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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-format

Author: Eric Li (tJener)

<details>
<summary>Changes</summary>

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 if the previous token did not have children.

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

Fixes #<!-- -->138942.

---
Full diff: https://github.com/llvm/llvm-project/pull/146761.diff


2 Files Affected:

- (modified) clang/lib/Format/UnwrappedLineFormatter.cpp (+2) 
- (modified) clang/unittests/Format/FormatTestSelective.cpp (+2) 


``````````diff
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index f2ed027b2c047..d22bfc61ed736 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -988,6 +988,8 @@ class LineJoiner {
     assert(!B.First->Previous);
     if (B.Affected)
       A.Affected = true;
+    else if (B.LeadingEmptyLinesAffected && 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..3500b7d47e99d 100644
--- a/clang/unittests/Format/FormatTestSelective.cpp
+++ b/clang/unittests/Format/FormatTestSelective.cpp
@@ -41,6 +41,8 @@ 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() {}\n", format("void f() {\n  \n}\n", 11, 0));
 }
 
 TEST_F(FormatTestSelective, FormatsCorrectRegionForLeadingWhitespace) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/146761