From 8c9c583f7c8669141e01f25dbd61ffdaefc88398 Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:06:15 +0000
Subject: [PATCH 01/13] cygwin: init as a target toolchain

---
 lib/systems/examples.nix | 5 +++++
 lib/systems/parse.nix    | 9 ++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/systems/examples.nix b/lib/systems/examples.nix
index 20f96f0849d16..b6c90ee113909 100644
--- a/lib/systems/examples.nix
+++ b/lib/systems/examples.nix
@@ -332,6 +332,11 @@ rec {
     useLLVM = true;
   };
 
+  x86_64-cygwin = {
+    config = "x86_64-pc-cygwin";
+    libc = "cygwin"; # cygwin (posix) toolchain
+  };
+
   # BSDs
 
   x86_64-freebsd = {
diff --git a/lib/systems/parse.nix b/lib/systems/parse.nix
index a2ee288f2c1f8..88e49288d5fd7 100644
--- a/lib/systems/parse.nix
+++ b/lib/systems/parse.nix
@@ -444,7 +444,7 @@ rec {
       else throw "Target specification with 1 components is ambiguous";
     "2" = # We only do 2-part hacks for things Nix already supports
       if elemAt l 1 == "cygwin"
-        then { cpu = elemAt l 0;                      kernel = "windows";  abi = "cygnus";   }
+        then mkSkeletonFromList [ (elemAt l 0) "pc" "cygwin" ]
       # MSVC ought to be the default ABI so this case isn't needed. But then it
       # becomes difficult to handle the gnu* variants for Aarch32 correctly for
       # minGW. So it's easier to make gnu* the default for the MinGW, but
@@ -479,6 +479,13 @@ rec {
                  then "windows"  # autotools breaks on -gnu for window
                  else elemAt l 2;
       }
+      # lots of tools expect a triplet for Cygwin, even though the vendor is just "pc"
+      else if elemAt l 2 == "cygwin"
+      then {
+        cpu = elemAt l 0;
+        kernel = "windows";
+        abi = "cygnus";
+      }
       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)}

From 12c6e6224f25799c4f3ae1340498dd41a498285e Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:10:40 +0000
Subject: [PATCH 02/13] cygwin: add pre-libc headers

---
 .../compilers/gcc/common/configure-flags.nix  |  4 ++
 pkgs/os-specific/windows/cygwin/headers.nix   | 40 +++++++++++++++++++
 pkgs/os-specific/windows/default.nix          |  1 +
 .../os-specific/windows/mingw-w64/headers.nix |  2 +
 pkgs/top-level/all-packages.nix               |  1 +
 5 files changed, 48 insertions(+)
 create mode 100644 pkgs/os-specific/windows/cygwin/headers.nix

diff --git a/pkgs/development/compilers/gcc/common/configure-flags.nix b/pkgs/development/compilers/gcc/common/configure-flags.nix
index 25d4f1f53bae9..9d33891d661db 100644
--- a/pkgs/development/compilers/gcc/common/configure-flags.nix
+++ b/pkgs/development/compilers/gcc/common/configure-flags.nix
@@ -242,6 +242,10 @@ let
       #   cc1: error: fp software completion requires '-mtrap-precision=i' [-Werror]
       "--disable-werror"
     ]
+    ++ lib.optionals targetPlatform.isCygwin [
+      # doesn't cross-compile under Cygwin
+      "--disable-libvtv"
+    ]
   ;
 
 in configureFlags
diff --git a/pkgs/os-specific/windows/cygwin/headers.nix b/pkgs/os-specific/windows/cygwin/headers.nix
new file mode 100644
index 0000000000000..ecceb372b0805
--- /dev/null
+++ b/pkgs/os-specific/windows/cygwin/headers.nix
@@ -0,0 +1,40 @@
+{
+  lib,
+  stdenvNoCC,
+  fetchFromGitHub,
+  fetchpatch,
+  mingw_w64_headers,
+}:
+
+stdenvNoCC.mkDerivation (finalAttrs: {
+  pname = "cygwin-headers";
+  version = "3.5.4";
+
+  src = fetchFromGitHub {
+    owner = "mirror";
+    repo = "newlib-cygwin";
+    rev = "cygwin-${finalAttrs.version}";
+    hash = "sha256-ZfT6JhOXLCJOY0vSVz6aKShmtuTN9/0NZ1k1RMSZX4Q=";
+  };
+
+  patches = [
+    (fetchpatch {
+      url = "https://raw.githubusercontent.com/Windows-on-ARM-Experiments/mingw-woarm64-build/371102dfa23b3e56b6759e1a44026d0640d55223/patches/cygwin/0001-before-autogen.patch";
+      sha256 = "sha256-1JsbfYAPpsQSjknZcKfJOHA0RcdmgzkzAI4RcHG1kpA=";
+    })
+  ];
+
+  dontConfigure = true;
+  dontBuild = true;
+
+  installPhase = ''
+    mkdir -p $out/include/
+    ln -s ${mingw_w64_headers}/include/w32api $out/include/
+    cp -r newlib/libc/include/* $out/include/
+    cp -r winsup/cygwin/include/* $out/include/
+  '';
+
+  meta = {
+    platforms = lib.platforms.windows;
+  };
+})
diff --git a/pkgs/os-specific/windows/default.nix b/pkgs/os-specific/windows/default.nix
index 59806318a23ec..3e7fd4912060e 100644
--- a/pkgs/os-specific/windows/default.nix
+++ b/pkgs/os-specific/windows/default.nix
@@ -16,6 +16,7 @@ lib.makeScope newScope (
     dlfcn = callPackage ./dlfcn { };
 
