Source: Avoid out-of-range inputs to std::isspace()

`isspace` takes `int` but documents that the value must be representable
by `unsigned char`, or be EOF.  Use a wrapper to cast to `unsigned char`
to avoid sign extension while converting to `int`.  This generalizes the
fix from commit 5e8c176e2a (cmExecuteProcessCommand: Cast c to unsigned
char before cast to int, 2024-01-05) to other `isspace` call sites.

This was detected by assertions in the MSVC standard library while
processing UTF-8 text.

Issue: #25561

1 files changed, 4 insertions, 1 deletions

diff --git a/Source/cmStringAlgorithms.h b/Source/cmStringAlgorithms.h
index 4a9840b..55a1e46 100644
--- a/Source/cmStringAlgorithms.h
+++ b/Source/cmStringAlgorithms.h
@@ -44,7 +44,10 @@ private:
 /** Returns true if the character @a ch is a whitespace character.  **/
 inline bool cmIsSpace(char ch)
 {
-  return ((ch & 0x80) == 0) && std::isspace(ch);
+  // isspace takes 'int' but documents that the value must be representable
+  // by 'unsigned char', or be EOF.  Cast to 'unsigned char' to avoid sign
+  // extension while converting to 'int'.
+  return std::isspace(static_cast<unsigned char>(ch));
 }
 
 /** Returns a string that has whitespace removed from the start and the end. */