Astgen: more unreachable checks

[nektro]

Also fixes #9630

[ifreund]

Why have only some uses of expr() been replaced with reachableExpr()? It seems to me that every nearly every usage of expr() needs to check if the expr() is noreturn. I wonder if renaming expr() to exprMaybeNoReturn() and reachableExpr() to expr() would be the best way forward.

Note that the current reachableExpr() also should be updated to use GenZir.endsWithNoReturn().

[ifreund]

On further investigation, I think the only place where we wouldn't be able to use the semantics of the current reachableExpr() would be in unusedResultExpr().

[ifreund]

Though now I've remembered about #3257 and wonder if we're on the totally wrong path here...

[ifreund]

Note: if we apply these checks wherever technically possible this would make the following pattern fail to compile:

pub const ensureCapacity = @compileError("deprecated for ensureUnusedCapacity and ...");

however, this could be worked around by wrapping the @compileError() call in a function or block:

pub const ensureCapacity = {
    @compileError("deprecated...");
};
// or
pub fn ensureCapacity(self: *Self, new_capacity: usize) !void {
    @compileError("deprecated...");
}

Applying these checks wherever possible would certainly be the most consistent approach IMO, and I don't find the workarounds too unpalatable. This feels quite arbitrary though...

[andrewrk]

what happened to this nice error note?

[andrewrk]

If someone wants to pick this back up:

• use the reachableExpr function that I have provided, for example in c42763f
• add test coverage for each one. yes, each one. again, example is in c42763f