[clang] 878ce21 - [clang-format] Propagate `LeadingEmptyLinesAffected` when joining lines (#146761)

[via cfe-commits]

Author: Eric Li
Date: 2025-07-05T17:06:59-04:00
New Revision: 878ce210e30f8ebcb4b73d834f91229a403e2376

URL: https://github.com/llvm/llvm-project/commit/878ce210e30f8ebcb4b73d834f91229a403e2376
DIFF: https://github.com/llvm/llvm-project/commit/878ce210e30f8ebcb4b73d834f91229a403e2376.diff

LOG: [clang-format] Propagate `LeadingEmptyLinesAffected` when joining lines (#146761)

Before this commit, when `LineJoiner` joins a line with affected leading
whitespace, it would drop the knowledge of this entirely. However, when
the `AffectedRangeManager` is computing the affected lines, the leading
empty whitespace lines are potentially considered for non-first tokens
in the `AnnotatedLine`. This causes a discrepancy in behavior when an
`AnnotatedLine` is put together from joining multiple lines versus when
it is not.

We change `LineJoiner::join` to follow `AffectedRangeManager`'s logic,
considering the leading whitespace when determining `Affected` for a
token.


https://github.com/llvm/llvm-project/blob/a63f57262898588b576d66e5fd79c0aa64b35f2d/clang/lib/Format/AffectedRangeManager.cpp#L111-L130

Fixes #138942.

Added: 
    

Modified: 
    clang/lib/Format/UnwrappedLineFormatter.cpp
    clang/unittests/Format/FormatTestSelective.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index f2ed027b2c047..ac8c0c8fd0ec0 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -986,8 +986,10 @@ class LineJoiner {
   void join(AnnotatedLine &A, const AnnotatedLine &B) {
     assert(!A.Last->Next);
     assert(!B.First->Previous);
-    if (B.Affected)
+    if (B.Affected || B.LeadingEmptyLinesAffected) {
+      assert(B.Affected || A.Last->Children.empty());
       A.Affected = true;
+    }
     A.Last->Next = B.First;
     B.First->Previous = A.Last;
     B.First->CanBreakBefore = true;

diff  --git a/clang/unittests/Format/FormatTestSelective.cpp b/clang/unittests/Format/FormatTestSelective.cpp
index 624684c7a079b..0b7ac21fd33d3 100644
--- a/clang/unittests/Format/FormatTestSelective.cpp
+++ b/clang/unittests/Format/FormatTestSelective.cpp
@@ -41,6 +41,11 @@ TEST_F(FormatTestSelective, RemovesTrailingWhitespaceOfFormattedLine) {
   EXPECT_EQ("int a;", format("int a;         ", 0, 0));
   EXPECT_EQ("int a;\n", format("int a;  \n   \n   \n ", 0, 0));
   EXPECT_EQ("int a;\nint b;    ", format("int a;  \nint b;    ", 0, 0));
+
+  EXPECT_EQ("void f() {}", format("void f() {\n"
+                                  "  \n"
+                                  "}",
+                                  11, 0));
 }
 
 TEST_F(FormatTestSelective, FormatsCorrectRegionForLeadingWhitespace) {