[clang] [clang-format] Fix an off-by-1 bug with -length option (PR #143302)

[Owen Pan via cfe-commits]

https://github.com/owenca created 
https://github.com/llvm/llvm-project/pull/143302

Also validate the argument value.

Fixes #56245

>From 30e0165a2d5c7ee8fc6b7f1edcf9322e18f4334e Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpi...@gmail.com>
Date: Sun, 8 Jun 2025 00:36:08 -0700
Subject: [PATCH] [clang-format] Fix an off-by-1 bug with -length option

Also validate the argument value.

Fixes #56245
---
 clang/test/Format/multiple-inputs-error.cpp |  2 +-
 clang/test/Format/ranges.cpp                | 13 +++++++++++--
 clang/tools/clang-format/ClangFormat.cpp    | 10 +++++++---
 3 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/clang/test/Format/multiple-inputs-error.cpp 
b/clang/test/Format/multiple-inputs-error.cpp
index 1aa9c9f3e2fad..7cb835d39f23e 100644
--- a/clang/test/Format/multiple-inputs-error.cpp
+++ b/clang/test/Format/multiple-inputs-error.cpp
@@ -1,6 +1,6 @@
 // RUN: cp %s %t-1.cpp
 // RUN: cp %s %t-2.cpp
-// RUN: not clang-format 2>&1 >/dev/null -offset=1 -length=0 %t-1.cpp %t-2.cpp 
|FileCheck %s
+// RUN: not clang-format 2>&1 >/dev/null -offset=1 -length=1 %t-1.cpp %t-2.cpp 
|FileCheck %s
 // RUN: not clang-format 2>&1 >/dev/null -lines=1:1 %t-1.cpp %t-2.cpp 
|FileCheck %s -check-prefix=CHECK-LINE
 // CHECK: error: -offset, -length and -lines can only be used for single file.
 // CHECK-LINE: error: -offset, -length and -lines can only be used for single 
file.
diff --git a/clang/test/Format/ranges.cpp b/clang/test/Format/ranges.cpp
index 66b984e037b3c..6de407e7a20e4 100644
--- a/clang/test/Format/ranges.cpp
+++ b/clang/test/Format/ranges.cpp
@@ -1,5 +1,5 @@
-// RUN: grep -Ev "// *[A-Z-]+:" %s \
-// RUN:   | clang-format -style=LLVM -offset=2 -length=0 -offset=28 -length=0 \
+// RUN: grep -Ev "// *[A-Z0-9-]+:" %s \
+// RUN:   | clang-format -style=LLVM -offset=2 -length=1 -offset=28 -length=1 
-offset=35 -length=8 \
 // RUN:   | FileCheck -strict-whitespace %s
 // CHECK: {{^int\ \*i;$}}
 int*i;
@@ -9,3 +9,12 @@ int  *  i;
 
 // CHECK: {{^int\ \*i;$}}
 int   *   i;
+
+// CHECK: int I;
+// CHECK-NEXT: int J ;
+int I ;
+int J ;
+
+// RUN: not clang-format -length=0 < %s 2>&1 \
+// RUN:   | FileCheck -strict-whitespace -check-prefix=CHECK0 %s
+// CHECK0: error: length should be at least 1
diff --git a/clang/tools/clang-format/ClangFormat.cpp 
b/clang/tools/clang-format/ClangFormat.cpp
index ad12672fa89c1..67f49c4265cd9 100644
--- a/clang/tools/clang-format/ClangFormat.cpp
+++ b/clang/tools/clang-format/ClangFormat.cpp
@@ -283,7 +283,7 @@ static bool fillRanges(MemoryBuffer *Code,
     Lengths.push_back(Sources.getFileOffset(Sources.getLocForEndOfFile(ID)) -
                       Offsets[0]);
   } else if (Offsets.size() != Lengths.size()) {
-    errs() << "error: number of -offset and -length arguments must match.\n";
+    errs() << "error: number of -offset and -length arguments must match\n";
     return true;
   }
   for (unsigned I = 0, E = Offsets.size(); I < E; ++I) {
@@ -293,12 +293,16 @@ static bool fillRanges(MemoryBuffer *Code,
       return true;
     }
     const auto Length = Lengths[I];
+    if (Length == 0) {
+      errs() << "error: length should be at least 1\n";
+      return true;
+    }
     if (Offset + Length > Code->getBufferSize()) {
       errs() << "error: invalid length " << Length << ", offset + length ("
-             << Offset + Length << ") is outside the file.\n";
+             << Offset + Length << ") is outside the file\n";
       return true;
     }
-    Ranges.push_back(tooling::Range(Offset, Length));
+    Ranges.push_back(tooling::Range(Offset, Length - 1));
   }
   return false;
 }

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