@nowarn("cat=unchecked") def t8(x: Any) = x match
+  case _: List[Int] => 0
+  case _ => 1