"MSP" is for compiling Max/MSP externals.

The "right" thing to do is to add the symbol "PD" in the "right" place in the build system.

The expedient thing is to flip-flop "MSP" and "PD" in lines 8-10 of x_vexp.h.

Well, it seems that the proper symbols are defined later on anyway, it's just in this early phase when make depend or whatever is run that this problem occurs. As we'll never compile anything for Max anyway, I'd say that the simple fix suggested above should be all that's needed.

Of course, any source change in this header file might be gone again next time we backport it from upstream, so your suggested course of action should be more robust. But I really have no idea why the symbols aren't set at this point in the compilation, or why the make depend is done at this stage in the first place; it doesn't really seem to be needed, at least when building from scratch.

I'm not sure why the symbol isn't there yet for the early phase, either.

I'd say just submit a merge request with the "switcheroo" I suggested. If it actually breaks anything we'll end up with broken [expr] so it should be easy to test (or even see in the CI logs).

You mean this?

--- a/pd/src/x_vexp.h
+++ b/pd/src/x_vexp.h
@@ -5,9 +5,9 @@
 /* "expr" was written by Shahrokh Yadegari c. 1989. -msp */
 /* "expr~" and "fexpr~" conversion by Shahrokh Yadegari c. 1999,2000 */
 
-#define MSP
-#ifdef PD
-#undef MSP
+#define PD
+#ifdef MSP
+#undef PD
 #endif
 
 #ifdef PD

Come on, you don't need a PR for that, do you? ;-)

All right, there you go: !137 (merged). Haven't tested it yet...

Well, it gives me a warning x_vexp.h:8:0: warning: "PD" redefined now, but other than that it's looking good, so you may want to give it a whirl. Sorry, I'm too lazy to check which value PD should be #define'd as to make the warning go away, 1 maybe? Anyway, it's getting late and I have to teach courses tomorrow, so this will have to do for now.

Yeah, #define PD 1 seems to get rid of the warning, let me quickly augment that PR.

Done.