     w32api = callPackage ./w32api { };
+    cygwin_headers = callPackage ./cygwin/headers.nix { };
 
     mingwrt = callPackage ./mingwrt { };
     mingw_runtime = mingwrt;
diff --git a/pkgs/os-specific/windows/mingw-w64/headers.nix b/pkgs/os-specific/windows/mingw-w64/headers.nix
index daae7ee0aa42a..78bee797ac0fa 100644
--- a/pkgs/os-specific/windows/mingw-w64/headers.nix
+++ b/pkgs/os-specific/windows/mingw-w64/headers.nix
@@ -17,6 +17,8 @@ stdenvNoCC.mkDerivation (finalAttrs: {
     cd mingw-w64-headers
   '';
 
+  configureFlags = lib.optionals stdenvNoCC.targetPlatform.isCygwin [ "--enable-w32api" ];
+
   meta = {
     platforms = lib.platforms.windows;
   };
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 2963ef53755a0..2b51ec2f307ee 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -19546,6 +19546,7 @@ with pkgs;
   preLibcCrossHeaders = let
     inherit (stdenv.targetPlatform) libc;
   in     if stdenv.targetPlatform.isMinGW then targetPackages.windows.mingw_w64_headers or windows.mingw_w64_headers
+    else if stdenv.targetPlatform.isCygwin then targetPackages.windows.cygwin_headers or windows.cygwin_headers
     else if libc == "nblibc" then targetPackages.netbsd.headers or netbsd.headers
     else null;
 

From e670bc62dda26d65b9a476f28c061721b61e8bb0 Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:13:55 +0000
Subject: [PATCH 03/13] cygwin: remove old w32api, it's in mingw-w64

---
 pkgs/os-specific/windows/default.nix          |  1 -
 .../os-specific/windows/mingw-w64/default.nix |  5 +++--
 pkgs/os-specific/windows/w32api/default.nix   | 21 -------------------
 3 files changed, 3 insertions(+), 24 deletions(-)
 delete mode 100644 pkgs/os-specific/windows/w32api/default.nix

diff --git a/pkgs/os-specific/windows/default.nix b/pkgs/os-specific/windows/default.nix
index 3e7fd4912060e..e886ce2c6b6fe 100644
--- a/pkgs/os-specific/windows/default.nix
+++ b/pkgs/os-specific/windows/default.nix
@@ -15,7 +15,6 @@ lib.makeScope newScope (
 
     dlfcn = callPackage ./dlfcn { };
 
-    w32api = callPackage ./w32api { };
     cygwin_headers = callPackage ./cygwin/headers.nix { };
 
     mingwrt = callPackage ./mingwrt { };
diff --git a/pkgs/os-specific/windows/mingw-w64/default.nix b/pkgs/os-specific/windows/mingw-w64/default.nix
index d8103d7b8d37d..1f2b04d7a89fd 100644
--- a/pkgs/os-specific/windows/mingw-w64/default.nix
+++ b/pkgs/os-specific/windows/mingw-w64/default.nix
@@ -22,8 +22,9 @@ stdenv.mkDerivation {
   ];
 
   configureFlags = [
-    (lib.enableFeature true "idl")
-    (lib.enableFeature true "secure-api")
+    (lib.enableFeature stdenv.targetPlatform.isMinGW "idl")
+    (lib.enableFeature stdenv.targetPlatform.isMinGW "secure-api")
+    (lib.enableFeature stdenv.targetPlatform.isCygwin "w32api")
     (lib.withFeatureAs true "default-msvcrt" crt)
 
     # Including other architectures causes errors with invalid asm
diff --git a/pkgs/os-specific/windows/w32api/default.nix b/pkgs/os-specific/windows/w32api/default.nix
deleted file mode 100644
index e368338525664..0000000000000
--- a/pkgs/os-specific/windows/w32api/default.nix
+++ /dev/null
@@ -1,21 +0,0 @@
-{
-  stdenv,
-  fetchurl,
-  lib,
-}:
-
-stdenv.mkDerivation rec {
-  pname = "w32api";
-  version = "3.17-2";
-
-  src = fetchurl {
-    url = "mirror://sourceforge/mingw/MinGW/Base/w32api/w32api-${lib.versions.majorMinor version}/w32api-${version}-mingw32-src.tar.lzma";
-    sha256 = "09rhnl6zikmdyb960im55jck0rdy5z9nlg3akx68ixn7khf3j8wb";
-  };
-
-  meta = {
-    platforms = lib.platforms.windows;
-  };
-
-  dontStrip = true;
-}

From b6262e05e9cc883dd94345d13e24d7d53af7b6cb Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:15:52 +0000
Subject: [PATCH 04/13] cocom-tool-set: init at 0.996

