custom target: Consider all build depends while serializing

Currently, we only consider the build depends of the Executable being
run when serializing custom targets. However, this is not always
sufficient, for example if the executable loads modules at runtime or if
the executable is actually a python script that loads a built module.

For these cases, we need to set PATH on Windows correctly or the custom
target will fail to run at build time complaining about missing DLLs.

4 files changed, 52 insertions, 17 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index d613f5019..3e12c89fe 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -238,8 +238,14 @@ class Backend:
         return obj_list
 
     def serialize_executable(self, exe, cmd_args, workdir, env={},
-                             capture=None):
+                             extra_paths=None, capture=None):
         import hashlib
+        if extra_paths is None:
+            # The callee didn't check if we needed extra paths, so check it here
+            if mesonlib.is_windows() or mesonlib.is_cygwin():
+                extra_paths = self.determine_windows_extra_paths(exe, [])
+            else:
+                extra_paths = []
         # Can't just use exe.name here; it will likely be run more than once
         if isinstance(exe, (dependencies.ExternalProgram,
                             build.BuildTarget, build.CustomTarget)):
@@ -272,10 +278,6 @@ class Backend:
                 exe_wrapper = self.environment.cross_info.config['binaries'].get('exe_wrapper', None)
             else:
                 exe_wrapper = None
-            if mesonlib.is_windows() or mesonlib.is_cygwin():
-                extra_paths = self.determine_windows_extra_paths(exe)
-            else:
-                extra_paths = []
             es = ExecutableSerialisation(basename, exe_cmd, cmd_args, env,
                                          is_cross_built, exe_wrapper, workdir,
                                          extra_paths, capture)
@@ -529,23 +531,27 @@ class Backend:
             args.append(d_arg)
         return args
 
-    def determine_windows_extra_paths(self, target):
+    def determine_windows_extra_paths(self, target, extra_bdeps):
         '''On Windows there is no such thing as an rpath.
         We must determine all locations of DLLs that this exe
         links to and return them so they can be used in unit
         tests.'''
-        if not isinstance(target, build.Executable):
-            return []
-        prospectives = target.get_transitive_link_deps()
         result = []
+        prospectives = []
+        if isinstance(target, build.Executable):
+            prospectives = target.get_transitive_link_deps()
+            # External deps
+            for deppath in self.rpaths_for_bundled_shared_libraries(target):
+                result.append(os.path.normpath(os.path.join(self.environment.get_build_dir(), deppath)))
+        for bdep in extra_bdeps:
+            prospectives += bdep.get_transitive_link_deps()
+        # Internal deps
         for ld in prospectives:
             if ld == '' or ld == '.':
                 continue
             dirseg = os.path.join(self.environment.get_build_dir(), self.get_target_dir(ld))
             if dirseg not in result:
                 result.append(dirseg)
-        for deppath in self.rpaths_for_bundled_shared_libraries(target):
-            result.append(os.path.normpath(os.path.join(self.environment.get_build_dir(), deppath)))
         return result
 
     def write_benchmark_file(self, datafile):
@@ -576,7 +582,7 @@ class Backend:
             else:
                 exe_wrapper = None
             if mesonlib.is_windows() or mesonlib.is_cygwin():
-                extra_paths = self.determine_windows_extra_paths(exe)
+                extra_paths = self.determine_windows_extra_paths(exe, [])
             else:
                 extra_paths = []
             cmd_args = []
diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index bcda603ed..e35a391dc 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -504,22 +504,30 @@ int dummy;
             # Add a dependency on all the outputs of this target
             for output in d.get_outputs():
                 elem.add_dep(os.path.join(self.get_target_dir(d), output))
+        serialize = False
+        extra_paths = []
         # If the target requires capturing stdout, then use the serialized
         # executable wrapper to capture that output and save it to a file.
-        #
+        if target.capture:
+            serialize = True
         # If the command line requires a newline, also use the wrapper, as
         # ninja does not support them in its build rule syntax.
-        #
+        if any('\n' in c for c in cmd):
+            serialize = True
         # Windows doesn't have -rpath, so for EXEs that need DLLs built within
         # the project, we need to set PATH so the DLLs are found. We use
         # a serialized executable wrapper for that and check if the
         # CustomTarget command needs extra paths first.
-        if (target.capture or any('\n' in c for c in cmd) or
-                ((mesonlib.is_windows() or mesonlib.is_cygwin()) and
-                 self.determine_windows_extra_paths(target.command[0]))):
+        if mesonlib.is_windows() or mesonlib.is_cygwin():
+            extra_bdeps = target.get_transitive_build_target_deps()
+            extra_paths = self.determine_windows_extra_paths(target.command[0], extra_bdeps)
+            if extra_paths:
+                serialize = True
+        if serialize:
             exe_data = self.serialize_executable(target.command[0], cmd[1:],
                                                  # All targets are built from the build dir
                                                  self.environment.get_build_dir(),
+                                                 extra_paths=extra_paths,
                                                  capture=ofilenames[0] if target.capture else None)
             cmd = self.environment.get_build_command() + ['--internal', 'exe', exe_data]
             cmd_type = 'meson_exe.py custom'
diff --git a/mesonbuild/backend/vs2010backend.py b/mesonbuild/backend/vs2010backend.py
index ea02580c0..e872a0474 100644
--- a/mesonbuild/backend/vs2010backend.py
+++ b/mesonbuild/backend/vs2010backend.py
@@ -429,9 +429,12 @@ class Vs2010Backend(backends.Backend):
         # Always use a wrapper because MSBuild eats random characters when
         # there are many arguments.
         tdir_abs = os.path.join(self.environment.get_build_dir(), self.get_target_dir(target))
+        extra_bdeps = target.get_transitive_build_target_deps()
+        extra_paths = self.determine_windows_extra_paths(target.command[0], extra_bdeps)
         exe_data = self.serialize_executable(target.command[0], cmd[1:],
                                              # All targets run from the target dir
                                              tdir_abs,
+                                             extra_paths=extra_paths,
                                              capture=ofilenames[0] if target.capture else None)
         wrapper_cmd = self.environment.get_build_command() + ['--internal', 'exe', exe_data]
         ET.SubElement(customstep, 'Command').text = ' '.join(self.quote_arguments(wrapper_cmd))
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 8eb95dc13..7757300c5 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -1549,6 +1549,24 @@ class CustomTarget(Target):
                 deps.append(c)
         return deps
 
+    def get_transitive_build_target_deps(self):
+        '''
+        Recursively fetch the build targets that this custom target depends on,
+        whether through `command:`, `depends:`, or `sources:` The recursion is
+        only performed on custom targets.
+        This is useful for setting PATH on Windows for finding required DLLs.
+        F.ex, if you have a python script that loads a C module that links to
+        other DLLs in your project.
+        '''
+        bdeps = set()
+        deps = self.get_target_dependencies()
+        for d in deps:
+            if isinstance(d, BuildTarget):
+                bdeps.add(d)
+            elif isinstance(d, CustomTarget):
+                bdeps.update(d.get_transitive_build_target_deps())
+        return bdeps
+
     def flatten_command(self, cmd):
         cmd = listify(cmd, unholder=True)
         final_cmd = []