From d6cf0578a83cc0248fc69ff6fee7f1ce402aa0b5 Mon Sep 17 00:00:00 2001
From: Wojciech Mazur <wmazur@virtuslab.com>
Date: Tue, 21 Oct 2025 11:52:25 +0200
Subject: [PATCH] Deduplicate patches before applying them to sources (#24215)

Fixes #24213 - deduplicate patches by content and span.

Similar issues were spotted for code `using` rewrites resulting in
invalid `using using` introduced by compiler.
Issue might arise if some reason compiler typechecks the same code twice
[Cherry-picked 2af74542b628e8e04d17e5d202f8258bd6417692]
---
 compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala | 4 ++--
 compiler/test/dotty/tools/dotc/CompilationTests.scala | 1 +
 tests/rewrites/i24213.check                           | 5 +++++
 tests/rewrites/i24213.scala                           | 5 +++++
 4 files changed, 13 insertions(+), 2 deletions(-)
 create mode 100644 tests/rewrites/i24213.check
 create mode 100644 tests/rewrites/i24213.scala

diff --git a/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala b/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala
index 272db26bdd3c..da6788901f0d 100644
--- a/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala
+++ b/compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala
@@ -43,8 +43,8 @@ object Rewrites {
       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)
+      val patches = pbuf.toList.distinct.sortBy(_.span.start)
+      val delta = patches.map(_.delta).sum
       if (patches.nonEmpty)
         patches.reduceLeft {(p1, p2) =>
           assert(p1.span.end <= p2.span.start, s"overlapping patches in $source: $p1 and $p2")
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index de200a0f774a..cb8768a1cb81 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -89,6 +89,7 @@ class CompilationTests {
       compileFile("tests/rewrites/implicit-to-given.scala", defaultOptions.and("-rewrite", "-Yimplicit-to-given")),
       compileFile("tests/rewrites/i22792.scala", defaultOptions.and("-rewrite")),
       compileFile("tests/rewrites/i23449.scala", defaultOptions.and("-rewrite", "-source:3.4-migration")),
+      compileFile("tests/rewrites/i24213.scala", defaultOptions.and("-rewrite", "-source:3.4-migration")),
     ).checkRewrites()
   }
 
diff --git a/tests/rewrites/i24213.check b/tests/rewrites/i24213.check
new file mode 100644
index 000000000000..d06d2f63c7c2
--- /dev/null
+++ b/tests/rewrites/i24213.check
@@ -0,0 +1,5 @@
+def Test =
+  try ()
+  catch {
+    case x: Throwable if x.getMessage `contains` "error" => ???
+  }
\ No newline at end of file
diff --git a/tests/rewrites/i24213.scala b/tests/rewrites/i24213.scala
new file mode 100644
index 000000000000..49148abace00
--- /dev/null
+++ b/tests/rewrites/i24213.scala
@@ -0,0 +1,5 @@
+def Test =
+  try ()
+  catch {
+    case x: Throwable if x.getMessage contains "error" => ???
+  }
\ No newline at end of file