lib/systems/parse.nix: mkSkeletonFromList: improve readability

The main purpose of this PR is to make the basis for
`mkSkeletonFromList`'s decision between `cpu-kernel-libcabi` vs
`cpu-vendor-os` clear, without changing its behavior.  The existing
code obscures this decision behind a sequence of prioritized matches
(i.e. `if-then`) which jump around between different coordinates.

Two side benefits of this PR:

1. It makes the root cause of #165836 obvious: we are missing a case
   for `cpu-vendor-libcabi`.  This is why nixpkgs stumbles over
   `*-none-*`.

2. It illuminates some very weird corner cases in the existing
   logic, like `*-${vendor}-ghcjs` overriding the `vendor` field,
   and `mingw32` being transformed into `windows` in some cases.

Co-authored-by: John Ericson <git@JohnEricson.me>
This commit is contained in:
Adam Joseph 2022-07-10 01:59:54 -07:00
parent 4f34f4a863
commit 36a566b78f

View file

@ -422,29 +422,29 @@ rec {
else if (elemAt l 1) == "elf"
then { cpu = elemAt l 0; vendor = "unknown"; kernel = "none"; abi = elemAt l 1; }
else { cpu = elemAt l 0; kernel = elemAt l 1; };
"3" = # Awkward hacks, beware!
if elemAt l 1 == "apple"
then { cpu = elemAt l 0; vendor = "apple"; kernel = elemAt l 2; }
else if (elemAt l 1 == "linux") || (elemAt l 2 == "gnu")
then { cpu = elemAt l 0; kernel = elemAt l 1; abi = elemAt l 2; }
else if (elemAt l 2 == "mingw32") # autotools breaks on -gnu for window
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "windows"; }
else if (elemAt l 2 == "wasi")
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "wasi"; }
else if (elemAt l 2 == "redox")
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "redox"; }
else if (elemAt l 2 == "mmixware")
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "mmixware"; }
else if hasPrefix "freebsd" (elemAt l 2)
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = elemAt l 2; }
else if hasPrefix "netbsd" (elemAt l 2)
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = elemAt l 2; }
else if (elem (elemAt l 2) ["eabi" "eabihf" "elf"])
then { cpu = elemAt l 0; vendor = "unknown"; kernel = elemAt l 1; abi = elemAt l 2; }
else if (elemAt l 2 == "ghcjs")
then { cpu = elemAt l 0; vendor = "unknown"; kernel = elemAt l 2; }
else if hasPrefix "genode" (elemAt l 2)
then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = elemAt l 2; }
"3" =
# cpu-kernel-environment
if elemAt l 1 == "linux" ||
elem (elemAt l 2) ["eabi" "eabihf" "elf" "gnu"]
then {
cpu = elemAt l 0;
kernel = elemAt l 1;
abi = elemAt l 2;
vendor = "unknown";
}
# cpu-vendor-os
else if elemAt l 1 == "apple" ||
elem (elemAt l 2) [ "wasi" "redox" "mmixware" "ghcjs" "mingw32" ] ||
hasPrefix "freebsd" (elemAt l 2) ||
hasPrefix "netbsd" (elemAt l 2) ||
hasPrefix "genode" (elemAt l 2)
then {
cpu = elemAt l 0;
vendor = elemAt l 1;
kernel = if elemAt l 2 == "mingw32"
then "windows" # autotools breaks on -gnu for window
else elemAt l 2;
}
else throw "Target specification with 3 components is ambiguous";
"4" = { cpu = elemAt l 0; vendor = elemAt l 1; kernel = elemAt l 2; abi = elemAt l 3; };
}.${toString (length l)}