The current version/debug system has some undefined/unenforced corners.

#--- sample 1 ---
version(A){
	pragma(msg, "everytime");
}else{
	version=A;
}
#------

The "everytime" message will always be displayed.


#--- sample 2 ----
version=A;

version(A){
	version=B;
}

version(B){
	pragma(msg, "sometimes");
}
#------

#--- sample 3 ----
version(A){
	version=B;
}

version=A;

version(B){
	pragma(msg, "sometimes");
}
#------

The content of sample 3 is a reordered sample 2.
Sample 2 displays the message whereas sample 3 displays nothing.


I suggest a query-change lock mechanism to close those corners.

The compiler has to ensure that re-evaluating a conditional -
"version(A)" - will always have the same result.

#--- sample 4 ---
version(A){
	pragma(msg, "A: true");
}
version=A; // ***illegal, the status of A was changed***
#------


#--- sample 5 ---
version=A;
version(A){
	pragma(msg, "A: true");
}
version=A; // ***legal, the status of A didn't change ***
#------


#--- sample 6 ---
version=2;
version(2){
	pragma(msg, "level >= 2");
}
version=3; // ***legal***
#------
true: newLevel >= highestQuery
true: highestQuery >= current level


#--- sample 7 ---
version=1;
version(2){
	pragma(msg, "level >= 2");
}
version=3; // ***illegal***
#------
true: newLevel >= highestQuery
false: highestQuery >= currentLevel


#--- sample 8 ---
version=1;
version(2){
	pragma(msg, "level >= 2");
}
version=0; // ***illegal***
#------
false: newLevel >= highestQuery
true: highestQuery >= currentLevel


Thomas

Yeah, I was thinking that too. You're right.