[clang] [Clang][NFC] Clarify some SourceManager related code (PR #153527)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik created https://github.com/llvm/llvm-project/pull/153527

Static analysis flagged the columns - 1 code, it was correct but the assumption was not obvious. I document the assumption w/ assertions.

While digging through related code I found getColumnNumber that looks wrong at first inspection and adding parentheses makes it clearer.

>From 6cd84865703310651f910f5f467204a354f49715 Mon Sep 17 00:00:00 2001
From: Shafik Yaghmour <shafik.yaghmour at intel.com>
Date: Wed, 13 Aug 2025 19:46:09 -0700
Subject: [PATCH] [Clang][NFC] Clarify some SourceManager related code

Static analysis flagged the columns - 1 code, it was correct but the assumption
was not obvious. I document the assumption w/ assertions.

While digging through related code I found getColumnNumber that looks wrong
at first inspection and adding parentheses makes it clearer.
---
 clang/lib/Basic/SourceManager.cpp     | 4 ++--
 clang/lib/Frontend/TextDiagnostic.cpp | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index 343c26e17236d..d8ec837f0f7b9 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -1171,14 +1171,14 @@ unsigned SourceManager::getColumnNumber(FileID FID, unsigned FilePos,
         if (Buf[FilePos - 1] == '\r' || Buf[FilePos - 1] == '\n')
           --FilePos;
       }
-      return FilePos - LineStart + 1;
+      return (FilePos - LineStart) + 1;
     }
   }
 
   unsigned LineStart = FilePos;
   while (LineStart && Buf[LineStart-1] != '\n' && Buf[LineStart-1] != '\r')
     --LineStart;
-  return FilePos-LineStart+1;
+  return (FilePos - LineStart) + 1;
 }
 
 // isInvalid - Return the result of calling loc.isInvalid(), and
diff --git a/clang/lib/Frontend/TextDiagnostic.cpp b/clang/lib/Frontend/TextDiagnostic.cpp
index ccdd59da89bd1..cb35257003441 100644
--- a/clang/lib/Frontend/TextDiagnostic.cpp
+++ b/clang/lib/Frontend/TextDiagnostic.cpp
@@ -1095,6 +1095,8 @@ prepareAndFilterRanges(const SmallVectorImpl<CharSourceRange> &Ranges,
 
     unsigned StartColumn = SM.getExpansionColumnNumber(Begin);
     unsigned EndColumn = SM.getExpansionColumnNumber(End);
+    assert(StartColumn && "StartColumn has a value of 0");
+    assert(EndColumn && "EndColumn has a value of 0");
     if (R.isTokenRange())
       EndColumn += Lexer::MeasureTokenLength(End, SM, LangOpts);