Fix #15117 (MSBuild arithmetic intrinsics: signed overflow UB in Add/Subtract/Multiply) (cppcheck-opensource#8938)

The $([MSBuild]::Add/Subtract/Multiply) intrinsics in
applyMSBuildStaticFunction computed a+b, a-b and a*b directly on long
long operands from the project file, so values like
$([MSBuild]::Add(9223372036854775807, 1)) were signed-overflow UB
(reported by -fsanitize=signed-integer-overflow).

MSBuild evaluates these in .NET's unchecked context, so on overflow the
result wraps. The arithmetic is now done on unsigned long long and cast
back, which gives the same two's complement result without UB.
Divide/Modulo of LLONG_MIN by -1 throw OverflowException in .NET, so
those return the empty string with a debug message, the same as the
existing division-by-zero handling.

Regression tests added to testMSBuildStaticFunctions.

Author: Nussu06

lib/importproject.cpp

@@ -27,6 +27,7 @@
 
 #include <algorithm>
 #include <cctype>
+#include <climits>
 #include <cmath>
 #include <cstdlib>
 #include <cstring>
@@ -848,6 +849,22 @@ static std::string safeFormat(const char *fmt, Args... args) {
 #pragma clang diagnostic pop
 #endif
 
+// MSBuild evaluates the [MSBuild]::Add/Subtract/Multiply intrinsics in .NET's
+// default unchecked context, so on overflow the result wraps (two's complement).
+// Do the arithmetic on unsigned operands to get the same result without
+// signed-overflow UB.
+static long long wrapAdd(long long a, long long b) {
+    return static_cast<long long>(static_cast<unsigned long long>(a) + static_cast<unsigned long long>(b));
+}
+
+static long long wrapSub(long long a, long long b) {
+    return static_cast<long long>(static_cast<unsigned long long>(a) - static_cast<unsigned long long>(b));
+}
+
+static long long wrapMul(long long a, long long b) {
+    return static_cast<long long>(static_cast<unsigned long long>(a) * static_cast<unsigned long long>(b));
+}
+
 // Evaluate a $([ClassName]::Method(args)) static property function.
 // Returns an empty string for unknown or unimplementable functions rather
 // than throwing, so import can continue gracefully.
@@ -894,23 +911,31 @@ std::string ImportProject::applyMSBuildStaticFunction(const std::string &classNa
             long long a = 0, b = 0;
             if (toInt(args[0], a) && toInt(args[1], b)) {
                 if (caseInsensitiveStringCompare(member, "Add") == 0)
-                    return std::to_string(a + b);
+                    return std::to_string(wrapAdd(a, b));
                 if (caseInsensitiveStringCompare(member, "Subtract") == 0)
-                    return std::to_string(a - b);
+                    return std::to_string(wrapSub(a, b));
                 if (caseInsensitiveStringCompare(member, "Multiply") == 0)
-                    return std::to_string(a * b);
+                    return std::to_string(wrapMul(a, b));
                 if (caseInsensitiveStringCompare(member, "Divide") == 0) {
                     if (b == 0) {
                         addDebug("MSBuild::Divide: division by zero");
                         return std::string();
                     }
+                    if (a == LLONG_MIN && b == -1) {
+                        addDebug("MSBuild::Divide: integer overflow");
+                        return std::string();
+                    }
                     return std::to_string(a / b);
                 }
                 if (caseInsensitiveStringCompare(member, "Modulo") == 0) {
                     if (b == 0) {
                         addDebug("MSBuild::Modulo: division by zero");
                         return std::string();
                     }
+                    if (a == LLONG_MIN && b == -1) {
+                        addDebug("MSBuild::Modulo: integer overflow");
+                        return std::string();
+                    }
                     return std::to_string(a % b);
                 }
             }

test/testimportproject.cpp

@@ -1211,6 +1211,14 @@ class TestImportProject : public TestFixture {
         ASSERT_EQUALS("3", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Divide(9, 3))"));
         ASSERT_EQUALS("2", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Modulo(5, 3))"));
 
+        // Overflow wraps around like MSBuild (.NET unchecked arithmetic).
+        ASSERT_EQUALS("-9223372036854775808", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Add(9223372036854775807, 1))"));
+        ASSERT_EQUALS("9223372036854775807", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Subtract(-9223372036854775808, 1))"));
+        ASSERT_EQUALS("7766279611452241921", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Multiply(9999999999, 9999999999))"));
+        // .NET throws OverflowException for LLONG_MIN / -1 and LLONG_MIN % -1.
+        ASSERT_EQUALS("", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Divide(-9223372036854775808, -1))"));
+        ASSERT_EQUALS("", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Modulo(-9223372036854775808, -1))"));
+
         // --- $([MSBuild]::...) path helpers ---
         ASSERT_EQUALS("foo/", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::EnsureTrailingSlash('foo'))"));
         ASSERT_EQUALS("foo/", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::EnsureTrailingSlash('foo/'))"));