Read module list from .gitmodules

This patch mimics the behavior of qt.pro, where the module list is
extracted from the .gitmodules file and then topologically sorted
based on the modules dependencies.

This patch also introduces a small check to make sure all the required
dependencies are met and will be built.

Change-Id: Idd3df9b618805ca0b2347eac57aaa39c1bcdb3dd
Reviewed-by: Qt CMake Build Bot
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit b01225fb3257fa4c26d364c9a8fe5e19a04039e3)
Reviewed-by: Leander Beernaert <leander.beernaert@qt.io>

3 files changed, 184 insertions, 0 deletions

diff --git a/cmake/TopologicalSort.cmake b/cmake/TopologicalSort.cmake
new file mode 100644
index 00000000..b85e7749
--- /dev/null
+++ b/cmake/TopologicalSort.cmake
@@ -0,0 +1,148 @@
+##############################################################################
+# @file  TopologicalSort.cmake
+# @brief CMake implementation of topological sorting algorithm.
+#
+# Perform a reverse topological sort on the given LIST.
+#
+#   topological_sort(my_list "MY_" "_EDGES")
+#
+# LIST is the name of a variable containing a list of elements to be
+# sorted in reverse topological order. Each element in the list has a
+# set of outgoing edges (for example, those other list elements that
+# it depends on). In the resulting reverse topological ordering
+# (written back into the variable named LIST), an element will come
+# later in the list than any of the elements that can be reached by
+# following its outgoing edges and the outgoing edges of any vertices
+# they target, recursively. Thus, if the edges represent dependencies
+# on build targets, for example, the reverse topological ordering is
+# the order in which one would build those targets.
+#
+# For each element E in this list, the edges for E are contained in
+# the variable named ${PREFIX}${E}${SUFFIX}. If no such variable
+# exists, then it is assumed that there are no edges. For example, if
+# my_list contains a, b, and c, one could provide a dependency graph
+# using the following variables:
+#
+#     MY_A_EDGES     b
+#     MY_B_EDGES
+#     MY_C_EDGES     a b
+#
+#  With the involcation of topological_sort shown above and these
+#  variables, the resulting reverse topological ordering will be b, a, c.
+#
+# @verbatim
+##############################################################################
+# Modified from Boost Utilities
+#
+# Copyright 2010 Kitware, Inc.
+##############################################################################
+# Copyright 2007 Douglas Gregor <doug.gregor@gmail.com>
+# Copyright 2007 Troy Straszheim
+#
+# Distributed under the Boost Software License, Version 1.0.
+##############################################################################
+# Boost Software License - Version 1.0 - August 17th, 2003
+#
+# Permission is hereby granted, free of charge, to any person or organization
+# obtaining a copy of the software and accompanying documentation covered by
+# this license (the "Software") to use, reproduce, display, distribute,
+# execute, and transmit the Software, and to prepare derivative works of the
+# Software, and to permit third-parties to whom the Software is furnished to
+# do so, all subject to the following:
+#
+# The copyright notices in the Software and this entire statement, including
+# the above license grant, this restriction and the following disclaimer,
+# must be included in all copies of the Software, in whole or in part, and
+# all derivative works of the Software, unless such copies or derivative
+# works are solely in the form of machine-executable object code generated by
+# a source language processor.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+# SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+# FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+# ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+# DEALINGS IN THE SOFTWARE.
+##############################################################################
+# @endverbatim
+#
+# @ingroup CMakeUtilities
+##############################################################################
+
+function(topological_sort LIST PREFIX SUFFIX)
+  # Clear the stack and output variable
+  set(VERTICES "${${LIST}}")
+  set(STACK)
+  set(${LIST})
+
+  # Loop over all of the vertices, starting the topological sort from
+  # each one.
+  foreach(VERTEX ${VERTICES})
+
+    # If we haven't already processed this vertex, start a depth-first
+    # search from where.
+    if (NOT FOUND_${VERTEX})
+      # Push this vertex onto the stack with all of its outgoing edges
+      string(REPLACE ";" " " NEW_ELEMENT
+        "${VERTEX};${${PREFIX}${VERTEX}${SUFFIX}}")
+      list(APPEND STACK ${NEW_ELEMENT})
+
+      # We've now seen this vertex
+      set(FOUND_${VERTEX} TRUE)
+
+      # While the depth-first search stack is not empty
+      list(LENGTH STACK STACK_LENGTH)
+      while(STACK_LENGTH GREATER 0)
+        # Remove the vertex and its remaining out-edges from the top
+        # of the stack
+        list(GET STACK -1 OUT_EDGES)
+        list(REMOVE_AT STACK -1)
+
+        # Get the source vertex and the list of out-edges
+        separate_arguments(OUT_EDGES)
+        list(GET OUT_EDGES 0 SOURCE)
+        list(REMOVE_AT OUT_EDGES 0)
+
+        # While there are still out-edges remaining
+        list(LENGTH OUT_EDGES OUT_DEGREE)
+        while (OUT_DEGREE GREATER 0)
+          # Pull off the first outgoing edge
+          list(GET OUT_EDGES 0 TARGET)
+          list(REMOVE_AT OUT_EDGES 0)
+
+          if (NOT FOUND_${TARGET})
+            # We have not seen the target before, so we will traverse
+            # its outgoing edges before coming back to our
+            # source. This is the key to the depth-first traversal.
+
+            # We've now seen this vertex
+            set(FOUND_${TARGET} TRUE)
+
+            # Push the remaining edges for the current vertex onto the
+            # stack
+            string(REPLACE ";" " " NEW_ELEMENT
+              "${SOURCE};${OUT_EDGES}")
+            list(APPEND STACK ${NEW_ELEMENT})
+
+            # Setup the new source and outgoing edges
+            set(SOURCE ${TARGET})
+            set(OUT_EDGES
+              ${${PREFIX}${SOURCE}${SUFFIX}})
+          endif(NOT FOUND_${TARGET})
+
+          list(LENGTH OUT_EDGES OUT_DEGREE)
+        endwhile (OUT_DEGREE GREATER 0)
+
+        # We have finished all of the outgoing edges for
+        # SOURCE; add it to the resulting list.
+        list(APPEND ${LIST} ${SOURCE})
+
+        # Check the length of the stack
+        list(LENGTH STACK STACK_LENGTH)
+      endwhile(STACK_LENGTH GREATER 0)
+    endif (NOT FOUND_${VERTEX})
+  endforeach(VERTEX)
+
+  set(${LIST} ${${LIST}} PARENT_SCOPE)
+endfunction(topological_sort)
diff --git a/cmake/TopologicalSort_LICENSE.txt b/cmake/TopologicalSort_LICENSE.txt
new file mode 100644
index 00000000..36b7cd93
--- /dev/null
+++ b/cmake/TopologicalSort_LICENSE.txt
@@ -0,0 +1,23 @@
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/cmake/qt_attribution.json b/cmake/qt_attribution.json
new file mode 100644
index 00000000..0699021c
--- /dev/null
+++ b/cmake/qt_attribution.json
@@ -0,0 +1,13 @@
+{
+    "Id": "cmake_topological_sort",
+    "Name": "CMake Topological Sort",
+    "QDocModule": "qt",
+    "QtUsage": "Used in the CMake super build project file",
+    "Files": TopologicalSort.cmake",
+
+    "Description": "CMake implementation of the topological sort algorithm",
+    "License": "Boost Software License - Version 1.0",
+    "LicenseFile": "TopologicalSort_LICENSE.txt",
+    "Copyright": "Copyright 2010 Kitware, Inc."
+}
+