Merge pull request #14738 from dotty-staging/fix-14721

Warn on misleading indentation in single-case catch

Author: odersky

compiler/src/dotty/tools/backend/jvm/BytecodeWriters.scala

@@ -117,7 +117,8 @@ trait BytecodeWriters {
       catch case ex: ClosedByInterruptException =>
         try
           outfile.delete() // don't leave an empty or half-written classfile around after an interrupt
-        catch case _: Throwable =>
+        catch
+          case _: Throwable =>
         throw ex
       finally outstream.close()
       report.informProgress("wrote '" + label + "' to " + outfile)

compiler/src/dotty/tools/backend/jvm/GenBCode.scala

@@ -275,7 +275,8 @@ class GenBCodePipeline(val int: DottyBackendInterface, val primitives: DottyPrim
             catch case ex: ClosedByInterruptException =>
               try
                 outTastyFile.delete() // don't leave an empty or half-written tastyfile around after an interrupt
-              catch case _: Throwable =>
+              catch
+                case _: Throwable =>
               throw ex
             finally outstream.close()
 

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2617,7 +2617,14 @@ object Parsers {
         (pattern(), guard())
       }
       CaseDef(pat, grd, atSpan(accept(ARROW)) {
-        if exprOnly then expr() else block()
+        if exprOnly then
+          if in.indentSyntax && in.isAfterLineEnd && in.token != INDENT then
+            warning(i"""Misleading indentation: this expression forms part of the preceding catch case.
+                       |If this is intended, it should be indented for clarity.
+                       |Otherwise, if the handler is intended to be empty, use a multi-line catch with
+                       |an indented case.""")
+          expr()
+        else block()
       })
     }
 

compiler/test/dotty/tools/repl/ShadowingTests.scala

@@ -33,7 +33,7 @@ object ShadowingTests:
     val subdir = dir.resolve(name)
     try Files.createDirectory(subdir)
     catch case _: java.nio.file.FileAlreadyExistsException =>
-    assert(Files.isDirectory(subdir), s"failed to create shadowed subdirectory $subdir")
+      assert(Files.isDirectory(subdir), s"failed to create shadowed subdirectory $subdir")
     subdir
 
   // The directory on the classpath containing artifacts to be shadowed

tests/neg-custom-args/fatal-warnings/i14721.scala

@@ -0,0 +1,8 @@
+
+class C:
+  def op: Unit = println("op")
+  def handler: Unit = println("handler")
+  def test: Unit =
+    try op
+    catch case _: NullPointerException =>
+    handler   // error