target_link_libraries: Allow use with targets in other directories

Previously the command did not allow naming targets on the LHS that
were not created in the calling directory.  Lift this restriction to
enable more flexible use by projects.

Targets named on the RHS will need to be looked up during generation in
the scope of the call site rather than the scope of the LHS target.
Introduce an internal syntax in `[INTERFACE_]LINK_LIBRARIES` properties
to specify target names that need to be looked up in a directory other
than that containing the target on which the property is set.  Add
minimal documentation of the syntax to help users that encounter it.

Unfortunately CMake previously did allow such calls in the case that
only `INTERFACE` libraries are specified, but those libraries would be
looked up in the target's directory rather than the caller's.  Add
policy `CMP0079` to enable the new behavior with new lookup scope in a
compatible way.

Fixes: #17943

27 files changed, 77 insertions, 11 deletions

diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-NEW-stdout.txt b/Tests/RunCMake/target_link_libraries/CMP0079-iface-NEW-stdout.txt
new file mode 100644
index 0000000000..89cd806339
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-NEW-stdout.txt
@@ -0,0 +1 @@
+-- INTERFACE_LINK_LIBRARIES='foo::@<[Xx0-9A-Fa-f]+>'
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-NEW.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-iface-NEW.cmake
new file mode 100644
index 0000000000..82486c42cd
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-NEW.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0079 NEW)
+include(CMP0079-iface-common.cmake)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-OLD-stdout.txt b/Tests/RunCMake/target_link_libraries/CMP0079-iface-OLD-stdout.txt
new file mode 100644
index 0000000000..e575e16754
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-OLD-stdout.txt
@@ -0,0 +1 @@
+-- INTERFACE_LINK_LIBRARIES='foo'
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-OLD.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-iface-OLD.cmake
new file mode 100644
index 0000000000..e04a2bb53d
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-OLD.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0079 OLD)
+include(CMP0079-iface-common.cmake)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN-stderr.txt b/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN-stderr.txt
new file mode 100644
index 0000000000..6dd7d30698
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN-stderr.txt
@@ -0,0 +1,17 @@
+^CMake Warning \(dev\) at CMP0079-iface/CMakeLists.txt:[0-9]+ \(target_link_libraries\):
+  Policy CMP0079 is not set: target_link_libraries allows use with targets in
+  other directories.  Run "cmake --help-policy CMP0079" for policy details.
+  Use the cmake_policy command to set the policy and suppress this warning.
+
+  Target
+
+    top
+
+  is not created in this directory.  For compatibility with older versions of
+  CMake, link library
+
+    foo
+
+  will be looked up in the directory in which the target was created rather
+  than in this calling directory.
+This warning is for project developers.  Use -Wno-dev to suppress it.$
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN-stdout.txt b/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN-stdout.txt
new file mode 100644
index 0000000000..e575e16754
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN-stdout.txt
@@ -0,0 +1 @@
+-- INTERFACE_LINK_LIBRARIES='foo'
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN.cmake
new file mode 100644
index 0000000000..2041893c86
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-WARN.cmake
@@ -0,0 +1 @@
+include(CMP0079-iface-common.cmake)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface-common.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-iface-common.cmake
new file mode 100644
index 0000000000..3982ff264c
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface-common.cmake
@@ -0,0 +1,6 @@
+enable_language(C)
+
+add_executable(top empty.c)
+add_subdirectory(CMP0079-iface)
+get_property(libs TARGET top PROPERTY INTERFACE_LINK_LIBRARIES)
+message(STATUS "INTERFACE_LINK_LIBRARIES='${libs}'")
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-iface/CMakeLists.txt b/Tests/RunCMake/target_link_libraries/CMP0079-iface/CMakeLists.txt
new file mode 100644
index 0000000000..4b15b329bc
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-iface/CMakeLists.txt
@@ -0,0 +1 @@
+target_link_libraries(top INTERFACE foo)
diff --git a/Tests/RunCMake/target_link_libraries/SubDirTarget-result.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus-result.txt
index d00491fd7e..d00491fd7e 100644
--- a/Tests/RunCMake/target_link_libraries/SubDirTarget-result.txt
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus-result.txt
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus-stderr.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus-stderr.txt
new file mode 100644
index 0000000000..b9fe3f694f
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus-stderr.txt
@@ -0,0 +1,6 @@
+^CMake Error at CMP0079-link-NEW-bogus.cmake:[0-9]+ \(add_executable\):
+  Target "top" links to target "foo::@<0xdeadbeef>" but the target was not
+  found.  Perhaps a find_package\(\) call is missing for an IMPORTED target, or
+  an ALIAS target is missing\?
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus.cmake
new file mode 100644
index 0000000000..8622f14e7f
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-bogus.cmake
@@ -0,0 +1,6 @@
+cmake_policy(SET CMP0028 NEW)
+cmake_policy(SET CMP0079 NEW)
+enable_language(C)
+
+add_executable(top empty.c)
