Revert "build: Throw an error instead of warning for sourceless targets"

This reverts commit 651aede.

This was most certainly not acceptable.

Author: eli-schwartz

mesonbuild/build.py

@@ -760,7 +760,9 @@ def __init__(
 
         if not any([[src for src in self.sources if not is_header(src)], self.generated, self.objects,
                     self.link_whole_targets, self.structured_sources, kwargs.pop('_allow_no_sources', False)]):
-            raise MesonException(f'Build target {name} has no sources.')
+            mlog.warning(f'Build target {name} has no sources. '
+                         'This was never supposed to be allowed but did because of a bug, '
+                         'support will be removed in a future release of Meson')
         self.check_unknown_kwargs(kwargs)
         self.validate_install()
         self.check_module_linking()

test cases/common/44 pkgconfig-gen/meson.build

@@ -189,7 +189,7 @@ endtestcase
 # Make sure the -uninstalled.pc file contains both include directories.
 # See dependencies/test2.c that gets built against both simple7.pc and
 # simple7-uninstalled.pc.
-simple7 = library('simple7', 'simple7.c', include_directories: 'inc1')
+simple7 = library('simple7', include_directories: 'inc1')
 dep = declare_dependency(include_directories: 'inc2')
 install_headers('inc1/inc1.h', 'inc2/inc2.h')
 pkgg.generate(simple7, libraries: dep)

test cases/common/44 pkgconfig-gen/simple7.c

@@ -0,0 +1,7 @@
+{
+  "stdout": [
+    {
+      "line": "WARNING: Build target no sources has no sources. This was never supposed to be allowed but did because of a bug, support will be removed in a future release of Meson"
+    }
+  ]
+}

test cases/failing/136 target with no sources/test.json

@@ -4819,7 +4819,7 @@ def output_name(name, type_):
                            for_machine=MachineChoice.HOST, sources=[],
                            structured_sources=None,
                            objects=[], environment=env, compilers=env.coredata.compilers[MachineChoice.HOST],
-                           kwargs={'_allow_no_sources': True})
+                           kwargs={})
             target.process_compilers_late()
             return target.filename