ENH: Add version comparison to if() command

Provide VERSION_LESS, VERSION_EQUAL, and VERSION_GREATER operators in
the if() command.  This simplifies component-wise comparison of version
numbers in the form "major[.minor[.patch[.tweak]]]".

Source/cmIfCommand.cxx

@@ -284,6 +284,34 @@ namespace
     reducible = 1;
   }
 
+  //=========================================================================
+  enum Op { OpLess, OpEqual, OpGreater };
+  bool HandleVersionCompare(Op op, const char* lhs_str, const char* rhs_str)
+  {
+  // Parse out up to 4 components.
+  unsigned int lhs[4] = {0,0,0,0};
+  unsigned int rhs[4] = {0,0,0,0};
+  sscanf(lhs_str, "%u.%u.%u.%u", &lhs[0], &lhs[1], &lhs[2], &lhs[3]);
+  sscanf(rhs_str, "%u.%u.%u.%u", &rhs[0], &rhs[1], &rhs[2], &rhs[3]);
+
+  // Do component-wise comparison.
+  for(unsigned int i=0; i < 4; ++i)
+    {
+    if(lhs[i] < rhs[i])
+      {
+      // lhs < rhs, so true if operation is LESS
+      return op == OpLess;
+      }
+    else if(lhs[i] > rhs[i])
+      {
+      // lhs > rhs, so true if operation is GREATER
+      return op == OpGreater;
+      }
+    }
+  // lhs == rhs, so true if operation is EQUAL
+  return op == OpEqual;
+  }
+
   //=========================================================================
   // level 0 processes parenthetical expressions
   bool HandleLevel0(std::list<std::string> &newArgs,
@@ -552,6 +580,26 @@ namespace
           reducible, arg, newArgs, argP1, argP2);
         }
 
+      if (argP1 != newArgs.end() && argP2 != newArgs.end() &&
+        (*(argP1) == "VERSION_LESS" || *(argP1) == "VERSION_GREATER" ||
+         *(argP1) == "VERSION_EQUAL"))
+        {
+        def = cmIfCommand::GetVariableOrString(arg->c_str(), makefile);
+        def2 = cmIfCommand::GetVariableOrString((argP2)->c_str(), makefile);
+        Op op = OpEqual;
+        if(*argP1 == "VERSION_LESS")
+          {
+          op = OpLess;
+          }
+        else if(*argP1 == "VERSION_GREATER")
+          {
+          op = OpGreater;
+          }
+        bool result = HandleVersionCompare(op, def, def2);
+        HandleBinaryOp(result,
+          reducible, arg, newArgs, argP1, argP2);
+        }
+
       // is file A newer than file B
       if (argP1 != newArgs.end() && argP2 != newArgs.end() &&
           *(argP1) == "IS_NEWER_THAN")

Source/cmIfCommand.h

@@ -177,6 +177,11 @@ public:
       "  if(string STREQUAL string)\n"
       "True if the given string or variable's value is lexicographically "
       "less (or greater, or equal) than the string on the right.\n"
+      "  if(version1 VERSION_LESS version2)\n"
+      "  if(version1 VERSION_EQUAL version2)\n"
+      "  if(version1 VERSION_GREATER version2)\n"
+      "Component-wise integer version number comparison (version format is "
+      "major[.minor[.patch[.tweak]]]).\n"
       "  if(DEFINED variable)\n"
       "True if the given variable is defined. It does not matter if the "
       "variable is true or false just if it has been set.";

Tests/FindPackageTest/CMakeLists.txt

@@ -145,3 +145,20 @@ IF(NOT "${Special_VERSION_MINOR}" STREQUAL "2")
   MESSAGE(SEND_ERROR
     "Package Special is minor version [${Special_VERSION_MINOR}], not [2]")
 ENDIF(NOT "${Special_VERSION_MINOR}" STREQUAL "2")
+
+# Test version number comparison.
+IF(NOT "1.2.3.4" VERSION_LESS "1.2.3.5")
+  MESSAGE(SEND_ERROR "1.2.3.4 VERSION_LESS 1.2.3.5 is not true!")
+ENDIF()
+IF(NOT "1.2" VERSION_LESS "1.10")
+  MESSAGE(SEND_ERROR "1.2 VERSION_LESS 1.10 is not true!")
+ENDIF()
+IF(NOT "1.02" VERSION_GREATER "1.1")
+  MESSAGE(SEND_ERROR "1.02 VERSION_GREATER 1.1 is not true!")
+ENDIF()
+IF("1.2.3" VERSION_GREATER "1.2.3.4")
+  MESSAGE(SEND_ERROR "1.2.3 VERSION_GREATER 1.2.3.4 is not false!")
+ENDIF()
+IF(NOT "1.2" VERSION_EQUAL "1.2.0.0")
+  MESSAGE(SEND_ERROR "1.2 VERSION_EQUAL 1.2.0.0 is not true!")
+ENDIF()