From 7a578677d516486d3b96eafba32fd1e3951df148 Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Fri, 16 Aug 2024 09:03:21 -0700
Subject: [PATCH] Undo patch of double-block apply

If `f{}{}` is candidate for rewrite, unpatch it.

We don't know exact spans, so just check endpoints to remove.
---
 .../src/dotty/tools/dotc/parsing/Parsers.scala  |  8 +++++++-
 .../dotty/tools/dotc/rewrites/Rewrites.scala    | 17 ++++++++++++++++-
 .../dotty/tools/dotc/CompilationTests.scala     |  1 +
 tests/rewrites/i21382.scala                     |  8 ++++++++
 4 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 tests/rewrites/i21382.scala

diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index 2e441553689c..6aa55a61dc2b 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -27,7 +27,7 @@ import ScriptParsers.*
 import Decorators.*
 import util.Chars
 import scala.annotation.tailrec
-import rewrites.Rewrites.{patch, overlapsPatch}
+import rewrites.Rewrites.{overlapsPatch, patch, unpatch}
 import reporting.*
 import config.Feature
 import config.Feature.{sourceVersion, migrateTo3}
@@ -2779,6 +2779,12 @@ object Parsers {
           simpleExprRest(tapp, location, canApply = true)
         case LPAREN | LBRACE | INDENT if canApply =>
           val app = atSpan(startOffset(t), in.offset) { mkApply(t, argumentExprs()) }
+          if in.rewriteToIndent then
+            app match
+              case Apply(Apply(_, List(Block(_, _))), List(blk @ Block(_, _))) =>
+                unpatch(blk.srcPos.sourcePos.source, Span(blk.span.start, blk.span.start + 1))
+                unpatch(blk.srcPos.sourcePos.source, Span(blk.span.end, blk.span.end + 1))
+              case _ =>
           simpleExprRest(app, location, canApply = true)
         case USCORE =>
           atSpan(startOffset(t), in.skipToken()) { PostfixOp(t, Ident(nme.WILDCARD)) }
diff --git a/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala b/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala
index 305f61dfa177..ebc50059a39e 100644
--- a/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala
+++ b/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala
@@ -32,11 +32,16 @@ object Rewrites {
   case class ActionPatch(srcPos: SourcePosition, replacement: String)
 
   private class Patches(source: SourceFile) {
-    private[Rewrites] val pbuf = new mutable.ListBuffer[Patch]()
+    private[Rewrites] val pbuf = mutable.ListBuffer.empty[Patch]
 
     def addPatch(span: Span, replacement: String): Unit =
       pbuf += Patch(span, replacement)
 
+    // remove patches which match either end point
+    def removePatch(span: Span): Unit =
+      def p(other: Span): Boolean = span.start == other.start || span.end == other.end
+      pbuf.filterInPlace(x => !p(x.span))
+
     def apply(cs: Array[Char]): Array[Char] = {
       val delta = pbuf.map(_.delta).sum
       val patches = pbuf.toList.sortBy(_.span.start)
@@ -87,6 +92,16 @@ object Rewrites {
   def patch(span: Span, replacement: String)(using Context): Unit =
     patch(ctx.compilationUnit.source, span, replacement)
 
+  /** Delete patches matching the given span,
+   *  where a match has the same start or end offset.
+   */
+  def unpatch(source: SourceFile, span: Span)(using Context): Unit =
+    if ctx.reporter != Reporter.NoReporter // NoReporter is used for syntax highlighting
+    then ctx.settings.rewrite.value.foreach: rewrites =>
+      rewrites.patched
+        .get(source)
+        .foreach(_.removePatch(span))
+
   /** Does `span` overlap with a patch region of `source`? */
   def overlapsPatch(source: SourceFile, span: Span)(using Context): Boolean =
     ctx.settings.rewrite.value.exists(rewrites =>
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index 3bd3b5138fad..9aa533bed0e4 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -80,6 +80,7 @@ class CompilationTests {
       compileDir("tests/rewrites/annotation-named-pararamters", defaultOptions.and("-rewrite", "-source:3.6-migration")),
       compileFile("tests/rewrites/i21418.scala", unindentOptions.and("-rewrite", "-source:3.5-migration")),
       compileFile("tests/rewrites/infix-named-args.scala", defaultOptions.and("-rewrite", "-source:3.6-migration")),
+      compileFile("tests/rewrites/i21382.scala", defaultOptions.and("-indent", "-rewrite")),
     ).checkRewrites()
   }
 
diff --git a/tests/rewrites/i21382.scala b/tests/rewrites/i21382.scala
new file mode 100644
index 000000000000..75f4007be218
--- /dev/null
+++ b/tests/rewrites/i21382.scala
@@ -0,0 +1,8 @@
+def check(element: Any)(expected: String): Unit = ???
+
+def test =
+  check {
+    ???
+  }{
+    42.toString
+  }