lib/systems/inspect.nix: remove isPowerPC

Very confusingly, the `isPowerPC` predicate in
`lib/systems/inspect.nix` does *not* match `powerpc64le`!

This is because `isPowerPC` is defined as

  isPowerPC      = { cpu = cpuTypes.powerpc; };

Where `cpuTypes.powerpc` is:

  { bits = 32; significantByte = bigEndian; family = "power"; };

This means that the `isPowerPC` predicate actually only matches the
subset of machines marketed under this name which happen to be 32-bit
and running in big-endian mode which is equivalent to:

  with stdenv.hostPlatform; isPower && isBigEndian && is32bit

This seems like a sharp edge that people could easily cut themselves
on.  In fact, that has already happened: in
`linux/kernel/common-config.nix` there is a test which will always
fail:

  (stdenv.hostPlatform.isPowerPC && stdenv.hostPlatform.is64bit)

A more subtle case of the strict isPowerPC being used instead of the
moreg general isPower accidentally are the GHC expressions:

  Update pkgs/development/compilers/ghc/8.10.7.nix
  Update pkgs/development/compilers/ghc/8.8.4.nix
  Update pkgs/development/compilers/ghc/9.2.2.nix
  Update pkgs/development/compilers/ghc/9.0.2.nix
  Update pkgs/development/compilers/ghc/head.nix

Since the remaining legitimate use sites of isPowerPC are so few, remove
the isPowerPC predicate completely. The alternative expression above is
noted in the release notes as an alternative.

Co-authored-by: sternenseemann <sternenseemann@systemli.org>

11 files changed, 27 insertions, 10 deletions

diff --git a/lib/systems/inspect.nix b/lib/systems/inspect.nix
index 00cbe4f012c..e5bd879e2c4 100644
--- a/lib/systems/inspect.nix
+++ b/lib/systems/inspect.nix
@@ -11,7 +11,6 @@ rec {
     isi686         = { cpu = cpuTypes.i686; };
     isx86_32       = { cpu = { family = "x86"; bits = 32; }; };
     isx86_64       = { cpu = { family = "x86"; bits = 64; }; };
-    isPowerPC      = { cpu = cpuTypes.powerpc; };
     isPower        = { cpu = { family = "power"; }; };
     isPower64      = { cpu = { family = "power"; bits = 64; }; };
     isx86          = { cpu = { family = "x86"; }; };
diff --git a/nixos/doc/manual/from_md/release-notes/rl-2211.section.xml b/nixos/doc/manual/from_md/release-notes/rl-2211.section.xml
index 79268b398e6..908d1ab46e8 100644
--- a/nixos/doc/manual/from_md/release-notes/rl-2211.section.xml
+++ b/nixos/doc/manual/from_md/release-notes/rl-2211.section.xml
@@ -51,7 +51,7 @@
   </section>
   <section xml:id="sec-release-22.11-incompatibilities">
     <title>Backward Incompatibilities</title>
-    <itemizedlist spacing="compact">
+    <itemizedlist>
       <listitem>
         <para>
           The <literal>isCompatible</literal> predicate checking CPU
@@ -69,6 +69,21 @@
           compatible</emphasis>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The <literal>isPowerPC</literal> predicate, found on
+          <literal>platform</literal> attrsets
+          (<literal>hostPlatform</literal>,
+          <literal>buildPlatform</literal>,
+          <literal>targetPlatform</literal>, etc) has been removed in
+          order to reduce confusion. The predicate was was defined such
+          that it matches only the 32-bit big-endian members of the
+          POWER/PowerPC family, despite having a name which would imply
+          a broader set of systems. If you were using this predicate,
+          you can replace <literal>foo.isPowerPC</literal> with
+          <literal>(with foo; isPower &amp;&amp; is32bit &amp;&amp; isBigEndian)</literal>.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-22.11-notable-changes">
diff --git a/nixos/doc/manual/release-notes/rl-2211.section.md b/nixos/doc/manual/release-notes/rl-2211.section.md
index 7d2eacce57f..87fdf4e77f2 100644
--- a/nixos/doc/manual/release-notes/rl-2211.section.md
+++ b/nixos/doc/manual/release-notes/rl-2211.section.md
@@ -37,6 +37,9 @@ In addition to numerous new and upgraded packages, this release has the followin
   `lib.systems.parse.isCompatible` still exists, but has changed semantically:
   Architectures with differing endianness modes are *no longer considered compatible*.
 
+- The `isPowerPC` predicate, found on `platform` attrsets (`hostPlatform`, `buildPlatform`, `targetPlatform`, etc) has been removed in order to reduce confusion.  The predicate was was defined such that it matches only the 32-bit big-endian members of the POWER/PowerPC family, despite having a name which would imply a broader set of systems.  If you were using this predicate, you can replace `foo.isPowerPC` with `(with foo; isPower && is32bit && isBigEndian)`.
+
+
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
 ## Other Notable Changes {#sec-release-22.11-notable-changes}
diff --git a/nixos/modules/installer/cd-dvd/iso-image.nix b/nixos/modules/installer/cd-dvd/iso-image.nix
index 1eaa940afb1..d1ccc6c2072 100644
--- a/nixos/modules/installer/cd-dvd/iso-image.nix
+++ b/nixos/modules/installer/cd-dvd/iso-image.nix
@@ -479,7 +479,7 @@ in
                 + lib.optionalString (isx86_32 || isx86_64) "-Xbcj x86"
                 # Untested but should also reduce size for these platforms
                 + lib.optionalString (isAarch32 || isAarch64) "-Xbcj arm"
-                + lib.optionalString (isPowerPC) "-Xbcj powerpc"
+                + lib.optionalString (isPower && is32bit && isBigEndian) "-Xbcj powerpc"
                 + lib.optionalString (isSparc) "-Xbcj sparc";
       description = ''
         Compression settings to use for the squashfs nix store.
diff --git a/pkgs/development/compilers/ghc/8.10.7.nix b/pkgs/development/compilers/ghc/8.10.7.nix
index cdf4faf3ffc..7a56d7c0e5c 100644
--- a/pkgs/development/compilers/ghc/8.10.7.nix
+++ b/pkgs/development/compilers/ghc/8.10.7.nix
@@ -12,7 +12,7 @@
   libffi ? null
 