---
 pkgs/by-name/co/cocom-tool-set/package.nix    | 28 +++++++++++++
 .../co/cocom-tool-set/remove-lto.patch        | 42 +++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100644 pkgs/by-name/co/cocom-tool-set/package.nix
 create mode 100644 pkgs/by-name/co/cocom-tool-set/remove-lto.patch

diff --git a/pkgs/by-name/co/cocom-tool-set/package.nix b/pkgs/by-name/co/cocom-tool-set/package.nix
new file mode 100644
index 0000000000000..c0a3409c04a03
--- /dev/null
+++ b/pkgs/by-name/co/cocom-tool-set/package.nix
@@ -0,0 +1,28 @@
+{
+  lib,
+  stdenv,
+  fetchgit,
+  bison,
+}:
+stdenv.mkDerivation {
+  pname = "cocom";
+  version = "0.996";
+
+  src = fetchgit {
+    url = "https://git.code.sf.net/p/cocom/git";
+    sha256 = "sha256-utLafkznMC4LrZgF6vKehtIGMwNMwLP9M9Nwu/RyWio=";
+    rev = "64ee80224aa13f9944d439f3f90862ca76158705";
+  };
+
+  nativeBuildInputs = [ bison ];
+
+  patches = [ ./remove-lto.patch ];
+
+  meta = {
+    description = "Tool set oriented towards the creation of compilers";
+    homepage = "https://cocom.sourceforge.net/";
+    license = lib.licenses.gpl2Plus;
+    maintainers = with lib.maintainers; [ puffnfresh ];
+    platforms = lib.platforms.linux;
+  };
+}
diff --git a/pkgs/by-name/co/cocom-tool-set/remove-lto.patch b/pkgs/by-name/co/cocom-tool-set/remove-lto.patch
new file mode 100644
index 0000000000000..0726a1b8b0162
--- /dev/null
+++ b/pkgs/by-name/co/cocom-tool-set/remove-lto.patch
@@ -0,0 +1,42 @@
+diff --git a/configure b/configure
+index 574cbe9..0dc2aa0 100755
+--- a/configure
++++ b/configure
+@@ -5858,37 +5858,6 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+     CXXFLAGS="`echo $CXXFLAGS|sed s/-O2//` -O3"
+   fi
+ 
+-  my_save_cflags="$CFLAGS"
+-  CFLAGS=-flto
+-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether CC supports -flto" >&5
+-$as_echo_n "checking whether CC supports -flto... " >&6; }
+-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+-/* end confdefs.h.  */
+-
+-int
+-main ()
+-{
+-
+-  ;
+-  return 0;
+-}
+-_ACEOF
+-if ac_fn_c_try_compile "$LINENO"; then :
+-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+-$as_echo "yes" >&6; }
+-      lto=yes
+-else
+-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+-$as_echo "no" >&6; }
+-
+-fi
+-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+-  CFLAGS="$my_save_cflags"
+-  if test "$lto" = yes; then
+-    CFLAGS="`echo $CFLAGS` -flto"
+-    CXXFLAGS="`echo $CXXFLAGS` -flto"
+-  fi
+-
+   system=`uname -m`
+   case $system in
+ 	i386*|i486*|i586*|i686*)

From 4ecdadfa9ae80270a0ff4946d257a75e920b26db Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:17:26 +0000
Subject: [PATCH 05/13] cygwin: package newlib-cygwin as the libc

---
 pkgs/development/compilers/gcc/default.nix    |   7 +-
 .../windows/cygwin/after-autogen.patch        | 158 ++++++++++++++++++
 pkgs/os-specific/windows/cygwin/default.nix   |  65 +++++++
 pkgs/os-specific/windows/default.nix          |   3 +
 .../os-specific/windows/mingw-w64/default.nix |  16 ++
 pkgs/top-level/all-packages.nix               |   3 +-
 6 files changed, 250 insertions(+), 2 deletions(-)
 create mode 100644 pkgs/os-specific/windows/cygwin/after-autogen.patch
 create mode 100644 pkgs/os-specific/windows/cygwin/default.nix

diff --git a/pkgs/development/compilers/gcc/default.nix b/pkgs/development/compilers/gcc/default.nix
index d5d59adabb74c..8e682b419f0d2 100644
--- a/pkgs/development/compilers/gcc/default.nix
+++ b/pkgs/development/compilers/gcc/default.nix
@@ -245,7 +245,12 @@ pipe ((callFile ./common/builder.nix {}) ({
                '-s' # workaround for hitting hydra log limit
                'LIMITS_H_TEST=false'
             )
-          '');
+          '')
+      + optionalString targetPlatform.isCygwin (''
+        substituteInPlace gcc/config/i386/cygwin.h \
+          --replace '../../include/w32api' "${libcCross}/include/w32api" \
+          --replace '../include/w32api' "${libcCross}/include/w32api"
+      '');
 
