[clang] [clang-format] Fix crashes when the macro expansion is empty (PR #119428)

[via cfe-commits]

https://github.com/amane-ame updated https://github.com/llvm/llvm-project/pull/119428

>From 3a4c1a924faef3a7a09126694fcb943bd7083451 Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Wed, 11 Dec 2024 02:13:43 +0800
Subject: [PATCH 1/3] Fix crashes when the macro expansion is empty

---
 clang/lib/Format/MacroExpander.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang/lib/Format/MacroExpander.cpp b/clang/lib/Format/MacroExpander.cpp
index fd2a16894d643d..ed9e51dfbfef1f 100644
--- a/clang/lib/Format/MacroExpander.cpp
+++ b/clang/lib/Format/MacroExpander.cpp
@@ -233,6 +233,10 @@ MacroExpander::expand(FormatToken *ID,
   if (Result.size() > 1) {
     ++Result[0]->MacroCtx->StartOfExpansion;
     ++Result[Result.size() - 2]->MacroCtx->EndOfExpansion;
+  } else {
+    // If the macro expansion is empty, mark the start and end
+    Result[0]->MacroCtx->StartOfExpansion = 1;
+    Result[0]->MacroCtx->EndOfExpansion = 1;
   }
   return Result;
 }

>From 8bf68f87b897bab9da9464d594082be5012afdb1 Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Sun, 15 Dec 2024 15:15:17 +0800
Subject: [PATCH 2/3] [clang-format] Add a testcase for empty macro

---
 clang/test/Format/empty-macro.cpp | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 clang/test/Format/empty-macro.cpp

diff --git a/clang/test/Format/empty-macro.cpp b/clang/test/Format/empty-macro.cpp
new file mode 100644
index 00000000000000..81b255219b0c2b
--- /dev/null
+++ b/clang/test/Format/empty-macro.cpp
@@ -0,0 +1,5 @@
+// RUN: grep -Ev "// *[A-Z-]+:" %s | clang-format -style="{Macros: [A(x)=x]}" \
+// RUN:   | FileCheck -strict-whitespace %s
+
+// CHECK: A()
+A()

>From 1e79973ed4ea56c66f8b7eb1db9d00784edac7f0 Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Mon, 16 Dec 2024 14:25:39 +0800
Subject: [PATCH 3/3] [clang-format] Move the testcase to unittest

---
 clang/test/Format/empty-macro.cpp                    |  5 -----
 .../unittests/Format/MacroCallReconstructorTest.cpp  | 12 ++++++++++++
 2 files changed, 12 insertions(+), 5 deletions(-)
 delete mode 100644 clang/test/Format/empty-macro.cpp

diff --git a/clang/test/Format/empty-macro.cpp b/clang/test/Format/empty-macro.cpp
deleted file mode 100644
index 81b255219b0c2b..00000000000000
--- a/clang/test/Format/empty-macro.cpp
+++ /dev/null
@@ -1,5 +0,0 @@
-// RUN: grep -Ev "// *[A-Z-]+:" %s | clang-format -style="{Macros: [A(x)=x]}" \
-// RUN:   | FileCheck -strict-whitespace %s
-
-// CHECK: A()
-A()
diff --git a/clang/unittests/Format/MacroCallReconstructorTest.cpp b/clang/unittests/Format/MacroCallReconstructorTest.cpp
index b4ee8d0e37efa8..222e689f861a2b 100644
--- a/clang/unittests/Format/MacroCallReconstructorTest.cpp
+++ b/clang/unittests/Format/MacroCallReconstructorTest.cpp
@@ -217,6 +217,18 @@ TEST_F(MacroCallReconstructorTest, Identifier) {
   EXPECT_THAT(std::move(Unexp).takeResult(), matchesLine(line(U.consume("X"))));
 }
 
+TEST_F(MacroCallReconstructorTest, EmptyExpansion) {
+  auto Macros = createExpander({"A(x)=y"});
+  Expansion Exp(Lex, *Macros);
+  TokenList Call = Exp.expand("A()");
+
+  MacroCallReconstructor Unexp(0, Exp.getUnexpanded());
+  Unexp.addLine(line(Exp.getTokens()));
+  EXPECT_TRUE(Unexp.finished());
+  Matcher U(Call, Lex);
+  EXPECT_THAT(std::move(Unexp).takeResult(), matchesLine(line(U.consume("A()"))));
+}
+
 TEST_F(MacroCallReconstructorTest, NestedLineWithinCall) {
   auto Macros = createExpander({"C(a)=class X { a; };"});
   Expansion Exp(Lex, *Macros);