Move discussion of dependency licensing to Sphinx docs.

- Also enable EIGENSPARSE option by default as LGPL licensing
  implications are less severe that SuiteSparse’s GPL implications which
  is enabled by default.

Change-Id: Ic7e4fef5cef614d5ce719eeefcc35bf4b63b8dac

CMakeLists.txt

@@ -107,14 +107,8 @@ option(OPENMP "Enable threaded solving in Ceres (requires OpenMP)" ON)
 # Multithreading using TBB
 option(TBB "Enable threaded solving in Ceres with TBB (requires TBB and C++11)" OFF)
 # Enable the use of Eigen as a sparse linear algebra library for
-# solving the nonlinear least squares problems. Enabling this
-# option will result in an LGPL licensed version of Ceres Solver
-# as the Simplicial Cholesky factorization in Eigen is licensed under the LGPL.
-# This does not affect the covariance estimation algorithm, as it
-# depends on the sparse QR factorization algorithm, which is licensed
-# under the MPL.
-OPTION(EIGENSPARSE
-  "Enable Eigen as a sparse linear algebra library, WARNING: results in an LGPL licensed Ceres." OFF)
+# solving the nonlinear least squares problems.
+option(EIGENSPARSE "Enable Eigen as a sparse linear algebra library." ON)
 if (NOT MSVC)
   # Ceres does not use C++11 internally, however it does use shared_ptr
   # (required) and unordered_map (if available), both of which were present in
@@ -213,35 +207,23 @@ if (EIGEN_FOUND)
       "that Eigen/SparseCore be available, detected version of Eigen is: "
       "${EIGEN_VERSION}")
   endif (EIGEN_VERSION VERSION_LESS 3.1.0)
-
   message("-- Found Eigen version ${EIGEN_VERSION}: ${EIGEN_INCLUDE_DIRS}")
-  # Ensure that only MPL2 licensed code is part of the default build.
-  message("")
-  message("   ===============================================================")
   if (EIGENSPARSE)
+    message("-- Enabling use of Eigen as a sparse linear algebra library.")
     list(APPEND CERES_COMPILE_OPTIONS CERES_USE_EIGEN_SPARSE)
-    message("   Enabling the use of Eigen as a sparse linear algebra library ")
-    message("   for solving the nonlinear least squares problems. Enabling ")
-    message("   this option results in an LGPL licensed version of ")
-    message("   Ceres Solver as the Simplicial Cholesky factorization in Eigen")
-    message("   is licensed under the LGPL. ")
-
     if (EIGEN_VERSION VERSION_LESS 3.2.2)
       message("   WARNING:")
       message("")
-      message("   Your version of Eigen is older than version 3.2.2.")
-      message("   The performance of SPARSE_NORMAL_CHOLESKY and SPARSE_SCHUR")
-      message("   linear solvers will suffer. ")
+      message("   Your version of Eigen (${EIGEN_VERSION}) is older than ")
+      message("   version 3.2.2.  The performance of SPARSE_NORMAL_CHOLESKY ")
+      message("   and SPARSE_SCHUR linear solvers will suffer.")
     endif (EIGEN_VERSION VERSION_LESS 3.2.2)
-
   else (EIGENSPARSE)
-    message("   Disabling the use of Eigen as a sparse linear algebra library.")
+    message("-- Disabling use of Eigen as a sparse linear algebra library.")
     message("   This does not affect the covariance estimation algorithm ")
     message("   which can still use the EIGEN_SPARSE_QR algorithm.")
     add_definitions(-DEIGEN_MPL2_ONLY)
   endif (EIGENSPARSE)
-    message("   ===============================================================")
-    message("")
 endif (EIGEN_FOUND)
 
 if (LAPACK)

docs/source/installation.rst

@@ -566,6 +566,8 @@ defaults if you know what you are doing.
  ``CMake`` GUI.  If they are not present in the *Standard View*,
  toggle to the *Advanced View* with ``<t>``.
 
+.. _options-controlling-ceres-configuration:
+
 Options controlling Ceres configuration
 ---------------------------------------
 
@@ -582,20 +584,32 @@ Options controlling Ceres configuration
    ``SuiteSparse`` if it and all of its dependencies are present. Turn
    this ``OFF`` to build Ceres without ``SuiteSparse``.
 
+   .. NOTE::
+
+      SuiteSparse is licensed under a mixture of GPL/LGPL/Commercial
+      terms.  Ceres requires some components that are only licensed under
+      GPL/Commercial terms.
+
 #. ``CXSPARSE [Default: ON]``: By default, Ceres will link to
    ``CXSparse`` if all its dependencies are present. Turn this ``OFF``
    to build Ceres without ``CXSparse``.
 
+   .. NOTE::
+
+      CXSparse is licensed under the LGPL.
+
 #. ``EIGENSPARSE [Default: OFF]``: By default, Ceres will not use
-   Eigen's sparse Cholesky factorization. The is because this part of
-   the code is licensed under the ``LGPL`` and since ``Eigen`` is a
-   header only library, including this code will result in an ``LGPL``
-   licensed version of Ceres.
+   Eigen's sparse Cholesky factorization.
 
    .. NOTE::
 
       For good performance, use Eigen version 3.2.2 or later.
 
+   .. NOTE::
+
+      Unlike the rest of Eigen (>= 3.1.1 MPL2, < 3.1.1 LGPL), Eigen's sparse
+      Cholesky factorization is (still) licensed under the LGPL.
+
 #. ``GFLAGS [Default: ON]``: Turn this ``OFF`` to build Ceres without
    ``gflags``. This will also prevent some of the example code from
    building.
@@ -618,6 +632,12 @@ Options controlling Ceres configuration
 #. ``TBB [Default: OFF]``: An alternative to ``OpenMP`` threading library that
    requires C++11. This option is mutually exclusive to ``OpenMP``.
 
+   .. NOTE::
+
+      Up to and including version 4.4, TBB was licensed under
+      GPL/Commercial terms.  From 2017.x versions onwards, TBB is licensed under
+      the Apache 2.0 license (and commerical terms).
+
 #. ``CXX11 [Default: OFF]`` *Non-MSVC compilers only*.
 
    Although Ceres does not currently require C++11, it does use

docs/source/license.rst

@@ -2,6 +2,14 @@
 License
 =======
 
+.. NOTE::
+
+   This page refers only to the license for Ceres itself, independent of its
+   optional dependencies which are separately licensed and which can affect
+   the resulting license of Ceres if built with them enabled.  See
+   :ref:`options-controlling-ceres-configuration` for an overview of these
+   implications.
+
 Ceres Solver is licensed under the New BSD license, whose terms are as follows.
 
 Copyright 2016 Google Inc. All rights reserved.