   inherit noSysDirs staticCompiler withoutTargetLibc
     libcCross crossMingw;
diff --git a/pkgs/os-specific/windows/cygwin/after-autogen.patch b/pkgs/os-specific/windows/cygwin/after-autogen.patch
new file mode 100644
index 0000000000000..fa4748093e332
--- /dev/null
+++ b/pkgs/os-specific/windows/cygwin/after-autogen.patch
@@ -0,0 +1,158 @@
+--- winsup/configure.old	2024-11-01 22:38:21.005768397 +1100
++++ winsup/configure	2024-11-01 22:39:33.247435255 +1100
+@@ -3970,155 +3970,6 @@
+ _ACEOF
+ ac_clean_files_save=$ac_clean_files
+ ac_clean_files="$ac_clean_files a.out a.out.dSYM a.exe b.out"
+-# Try to create an executable without -o first, disregard a.out.
+-# It will help us diagnose broken compilers, and finding out an intuition
+-# of exeext.
+-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether the C compiler works" >&5
+-printf %s "checking whether the C compiler works... " >&6; }
+-ac_link_default=`printf "%s\n" "$ac_link" | sed 's/ -o *conftest[^ ]*//'`
+-
+-# The possible output files:
+-ac_files="a.out conftest.exe conftest a.exe a_out.exe b.out conftest.*"
+-
+-ac_rmfiles=
+-for ac_file in $ac_files
+-do
+-  case $ac_file in
+-    *.$ac_ext | *.xcoff | *.tds | *.d | *.pdb | *.xSYM | *.bb | *.bbg | *.map | *.inf | *.dSYM | *.o | *.obj ) ;;
+-    * ) ac_rmfiles="$ac_rmfiles $ac_file";;
+-  esac
+-done
+-rm -f $ac_rmfiles
+-
+-if { { ac_try="$ac_link_default"
+-case "(($ac_try" in
+-  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+-  *) ac_try_echo=$ac_try;;
+-esac
+-eval ac_try_echo="\"\$as_me:${as_lineno-$LINENO}: $ac_try_echo\""
+-printf "%s\n" "$ac_try_echo"; } >&5
+-  (eval "$ac_link_default") 2>&5
+-  ac_status=$?
+-  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+-  test $ac_status = 0; }
+-then :
+-  # Autoconf-2.13 could set the ac_cv_exeext variable to 'no'.
+-# So ignore a value of 'no', otherwise this would lead to 'EXEEXT = no'
+-# in a Makefile.  We should not override ac_cv_exeext if it was cached,
+-# so that the user can short-circuit this test for compilers unknown to
+-# Autoconf.
+-for ac_file in $ac_files ''
+-do
+-  test -f "$ac_file" || continue
+-  case $ac_file in
+-    *.$ac_ext | *.xcoff | *.tds | *.d | *.pdb | *.xSYM | *.bb | *.bbg | *.map | *.inf | *.dSYM | *.o | *.obj )
+-	;;
+-    [ab].out )
+-	# We found the default executable, but exeext='' is most
+-	# certainly right.
+-	break;;
+-    *.* )
+-	if test ${ac_cv_exeext+y} && test "$ac_cv_exeext" != no;
+-	then :; else
+-	   ac_cv_exeext=`expr "$ac_file" : '[^.]*\(\..*\)'`
+-	fi
+-	# We set ac_cv_exeext here because the later test for it is not
+-	# safe: cross compilers may not add the suffix if given an '-o'
+-	# argument, so we may need to know it at that point already.
+-	# Even if this section looks crufty: it has the advantage of
+-	# actually working.
+-	break;;
+-    * )
+-	break;;
+-  esac
+-done
+-test "$ac_cv_exeext" = no && ac_cv_exeext=
+-
+-else case e in #(
+-  e) ac_file='' ;;
+-esac
+-fi
+-if test -z "$ac_file"
+-then :
+-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+-printf "%s\n" "no" >&6; }
+-printf "%s\n" "$as_me: failed program was:" >&5
+-sed 's/^/| /' conftest.$ac_ext >&5
+-
+-{ { printf "%s\n" "$as_me:${as_lineno-$LINENO}: error: in '$ac_pwd':" >&5
+-printf "%s\n" "$as_me: error: in '$ac_pwd':" >&2;}
+-as_fn_error 77 "C compiler cannot create executables
+-See 'config.log' for more details" "$LINENO" 5; }
+-else case e in #(
+-  e) { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+-printf "%s\n" "yes" >&6; } ;;
+-esac
+-fi
+-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for C compiler default output file name" >&5
+-printf %s "checking for C compiler default output file name... " >&6; }
+-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_file" >&5
+-printf "%s\n" "$ac_file" >&6; }
+-ac_exeext=$ac_cv_exeext
+-
+-rm -f -r a.out a.out.dSYM a.exe conftest$ac_cv_exeext b.out
+-ac_clean_files=$ac_clean_files_save
+-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for suffix of executables" >&5
+-printf %s "checking for suffix of executables... " >&6; }
+-if { { ac_try="$ac_link"
+-case "(($ac_try" in
+-  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+-  *) ac_try_echo=$ac_try;;
+-esac
+-eval ac_try_echo="\"\$as_me:${as_lineno-$LINENO}: $ac_try_echo\""
+-printf "%s\n" "$ac_try_echo"; } >&5
+-  (eval "$ac_link") 2>&5
+-  ac_status=$?
+-  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+-  test $ac_status = 0; }
+-then :
+-  # If both 'conftest.exe' and 'conftest' are 'present' (well, observable)
+-# catch 'conftest.exe'.  For instance with Cygwin, 'ls conftest' will
+-# work properly (i.e., refer to 'conftest.exe'), while it won't with
+-# 'rm'.
+-for ac_file in conftest.exe conftest conftest.*; do
+-  test -f "$ac_file" || continue
+-  case $ac_file in
+-    *.$ac_ext | *.xcoff | *.tds | *.d | *.pdb | *.xSYM | *.bb | *.bbg | *.map | *.inf | *.dSYM | *.o | *.obj ) ;;
+-    *.* ) ac_cv_exeext=`expr "$ac_file" : '[^.]*\(\..*\)'`
+-	  break;;
+-    * ) break;;
+-  esac
+-done
+-else case e in #(
+-  e) { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: error: in '$ac_pwd':" >&5
+-printf "%s\n" "$as_me: error: in '$ac_pwd':" >&2;}
+-as_fn_error $? "cannot compute suffix of executables: cannot compile and link
+-See 'config.log' for more details" "$LINENO" 5; } ;;
+-esac
+-fi
+-rm -f conftest conftest$ac_cv_exeext
+-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_cv_exeext" >&5
+-printf "%s\n" "$ac_cv_exeext" >&6; }
+-
+-rm -f conftest.$ac_ext
+-EXEEXT=$ac_cv_exeext
+-ac_exeext=$EXEEXT
+-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+-/* end confdefs.h.  */
+-#include <stdio.h>
+-int
+-main (void)
+-{
+-FILE *f = fopen ("conftest.out", "w");
+- if (!f)
+-  return 1;
+- return ferror (f) || fclose (f) != 0;
+-
+-  ;
+-  return 0;
+-}
+-_ACEOF
+-ac_clean_files="$ac_clean_files conftest.out"
+ # Check that the compiler produces executables we can run.  If not, either
+ # the compiler is broken, or we cross compile.
+ { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether we are cross compiling" >&5
diff --git a/pkgs/os-specific/windows/cygwin/default.nix b/pkgs/os-specific/windows/cygwin/default.nix
new file mode 100644
index 0000000000000..a5b95f2b5b902
--- /dev/null
+++ b/pkgs/os-specific/windows/cygwin/default.nix
@@ -0,0 +1,65 @@
+{
+  lib,
+  stdenv,
+  cygwin_headers,
+  buildPackages,
+  automake,
+  autoconf,
+  bison,
+  cocom-tool-set,
+  flex,
+  perl,
+  mingw_w64,
+}:
+
+stdenv.mkDerivation {
+  pname = "cygwin";
+
+  inherit (cygwin_headers)
+    version
+    src
+    meta
+    patches
+    ;
+
+  preConfigure = ''
+    pushd winsup
+    aclocal --force
+    autoconf -f
+    automake -ac
+    rm -rf autom4te.cache
+    popd
+    patch -p0 -i ${./after-autogen.patch}
+  '';
+
+  postPatch = ''
+    patchShebangs --build winsup/cygwin/scripts
+  '';
+
+  env.CXXFLAGS_FOR_TARGET = "-Wno-error";
+
+  depsBuildBuild = [ buildPackages.stdenv.cc ];
+  nativeBuildInputs = [
+    autoconf
+    automake
+    bison
+    cocom-tool-set
+    flex
+    perl
+  ];
+  buildInputs = [ mingw_w64 ];
+
+  hardeningDisable = [ "fortify" ];
+  configurePlatforms = [
+    "build"
+    "target"
+  ];
+  configureFlags = [
+    "--disable-shared"
+    "--disable-doc"
+    "--enable-static"
+    "--disable-dumper"
+    "--with-cross-bootstrap"
+    "ac_cv_prog_CC=gcc"
+  ];
+}
diff --git a/pkgs/os-specific/windows/default.nix b/pkgs/os-specific/windows/default.nix
index e886ce2c6b6fe..00e88760d86d6 100644
--- a/pkgs/os-specific/windows/default.nix
+++ b/pkgs/os-specific/windows/default.nix
@@ -15,6 +15,9 @@ lib.makeScope newScope (
 
