lib: Infer `libc` field of platform if not specified

This is especially useful when not cross compiling. It means we can
remove the `stdenv.isGlibc` predicate too.

Additionally, use this to simplify the logic to choose the
appropriate libiconv derivation.

3 files changed, 19 insertions, 12 deletions

diff --git a/lib/systems/default.nix b/lib/systems/default.nix
index a61e4efc4ef..c37b6be2523 100644
--- a/lib/systems/default.nix
+++ b/lib/systems/default.nix
@@ -21,6 +21,12 @@ rec {
       config = parse.tripleFromSystem final.parsed;
       # Just a guess, based on `system`
       platform = platforms.selectBySystem final.system;
+      libc =
+        /**/ if final.isDarwin then "libSystem"
+        else if final.isMinGW  then "msvcrt"
+        else if final.isLinux  then "glibc"
+        # TODO(@Ericson2314) think more about other operating systems
+        else                        "native/impure";
     } // mapAttrs (n: v: v final.parsed) inspect.predicates
       // args;
   in final;
diff --git a/pkgs/stdenv/generic/default.nix b/pkgs/stdenv/generic/default.nix
index a063a1ed2dc..e029622dfa4 100644
--- a/pkgs/stdenv/generic/default.nix
+++ b/pkgs/stdenv/generic/default.nix
@@ -402,9 +402,6 @@ let
              || system == "aarch64-linux"
              || system == "mips64el-linux";
       isGNU = system == "i686-gnu"; # GNU/Hurd
-      isGlibc = isGNU # useful for `stdenvNative'
-             || isLinux
-             || system == "x86_64-kfreebsd-gnu";
       isSunOS = system == "i686-solaris"
              || system == "x86_64-solaris";
       isCygwin = system == "i686-cygwin"
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 88f4bc04b9f..a74fd79d6e7 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -8653,15 +8653,19 @@ with pkgs;
 
   libgsf = callPackage ../development/libraries/libgsf { };
 
-  # glibc provides libiconv so systems with glibc don't need to build libiconv
-  # separately, but we also provide libiconvReal, which will always be a
-  # standalone libiconv, just in case you want it
-  libiconv = if stdenv ? cross then
-    (if stdenv.cross.libc == "glibc" then libcCross
-      else if stdenv.cross.libc == "libSystem" then darwin.libiconv
-      else libiconvReal)
-    else if stdenv.isGlibc then glibcIconv stdenv.cc.libc
-    else if stdenv.isDarwin then darwin.libiconv
+  # GNU libc provides libiconv so systems with glibc don't need to build
+  # libiconv separately. Additionally, Apple forked/repackaged libiconv so we
+  # use that instead of the vanilla version on that OS.
+  #
+  # We also provide `libiconvReal`, which will always be a standalone libiconv,
+  # just in case you want it regardless of platform.
+  libiconv =
+    if hostPlatform.libc == "glibc"
+      then glibcIconv (if hostPlatform != buildPlatform
+                       then libcCross
+                       else stdenv.cc.libc)
+    else if hostPlatform.isDarwin
+      then darwin.libiconv
     else libiconvReal;
 
   glibcIconv = libc: let