Eclipse: Add property to include additional contents in .cproject file

Similar to ECLIPSE_EXTRA_NATURES which can be used to add a third party
nature to the .project, this property offers the possibility to inject
third party contents into the .cproject.

An example of where this is useful is MCUXpresso. This is an IDE based
on Eclipse. Compiling through CMake generated Eclipse projects works
fine by using a custom toolchain. However, in order to be able to debug
using such a project, an extra storageModule specific to the target
board is needed in the cproject.

Help/manual/cmake-properties.7.rst

@@ -40,6 +40,7 @@ Properties of Global Scope
    /prop_gbl/JOB_POOLS
    /prop_gbl/PREDEFINED_TARGETS_FOLDER
    /prop_gbl/ECLIPSE_EXTRA_NATURES
+   /prop_gbl/ECLIPSE_EXTRA_CPROJECT_CONTENTS
    /prop_gbl/REPORT_UNDEFINED_PROPERTIES
    /prop_gbl/RULE_LAUNCH_COMPILE
    /prop_gbl/RULE_LAUNCH_CUSTOM

Help/prop_gbl/ECLIPSE_EXTRA_CPROJECT_CONTENTS.rst

@@ -0,0 +1,12 @@
+ECLIPSE_EXTRA_CPROJECT_CONTENTS
+-------------------------------
+
+Additional contents to be inserted into the generated Eclipse cproject file.
+
+The cproject file defines the CDT specific information. Some third party IDE's
+are based on Eclipse with the addition of other information specific to that IDE.
+Through this property, it is possible to add this additional contents to
+the generated project.
+It is expected to contain valid XML.
+
+Also see the :prop_gbl:`ECLIPSE_EXTRA_NATURES` property.

Help/prop_gbl/ECLIPSE_EXTRA_NATURES.rst

@@ -6,3 +6,5 @@ List of natures to add to the generated Eclipse project file.
 Eclipse projects specify language plugins by using natures. This property
 should be set to the unique identifier for a nature (which looks like a Java
 package name).
+
+Also see the :prop_gbl:`ECLIPSE_EXTRA_CPROJECT_CONTENTS` property.

Source/cmExtraEclipseCDT4Generator.cxx

@@ -1001,6 +1001,13 @@ void cmExtraEclipseCDT4Generator::CreateCProjectFile() const
   xml.EndElement(); // project
 
   xml.EndElement(); // storageModule
+
+  // Append additional cproject contents without applying any XML formatting
+  if (const char* extraCProjectContents =
+        mf->GetState()->GetGlobalProperty("ECLIPSE_EXTRA_CPROJECT_CONTENTS")) {
+    fout << extraCProjectContents;
+  }
+
   xml.EndElement(); // cproject
 }