     dlfcn = callPackage ./dlfcn { };
 
+    cygwin = callPackage ./cygwin {
+      stdenv = stdenvNoLibc;
+    };
     cygwin_headers = callPackage ./cygwin/headers.nix { };
 
     mingwrt = callPackage ./mingwrt { };
diff --git a/pkgs/os-specific/windows/mingw-w64/default.nix b/pkgs/os-specific/windows/mingw-w64/default.nix
index 1f2b04d7a89fd..d490debcebb0f 100644
--- a/pkgs/os-specific/windows/mingw-w64/default.nix
+++ b/pkgs/os-specific/windows/mingw-w64/default.nix
@@ -33,6 +33,22 @@ stdenv.mkDerivation {
     (lib.enableFeature stdenv.hostPlatform.isAarch64 "libarm64")
   ];
 
+  postInstall = lib.optionalString stdenv.targetPlatform.isCygwin ''
+    cd $out/lib
+    ln -fs w32api/libkernel32.a .
+    ln -fs w32api/libuser32.a .
+    ln -fs w32api/libadvapi32.a .
+    ln -fs w32api/libshell32.a .
+    ln -fs w32api/libgdi32.a .
+    ln -fs w32api/libcomdlg32.a .
+    ln -fs w32api/libntdll.a .
+    ln -fs w32api/libnetapi32.a .
+    ln -fs w32api/libpsapi.a .
+    ln -fs w32api/libuserenv.a .
+    ln -fs w32api/libnetapi32.a .
+    ln -fs w32api/libdbghelp.a .
+  '';
+
   enableParallelBuilding = true;
 
   nativeBuildInputs = [ autoreconfHook ];
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 2b51ec2f307ee..fef945edbb7aa 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -14462,7 +14462,7 @@ with pkgs;
         isl = if !stdenv.hostPlatform.isDarwin then isl_0_20 else null;
 
         withoutTargetLibc = true;
-        langCC = false;
+        langCC = stdenv.targetPlatform.isCygwin; # can't compile libcygwin1.a without C++
         libcCross = libcCross1;
         targetPackages.stdenv.cc.bintools = binutilsNoLibc;
         enableShared =
@@ -19567,6 +19567,7 @@ with pkgs;
     else if name == "musl" then targetPackages.muslCross or muslCross
     else if name == "msvcrt" then targetPackages.windows.mingw_w64 or windows.mingw_w64
     else if name == "ucrt" then targetPackages.windows.mingw_w64 or windows.mingw_w64
+    else if name == "cygwin" then targetPackages.windows.cygwin or windows.cygwin
     else if name == "libSystem" then
       if stdenv.targetPlatform.useiOSPrebuilt
       then targetPackages.darwin.iosSdkPkgs.libraries or darwin.iosSdkPkgs.libraries

