Serialize CustomTargets with newlines in command.

mesonbuild/backend/ninjabackend.py

@@ -38,8 +38,11 @@ else:
     rmfile_prefix = 'rm -f {} &&'
 
 def ninja_quote(text):
-    for char in ('$', ' ', ':', '\n'):
+    for char in ('$', ' ', ':'):
         text = text.replace(char, '$' + char)
+    if '\n' in text:
+        raise MesonException('Ninja does not support newlines in rules. '
+                             'Please report this error with a test case to the Meson bug tracker.')
     return text
 
 
@@ -482,12 +485,16 @@ int dummy;
         # If the target requires capturing stdout, then use the serialized
         # executable wrapper to capture that output and save it to a file.
         #
+        # If the command line requires a newline, also use the wrapper, as
+        # ninja does not support them in its build rule syntax.
+        #
         # 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 ((mesonlib.is_windows() or mesonlib.is_cygwin()) and
+        if (target.capture or any('\n' in c for c in cmd) or
-                              self.determine_windows_extra_paths(target.command[0])):
+                ((mesonlib.is_windows() or mesonlib.is_cygwin()) and
+                 self.determine_windows_extra_paths(target.command[0]))):
             exe_data = self.serialize_executable(target.command[0], cmd[1:],
                                                  # All targets are built from the build dir
                                                  self.environment.get_build_dir(),