Create GLOBAL_DEPENDS_NO_CYCLES property

This global property disallows cycles in the inter-target dependency
graph even among STATIC libraries.  See issue #9444.

Source/cmComputeTargetDepends.cxx

@@ -103,6 +103,7 @@ cmComputeTargetDepends::cmComputeTargetDepends(cmGlobalGenerator* gg)
   this->GlobalGenerator = gg;
   cmake* cm = this->GlobalGenerator->GetCMakeInstance();
   this->DebugMode = cm->GetPropertyAsBool("GLOBAL_DEPENDS_DEBUG_MODE");
+  this->NoCycles = cm->GetPropertyAsBool("GLOBAL_DEPENDS_NO_CYCLES");
 }
 
 //----------------------------------------------------------------------------
@@ -344,6 +345,13 @@ cmComputeTargetDepends
       continue;
       }
 
+    // Immediately complain if no cycles are allowed at all.
+    if(this->NoCycles)
+      {
+      this->ComplainAboutBadComponent(ccg, c);
+      return false;
+      }
+
     // Make sure the component is all STATIC_LIBRARY targets.
     for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
@@ -391,8 +399,16 @@ cmComputeTargetDepends
         }
       }
     }
-  e << "At least one of these targets is not a STATIC_LIBRARY.  "
-    << "Cyclic dependencies are allowed only among static libraries.";
+  if(this->NoCycles)
+    {
+    e << "The GLOBAL_DEPENDS_NO_CYCLES global property is enabled, so "
+      << "cyclic dependencies are not allowed even among static libraries.";
+    }
+  else
+    {
+    e << "At least one of these targets is not a STATIC_LIBRARY.  "
+      << "Cyclic dependencies are allowed only among static libraries.";
+    }
   cmSystemTools::Error(e.str().c_str());
 }
 

Source/cmComputeTargetDepends.h

@@ -54,6 +54,7 @@ private:
 
   cmGlobalGenerator* GlobalGenerator;
   bool DebugMode;
+  bool NoCycles;
 
   // Collect all targets.
   std::vector<cmTarget*> Targets;

Source/cmake.cxx

@@ -3414,6 +3414,16 @@ void cmake::DefineProperties(cmake *cm)
     "at the beginning of native build system generation.  "
     "This property causes it to display details of its analysis to stderr.");
 
+  cm->DefineProperty(
+    "GLOBAL_DEPENDS_NO_CYCLES", cmProperty::GLOBAL,
+    "Disallow global target dependency graph cycles.",
+    "CMake automatically analyzes the global inter-target dependency graph "
+    "at the beginning of native build system generation.  "
+    "It reports an error if the dependency graph contains a cycle that "
+    "does not consist of all STATIC library targets.  "
+    "This property tells CMake to disallow all cycles completely, even "
+    "among static libraries.");
+
   cm->DefineProperty(
     "ALLOW_DUPLICATE_CUSTOM_TARGETS", cmProperty::GLOBAL,
     "Allow duplicate custom targets to be created.",