From 85dd4c2a0385b73ddee90b382f6d998a41d25adf Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:25:26 +0000
Subject: [PATCH 06/13] cygwin: create libc from joined newlib-cygwin and
 mingw_w64

---
 pkgs/os-specific/windows/cygwin/default.nix | 107 ++++++++++++--------
 1 file changed, 64 insertions(+), 43 deletions(-)

diff --git a/pkgs/os-specific/windows/cygwin/default.nix b/pkgs/os-specific/windows/cygwin/default.nix
index a5b95f2b5b902..6f2ed2cf3729f 100644
--- a/pkgs/os-specific/windows/cygwin/default.nix
+++ b/pkgs/os-specific/windows/cygwin/default.nix
@@ -10,56 +10,77 @@
   flex,
   perl,
   mingw_w64,
+  symlinkJoin,
 }:
 
-stdenv.mkDerivation {
-  pname = "cygwin";
+let
+  newlib-cygwin = stdenv.mkDerivation {
+    pname = "cygwin";
 
-  inherit (cygwin_headers)
-    version
-    src
-    meta
-    patches
-    ;
+    inherit (cygwin_headers)
+      version
+      src
+      meta
+      patches
+      ;
 
-  preConfigure = ''
-    pushd winsup
-    aclocal --force
-    autoconf -f
-    automake -ac
-    rm -rf autom4te.cache
-    popd
-    patch -p0 -i ${./after-autogen.patch}
-  '';
+    preConfigure = ''
+      pushd winsup
+      aclocal --force
+      autoconf -f
+      automake -ac
+      rm -rf autom4te.cache
+      popd
+      patch -p0 -i ${./after-autogen.patch}
+    '';
 
-  postPatch = ''
-    patchShebangs --build winsup/cygwin/scripts
-  '';
+    postPatch = ''
+      patchShebangs --build winsup/cygwin/scripts
+    '';
 
-  env.CXXFLAGS_FOR_TARGET = "-Wno-error";
+    env.CXXFLAGS_FOR_TARGET = "-Wno-error";
 
-  depsBuildBuild = [ buildPackages.stdenv.cc ];
-  nativeBuildInputs = [
-    autoconf
-    automake
-    bison
-    cocom-tool-set
-    flex
-    perl
-  ];
-  buildInputs = [ mingw_w64 ];
+    depsBuildBuild = [ buildPackages.stdenv.cc ];
+    nativeBuildInputs = [
+      autoconf
+      automake
+      bison
+      cocom-tool-set
+      flex
+      perl
+    ];
+    buildInputs = [ mingw_w64 ];
 
-  hardeningDisable = [ "fortify" ];
-  configurePlatforms = [
-    "build"
-    "target"
-  ];
-  configureFlags = [
-    "--disable-shared"
-    "--disable-doc"
-    "--enable-static"
-    "--disable-dumper"
-    "--with-cross-bootstrap"
-    "ac_cv_prog_CC=gcc"
+    postInstall = ''
+      mv $out/x86_64-pc-cygwin/* $out/
+      rmdir $out/x86_64-pc-cygwin
+    '';
+
+    hardeningDisable = [
+      "fortify"
+      "stackprotector"
+    ];
+    configurePlatforms = [
+      "build"
+      "target"
+    ];
+    configureFlags = [
+      "--disable-shared"
+      "--disable-doc"
+      "--enable-static"
+      "--disable-dumper"
+      "--with-cross-bootstrap"
+      "ac_cv_prog_CC=gcc"
+    ];
+  };
+in
+# TODO: Is there something like nix-support which would achieve this better?
+symlinkJoin {
+  pname = "cygwin-and-mingw_w64";
+  inherit (newlib-cygwin) version;
+  paths = [
+    newlib-cygwin
+    mingw_w64
+    mingw_w64.dev
   ];
 }

From 8692585ef3fdff570e56747fe75f34e8e08da0dc Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:26:47 +0000
Subject: [PATCH 07/13] readline: fix compilation under Cygwin

---
 pkgs/development/libraries/readline/8.2.nix | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/pkgs/development/libraries/readline/8.2.nix b/pkgs/development/libraries/readline/8.2.nix
index 7bf5caf4060f1..40833dec2533d 100644
--- a/pkgs/development/libraries/readline/8.2.nix
+++ b/pkgs/development/libraries/readline/8.2.nix
@@ -3,7 +3,7 @@
 , updateAutotoolsGnuConfigScriptsHook
 , ncurses, termcap
 , curses-library ?
-    if stdenv.hostPlatform.isWindows
+    if stdenv.hostPlatform.isWindows && !stdenv.hostPlatform.isUnix
     then termcap
     else ncurses
 }:
@@ -35,13 +35,15 @@ stdenv.mkDerivation rec {
      in
        import ./readline-8.2-patches.nix patch);
 
