cmake module: Better warnings and error messages in some cases.

1 files changed, 7 insertions, 0 deletions

diff --git a/mesonbuild/cmake/traceparser.py b/mesonbuild/cmake/traceparser.py
index 4dc09ff..e841c7a 100644
--- a/mesonbuild/cmake/traceparser.py
+++ b/mesonbuild/cmake/traceparser.py
@@ -231,7 +231,14 @@ class CMakeTraceParser:
 
         for ctgt in self.custom_targets:
             ctgt.outputs = pathlist_gen(ctgt._outputs_str)
+            temp = ctgt.command
             ctgt.command = [strlist_gen(x) for x in ctgt.command]
+            for command, src in zip(ctgt.command, temp):
+                if command[0] == "":
+                    raise CMakeException(
+                        "We have a problem: We would like to generate a recipe for a target that should be generated by the custom command %s\nThe problem is that the executable that should be called, here: '%s', is a variable that evaluates to an empty string. An empty string is not a valid path to an executable so ninja will not be able to call it."
+                        % (repr(src), src[0])
+                    )
             ctgt.working_dir = Path(parse_generator_expressions(str(ctgt.working_dir), self)) if ctgt.working_dir is not None else None
 
         # Postprocess