Allow directory names containing '=' and warn if necessary (#12934)

The approach taken by commit 8704525f (Reject directory names containing
'=', 2011-01-14) was perhaps too heavy-handed for avoiding the obscure
cases when '=' in the path fails due to limitations of Make syntax.
Only two CMake tests:

  LinkDirectory
  OutOfSource

fail when the path contains '=' and they cover obscure cases.  Instead
of rejecting such paths outright just warn when the problem may occur.

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -561,6 +561,21 @@ cmLocalUnixMakefileGenerator3
     space = " ";
     }
 
+  // Warn about paths not supported by Make tools.
+  std::string::size_type pos = tgt.find_first_of("=");
+  if(pos != std::string::npos)
+    {
+    cmOStringStream m;
+    m <<
+      "Make rule for\n"
+      "  " << tgt << "\n"
+      "has '=' on left hand side.  "
+      "The make tool may not support this.";
+    cmListFileBacktrace bt;
+    this->GlobalGenerator->GetCMakeInstance()
+      ->IssueMessage(cmake::WARNING, m.str(), bt);
+    }
+
   // Mark the rule as symbolic if requested.
   if(symbolic)
     {

Source/cmake.cxx

@@ -1946,32 +1946,8 @@ int cmake::Configure()
 
 }
 
-bool cmake::RejectUnsupportedPaths(const char* desc, std::string const& path)
-{
-  // Some characters are not well-supported by native build systems.
-  std::string::size_type pos = path.find_first_of("=");
-  if(pos == std::string::npos)
-    {
-    return false;
-    }
-  cmOStringStream e;
-  e << "The path to the " << desc << " directory:\n"
-    << "  " << path << "\n"
-    << "contains unsupported character '" << path[pos] << "'.\n"
-    << "Please use a different " << desc << " directory name.";
-  cmListFileBacktrace bt;
-  this->IssueMessage(cmake::FATAL_ERROR, e.str(), bt);
-  return true;
-}
-
 int cmake::ActualConfigure()
 {
-  if(this->RejectUnsupportedPaths("source", this->cmHomeDirectory) ||
-     this->RejectUnsupportedPaths("binary", this->HomeOutputDirectory))
-    {
-    return 1;
-    }
-
   // Construct right now our path conversion table before it's too late:
   this->UpdateConversionPathTable();
   this->CleanupCommandsAndMacros();

Source/cmake.h

@@ -435,8 +435,6 @@ protected:
 
   ///! Find the full path to one of the cmake programs like ctest, cpack, etc.
   std::string FindCMakeProgram(const char* name) const;
-
-  bool RejectUnsupportedPaths(const char* desc, std::string const& path);
 private:
   cmake(const cmake&);  // Not implemented.
   void operator=(const cmake&);  // Not implemented.