+  hardeningDisable = lib.optionals stdenv.hostPlatform.isCygwin [ "fortify" ];
+
   patches = lib.optionals (curses-library.pname == "ncurses") [
     ./link-against-ncurses.patch
   ] ++ [
     ./no-arch_only-8.2.patch
   ]
   ++ upstreamPatches
-  ++ lib.optionals stdenv.hostPlatform.isWindows [
+  ++ lib.optionals (stdenv.hostPlatform.isWindows && !stdenv.hostPlatform.isUnix) [
     (fetchpatch {
       name = "0001-sigwinch.patch";
       url = "https://github.com/msys2/MINGW-packages/raw/90e7536e3b9c3af55c336d929cfcc32468b2f135/mingw-w64-readline/0001-sigwinch.patch";

From 8b47da26c80999a4ac32cb47427cc5cf2ffd8b02 Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:27:10 +0000
Subject: [PATCH 08/13] ncurses: disable fortify under Cygwin

---
 pkgs/development/libraries/ncurses/default.nix | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pkgs/development/libraries/ncurses/default.nix b/pkgs/development/libraries/ncurses/default.nix
index 0ee09d2416cd8..8dc98c70bdb83 100644
--- a/pkgs/development/libraries/ncurses/default.nix
+++ b/pkgs/development/libraries/ncurses/default.nix
@@ -99,6 +99,11 @@ stdenv.mkDerivation (finalAttrs: {
     CFLAGS=-D_XOPEN_SOURCE_EXTENDED
   '';
 
+  # Fortify currently breaks under the nixpkgs' Cygwin with errors such as:
+  #     two or more data types in declaration specifiers
+  #     conflicting types for 'read'
+  hardeningDisable = lib.optionals stdenv.hostPlatform.isCygwin [ "fortify" ];
+
   enableParallelBuilding = true;
 
   doCheck = false;

From 74bc0449269a80c546899d859e39089e9468bff2 Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:27:29 +0000
Subject: [PATCH 09/13] bash: fix compilation under Cygwin

---
 pkgs/shells/bash/5.nix | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/pkgs/shells/bash/5.nix b/pkgs/shells/bash/5.nix
index 1e1fe340dcda1..ae2c7742abc62 100644
--- a/pkgs/shells/bash/5.nix
+++ b/pkgs/shells/bash/5.nix
@@ -14,6 +14,7 @@
 , forFHSEnv ? false
 
 , pkgsStatic
+, ncurses
 }:
 
 let
@@ -36,7 +37,7 @@ stdenv.mkDerivation rec {
     # bionic libc is super weird and has issues with fortify outside of its own libc, check this comment:
     # https://github.com/NixOS/nixpkgs/pull/192630#discussion_r978985593
     # or you can check libc/include/sys/cdefs.h in bionic source code
-    ++ lib.optional (stdenv.hostPlatform.libc == "bionic") "fortify";
+    ++ lib.optional (stdenv.hostPlatform.libc == "bionic" || stdenv.hostPlatform.isCygwin) "fortify";
 
   outputs = [ "out" "dev" "man" "doc" "info" ];
 
@@ -84,10 +85,9 @@ stdenv.mkDerivation rec {
   ] ++ lib.optionals stdenv.hostPlatform.isCygwin [
     "--without-libintl-prefix"
     "--without-libiconv-prefix"
-    "--with-installed-readline"
+    "--with-curses"
     "bash_cv_dev_stdin=present"
     "bash_cv_dev_fd=standard"
-    "bash_cv_termcap_lib=libncurses"
   ] ++ lib.optionals (stdenv.hostPlatform.libc == "musl") [
     "--disable-nls"
   ] ++ lib.optionals stdenv.hostPlatform.isFreeBSD [
@@ -103,15 +103,10 @@ stdenv.mkDerivation rec {
     ++ lib.optional withDocs texinfo
     ++ lib.optional stdenv.hostPlatform.isDarwin stdenv.cc.bintools;
 
-  buildInputs = lib.optional interactive readline;
+  buildInputs = lib.optional interactive readline ++ lib.optionals stdenv.hostPlatform.isCygwin [ ncurses ];
 
   enableParallelBuilding = true;
 
-  makeFlags = lib.optionals stdenv.hostPlatform.isCygwin [
-    "LOCAL_LDFLAGS=-Wl,--export-all,--out-implib,libbash.dll.a"
-    "SHOBJ_LIBS=-lbash"
-  ];
-
   nativeCheckInputs = [ util-linux ];
   doCheck = false; # dependency cycle, needs to be interactive
 

From 3495b2eeff4953b68c05294f6a7a1a5a1c50b24c Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Fri, 8 Nov 2024 01:27:47 +0000
Subject: [PATCH 10/13] cygwin: include libcygwin1.dll in DLL search path

---
 pkgs/build-support/cc-wrapper/default.nix | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pkgs/build-support/cc-wrapper/default.nix b/pkgs/build-support/cc-wrapper/default.nix
index 085f64d37dd4b..8a0c9ab0787b9 100644
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/pkgs/build-support/cc-wrapper/default.nix
@@ -474,6 +474,7 @@ stdenvNoCC.mkDerivation {
         echo addToSearchPath "LINK_DLL_FOLDERS" "${cc_solib}/lib" > $out
         echo addToSearchPath "LINK_DLL_FOLDERS" "${cc_solib}/lib64" >> $out
         echo addToSearchPath "LINK_DLL_FOLDERS" "${cc_solib}/lib32" >> $out
+        echo addToSearchPath "LINK_DLL_FOLDERS" "${libc_bin}/bin" > $out
       '';
     });
 