+set_property(TARGET top APPEND PROPERTY LINK_LIBRARIES "foo::@<0xdeadbeef>")
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-stdout.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-stdout.txt
new file mode 100644
index 0000000000..84b30bd0ab
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW-stdout.txt
@@ -0,0 +1 @@
+-- LINK_LIBRARIES='foo::@<[Xx0-9A-Fa-f]+>'
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW.cmake
new file mode 100644
index 0000000000..72e4574947
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-NEW.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0079 NEW)
+include(CMP0079-link-common.cmake)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD-result.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD-result.txt
new file mode 100644
index 0000000000..d00491fd7e
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD-stderr.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD-stderr.txt
new file mode 100644
index 0000000000..0b4c4c6830
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD-stderr.txt
@@ -0,0 +1,5 @@
+^CMake Error at CMP0079-link/CMakeLists.txt:[0-9]+ \(target_link_libraries\):
+  Attempt to add link library "foo" to target "top" which is not built in
+  this directory.
+
+  This is allowed only when policy CMP0079 is set to NEW.$
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD.cmake
new file mode 100644
index 0000000000..caa7231b71
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-OLD.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0079 OLD)
+include(CMP0079-link-common.cmake)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN-result.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN-result.txt
new file mode 100644
index 0000000000..d00491fd7e
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN-stderr.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN-stderr.txt
new file mode 100644
index 0000000000..0b4c4c6830
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN-stderr.txt
@@ -0,0 +1,5 @@
+^CMake Error at CMP0079-link/CMakeLists.txt:[0-9]+ \(target_link_libraries\):
+  Attempt to add link library "foo" to target "top" which is not built in
+  this directory.
+
+  This is allowed only when policy CMP0079 is set to NEW.$
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN.cmake
new file mode 100644
index 0000000000..e83818a9d5
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-WARN.cmake
@@ -0,0 +1 @@
+include(CMP0079-link-common.cmake)
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link-common.cmake b/Tests/RunCMake/target_link_libraries/CMP0079-link-common.cmake
new file mode 100644
index 0000000000..4f9454f0a5
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link-common.cmake
@@ -0,0 +1,6 @@
+enable_language(C)
+
+add_executable(top empty.c)
+add_subdirectory(CMP0079-link)
+get_property(libs TARGET top PROPERTY LINK_LIBRARIES)
+message(STATUS "LINK_LIBRARIES='${libs}'")
diff --git a/Tests/RunCMake/target_link_libraries/CMP0079-link/CMakeLists.txt b/Tests/RunCMake/target_link_libraries/CMP0079-link/CMakeLists.txt
new file mode 100644
index 0000000000..8b2b3c94f2
--- /dev/null
+++ b/Tests/RunCMake/target_link_libraries/CMP0079-link/CMakeLists.txt
@@ -0,0 +1 @@
+target_link_libraries(top PUBLIC foo)
diff --git a/Tests/RunCMake/target_link_libraries/CMakeLists.txt b/Tests/RunCMake/target_link_libraries/CMakeLists.txt
index 12cd3c7757..8f85fbf540 100644
--- a/Tests/RunCMake/target_link_libraries/CMakeLists.txt
+++ b/Tests/RunCMake/target_link_libraries/CMakeLists.txt
@@ -1,3 +1,3 @@
 cmake_minimum_required(VERSION 2.8.4)
 project(${RunCMake_TEST} NONE)
-include(${RunCMake_TEST}.cmake)
+include(${RunCMake_TEST}.cmake NO_POLICY_SCOPE)
diff --git a/Tests/RunCMake/target_link_libraries/RunCMakeTest.cmake b/Tests/RunCMake/target_link_libraries/RunCMakeTest.cmake
index 97b0888a7e..a041d6d4e7 100644
--- a/Tests/RunCMake/target_link_libraries/RunCMakeTest.cmake
+++ b/Tests/RunCMake/target_link_libraries/RunCMakeTest.cmake
@@ -4,11 +4,17 @@ run_cmake(CMP0023-WARN)
 run_cmake(CMP0023-NEW)
 run_cmake(CMP0023-WARN-2)
 run_cmake(CMP0023-NEW-2)
+run_cmake(CMP0079-iface-WARN)
+run_cmake(CMP0079-iface-OLD)
+run_cmake(CMP0079-iface-NEW)
+run_cmake(CMP0079-link-WARN)
+run_cmake(CMP0079-link-OLD)
+run_cmake(CMP0079-link-NEW)
+run_cmake(CMP0079-link-NEW-bogus)
 run_cmake(ImportedTarget)
 run_cmake(ImportedTargetFailure)
 run_cmake(MixedSignature)
 run_cmake(Separate-PRIVATE-LINK_PRIVATE-uses)
-run_cmake(SubDirTarget)
 run_cmake(SharedDepNotTarget)
 run_cmake(StaticPrivateDepNotExported)
 run_cmake(StaticPrivateDepNotTarget)
diff --git a/Tests/RunCMake/target_link_libraries/SubDirTarget-stderr.txt b/Tests/RunCMake/target_link_libraries/SubDirTarget-stderr.txt
deleted file mode 100644
index 5cd1f23d7b..0000000000
--- a/Tests/RunCMake/target_link_libraries/SubDirTarget-stderr.txt
+++ /dev/null
@@ -1,5 +0,0 @@
-^CMake Error at SubDirTarget.cmake:[0-9]+ \(target_link_libraries\):
-  Attempt to add link library "m" to target "subexe" which is not built in
-  this directory.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/target_link_libraries/SubDirTarget.cmake b/Tests/RunCMake/target_link_libraries/SubDirTarget.cmake
deleted file mode 100644
index 32431cecc0..0000000000
--- a/Tests/RunCMake/target_link_libraries/SubDirTarget.cmake
+++ /dev/null
@@ -1,3 +0,0 @@
-enable_language(C)
-add_subdirectory(SubDirTarget)
-target_link_libraries(subexe m)
diff --git a/Tests/RunCMake/target_link_libraries/SubDirTarget/CMakeLists.txt b/Tests/RunCMake/target_link_libraries/SubDirTarget/CMakeLists.txt
deleted file mode 100644
index b0b23809a6..0000000000
--- a/Tests/RunCMake/target_link_libraries/SubDirTarget/CMakeLists.txt
+++ /dev/null
@@ -1 +0,0 @@
-add_executable(subexe ../empty.c)