Tolerate cycles in shared library link interfaces (#12647)

Since commit 183b9509 (Follow all dependencies of shared library private
dependencies, 2011-12-14) we honor LINK_INTERFACE_LIBRARIES when
following dependent shared libraries.  The link interface properties may
form a cycle if set incorrectly by a project.  Furthermore, the property
LINK_DEPENDENT_LIBRARIES may form a cycle if set incorrectly by hand
(though CMake should never generate one).  In either case, do not follow
the cycle forever when following the dependent shared library closure.
We only need to add dependency edges to the constraint graph once.

Add "LinkInterfaceLoop" test to cover this case.

3 files changed, 29 insertions, 0 deletions

diff --git a/Tests/CMakeOnly/LinkInterfaceLoop/CMakeLists.txt b/Tests/CMakeOnly/LinkInterfaceLoop/CMakeLists.txt
new file mode 100644
index 0000000000..56e449afdd
--- /dev/null
+++ b/Tests/CMakeOnly/LinkInterfaceLoop/CMakeLists.txt
@@ -0,0 +1,27 @@
+cmake_minimum_required (VERSION 2.8)
+project(LinkInterfaceLoop C)
+
+# Add a shared library that incorrectly names itself as a
+# dependency, thus forming a cycle.
+add_library(A SHARED IMPORTED)
+set_target_properties(A PROPERTIES
+  IMPORTED_LINK_DEPENDENT_LIBRARIES A
+  IMPORTED_LOCATION "${CMAKE_CURRENT_BINARY_DIR}/dirA/A"
+  )
+
+# Add a shared library that incorrectly names itself in
+# its link interface, thus forming a cycle.
+add_library(B SHARED IMPORTED)
+set_target_properties(B PROPERTIES
+  IMPORTED_LINK_INTERFACE_LIBRARIES B
+  IMPORTED_LOCATION "${CMAKE_CURRENT_BINARY_DIR}/dirB/B"
+  )
+
+# Add a shared library with an empty link interface
+# that depends on two shared libraries.
+add_library(C SHARED lib.c)
+set_property(TARGET C PROPERTY LINK_INTERFACE_LIBRARIES "")
+target_link_libraries(C B A)
+
+add_executable(main main.c)
+target_link_libraries(main C)
diff --git a/Tests/CMakeOnly/LinkInterfaceLoop/lib.c b/Tests/CMakeOnly/LinkInterfaceLoop/lib.c
new file mode 100644
index 0000000000..fede1d61f9
--- /dev/null
+++ b/Tests/CMakeOnly/LinkInterfaceLoop/lib.c
@@ -0,0 +1 @@
+int lib(void) { return 0; }
diff --git a/Tests/CMakeOnly/LinkInterfaceLoop/main.c b/Tests/CMakeOnly/LinkInterfaceLoop/main.c
new file mode 100644
index 0000000000..78f2de106c
--- /dev/null
+++ b/Tests/CMakeOnly/LinkInterfaceLoop/main.c
@@ -0,0 +1 @@
+int main(void) { return 0; }