From c0b60f38d17897cfc626e58215f1a4c0a85ef8fc Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Sat, 9 Nov 2024 09:19:30 +1100
Subject: [PATCH 11/13] bintools-wrapper: don't set fortify on Cygwin

The size of various things don't line up when enabling fortification.
This might be able to be fixed by looking at the Cywin builds, because
I think they don't generally disable fortify.
---
 pkgs/build-support/bintools-wrapper/default.nix | 2 ++
 pkgs/development/libraries/ncurses/default.nix  | 5 -----
 pkgs/development/libraries/readline/8.2.nix     | 2 --
 pkgs/shells/bash/5.nix                          | 2 +-
 4 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/pkgs/build-support/bintools-wrapper/default.nix b/pkgs/build-support/bintools-wrapper/default.nix
index a2a0736c2221b..5f9904162a0bf 100644
--- a/pkgs/build-support/bintools-wrapper/default.nix
+++ b/pkgs/build-support/bintools-wrapper/default.nix
@@ -39,8 +39,10 @@
 , defaultHardeningFlags ? [
     "bindnow"
     "format"
+  ] ++ lib.optionals (!stdenvNoCC.targetPlatform.isCygwin) [
     "fortify"
     "fortify3"
+  ] ++ [
     "pic"
     "relro"
     "stackprotector"
diff --git a/pkgs/development/libraries/ncurses/default.nix b/pkgs/development/libraries/ncurses/default.nix
index 8dc98c70bdb83..0ee09d2416cd8 100644
--- a/pkgs/development/libraries/ncurses/default.nix
+++ b/pkgs/development/libraries/ncurses/default.nix
@@ -99,11 +99,6 @@ stdenv.mkDerivation (finalAttrs: {
     CFLAGS=-D_XOPEN_SOURCE_EXTENDED
   '';
 
-  # Fortify currently breaks under the nixpkgs' Cygwin with errors such as:
-  #     two or more data types in declaration specifiers
-  #     conflicting types for 'read'
-  hardeningDisable = lib.optionals stdenv.hostPlatform.isCygwin [ "fortify" ];
-
   enableParallelBuilding = true;
 
   doCheck = false;
diff --git a/pkgs/development/libraries/readline/8.2.nix b/pkgs/development/libraries/readline/8.2.nix
index 40833dec2533d..4f85d75ad3256 100644
--- a/pkgs/development/libraries/readline/8.2.nix
+++ b/pkgs/development/libraries/readline/8.2.nix
@@ -35,8 +35,6 @@ stdenv.mkDerivation rec {
      in
        import ./readline-8.2-patches.nix patch);
 
-  hardeningDisable = lib.optionals stdenv.hostPlatform.isCygwin [ "fortify" ];
-
   patches = lib.optionals (curses-library.pname == "ncurses") [
     ./link-against-ncurses.patch
   ] ++ [
diff --git a/pkgs/shells/bash/5.nix b/pkgs/shells/bash/5.nix
index ae2c7742abc62..ecc0813551389 100644
--- a/pkgs/shells/bash/5.nix
+++ b/pkgs/shells/bash/5.nix
@@ -37,7 +37,7 @@ stdenv.mkDerivation rec {
     # bionic libc is super weird and has issues with fortify outside of its own libc, check this comment:
     # https://github.com/NixOS/nixpkgs/pull/192630#discussion_r978985593
     # or you can check libc/include/sys/cdefs.h in bionic source code
-    ++ lib.optional (stdenv.hostPlatform.libc == "bionic" || stdenv.hostPlatform.isCygwin) "fortify";
+    ++ lib.optional (stdenv.hostPlatform.libc == "bionic") "fortify";
 
   outputs = [ "out" "dev" "man" "doc" "info" ];
 

From 20d2d5b9931bc9a6e73120abebeda6076b569246 Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Sat, 9 Nov 2024 09:21:17 +1100
Subject: [PATCH 12/13] bash: set empty makeFlags to avoid mass rebuild

---
 pkgs/shells/bash/5.nix | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pkgs/shells/bash/5.nix b/pkgs/shells/bash/5.nix
index ecc0813551389..860dd64362595 100644
--- a/pkgs/shells/bash/5.nix
+++ b/pkgs/shells/bash/5.nix
@@ -107,6 +107,8 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  makeFlags = [ ];
+
   nativeCheckInputs = [ util-linux ];
   doCheck = false; # dependency cycle, needs to be interactive
 

From 573c420de7c44b44e49981edf2b80aafae17756e Mon Sep 17 00:00:00 2001
From: Brian McKenna <brian@brianmckenna.org>
Date: Sat, 9 Nov 2024 09:21:38 +1100
Subject: [PATCH 13/13] mingw-w64: allow Cygwin as a crt

---
 pkgs/os-specific/windows/mingw-w64/default.nix | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pkgs/os-specific/windows/mingw-w64/default.nix b/pkgs/os-specific/windows/mingw-w64/default.nix
index d490debcebb0f..684d4bd3efeeb 100644
--- a/pkgs/os-specific/windows/mingw-w64/default.nix
+++ b/pkgs/os-specific/windows/mingw-w64/default.nix
@@ -10,6 +10,7 @@
 assert lib.assertOneOf "crt" crt [
   "msvcrt"
   "ucrt"
+  "cygwin"
 ];
 
 stdenv.mkDerivation {