build: Throw an error instead of warning for sourceless targets

We might run into an assertion failure down the road, if we don't fail
here. Specifically
    project('proj')
    executable('bin', 'header.h')
will throw during the ninja generation.

Author: sp1ritCS

mesonbuild/build.py

@@ -760,9 +760,7 @@ 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)]):
-            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')
+            raise MesonException(f'Build target {name} has no sources.')
         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', include_directories: 'inc1')
+simple7 = library('simple7', 'simple7.c', 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": "test cases/failing/136 target with no sources/meson.build:3:0: ERROR: Build target no sources has no sources."
+    }
+  ]
+}

test cases/warning/8 target with no sources/meson.build renamed to test cases/failing/136 target with no sources/meson.build

@@ -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={})
+                           kwargs={'_allow_no_sources': True})
             target.process_compilers_late()
             return target.filename