 , useLLVM ? !(stdenv.targetPlatform.isx86
-              || stdenv.targetPlatform.isPowerPC
+              || stdenv.targetPlatform.isPower
               || stdenv.targetPlatform.isSparc)
 , # LLVM is conceptually a run-time-only depedendency, but for
   # non-x86, we need LLVM to bootstrap later stages, so it becomes a
diff --git a/pkgs/development/compilers/ghc/8.8.4.nix b/pkgs/development/compilers/ghc/8.8.4.nix
index af01582b108..907d995a250 100644
--- a/pkgs/development/compilers/ghc/8.8.4.nix
+++ b/pkgs/development/compilers/ghc/8.8.4.nix
@@ -11,7 +11,7 @@
   libffi ? null
 
 , useLLVM ? !(stdenv.targetPlatform.isx86
-              || stdenv.targetPlatform.isPowerPC
+              || stdenv.targetPlatform.isPower
               || stdenv.targetPlatform.isSparc)
 , # LLVM is conceptually a run-time-only depedendency, but for
   # non-x86, we need LLVM to bootstrap later stages, so it becomes a
diff --git a/pkgs/development/compilers/ghc/9.0.2.nix b/pkgs/development/compilers/ghc/9.0.2.nix
index a4cefe7294d..6de0f201599 100644
--- a/pkgs/development/compilers/ghc/9.0.2.nix
+++ b/pkgs/development/compilers/ghc/9.0.2.nix
@@ -14,7 +14,7 @@
   libffi ? null
 
 , useLLVM ? !(stdenv.targetPlatform.isx86
-              || stdenv.targetPlatform.isPowerPC
+              || stdenv.targetPlatform.isPower
               || stdenv.targetPlatform.isSparc)
 , # LLVM is conceptually a run-time-only depedendency, but for
   # non-x86, we need LLVM to bootstrap later stages, so it becomes a
diff --git a/pkgs/development/compilers/ghc/9.2.2.nix b/pkgs/development/compilers/ghc/9.2.2.nix
index 0a572bff7ef..880db433789 100644
--- a/pkgs/development/compilers/ghc/9.2.2.nix
+++ b/pkgs/development/compilers/ghc/9.2.2.nix
@@ -13,7 +13,7 @@
   libffi ? null
 
 , useLLVM ? !(stdenv.targetPlatform.isx86
-              || stdenv.targetPlatform.isPowerPC
+              || stdenv.targetPlatform.isPower
               || stdenv.targetPlatform.isSparc
               || (stdenv.targetPlatform.isAarch64 && stdenv.targetPlatform.isDarwin))
 , # LLVM is conceptually a run-time-only depedendency, but for
diff --git a/pkgs/development/compilers/ghc/head.nix b/pkgs/development/compilers/ghc/head.nix
index a2afb7400c2..4f52ba0a618 100644
--- a/pkgs/development/compilers/ghc/head.nix
+++ b/pkgs/development/compilers/ghc/head.nix
@@ -19,7 +19,7 @@
 , elfutils # for DWARF support
 
 , useLLVM ? !(stdenv.targetPlatform.isx86
-              || stdenv.targetPlatform.isPowerPC
+              || stdenv.targetPlatform.isPower
               || stdenv.targetPlatform.isSparc
               || (stdenv.targetPlatform.isAarch64 && stdenv.targetPlatform.isDarwin))
 , # LLVM is conceptually a run-time-only depedendency, but for
diff --git a/pkgs/os-specific/linux/kernel-headers/default.nix b/pkgs/os-specific/linux/kernel-headers/default.nix
index 0c1514d01c2..aa9f4e3763b 100644
--- a/pkgs/os-specific/linux/kernel-headers/default.nix
+++ b/pkgs/os-specific/linux/kernel-headers/default.nix
@@ -24,7 +24,7 @@ let
       flex bison python rsync
     ];
 
-    extraIncludeDirs = lib.optional stdenvNoCC.hostPlatform.isPowerPC ["ppc"];
+    extraIncludeDirs = lib.optional (with stdenvNoCC.hostPlatform; isPower && is32bit && isBigEndian) ["ppc"];
 
     inherit patches;
 
diff --git a/pkgs/os-specific/linux/kernel/common-config.nix b/pkgs/os-specific/linux/kernel/common-config.nix
index d25e20bac8b..4b6cceba238 100644
--- a/pkgs/os-specific/linux/kernel/common-config.nix
+++ b/pkgs/os-specific/linux/kernel/common-config.nix
@@ -29,7 +29,7 @@ let
     mkIf (stdenv.hostPlatform.isAarch32 ||
           stdenv.hostPlatform.isAarch64 ||
           stdenv.hostPlatform.isx86_64 ||
-          (stdenv.hostPlatform.isPowerPC && stdenv.hostPlatform.is64bit) ||
+          (stdenv.hostPlatform.isPower && stdenv.hostPlatform.is64bit) ||
           (stdenv.hostPlatform.isMips && stdenv.hostPlatform.is64bit));
 
   options = {