Render headers as their own derivation

src/headers.nix

@@ -0,0 +1,63 @@
+{
+  lib,
+
+  src,
+  version,
+  nameSuffix,
+
+  stdenv,
+
+  unzip,
+  tcl,
+  zlib,
+  icu,
+
+  features ? { },
+  featureFlags ? [ ],
+
+  ...
+}:
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "sqlite-amalgamation${nameSuffix}";
+  inherit version src;
+
+  nativeBuildInputs = [
+    unzip
+    tcl
+  ];
+
+  buildInputs = [
+    zlib
+  ] ++ lib.optional features.ENABLE_ICU [
+    icu
+  ];
+
+  # required for aarch64 but applied for all arches for simplicity
+  preConfigure = ''
+    patchShebangs configure
+  '';
+
+  # sqlite relies on autosetup now; so many of the
+  # previously-understood flags are gone. They should instead be set
+  # on a per-output basis.
+  setOutputFlags = false;
+
+  configureFlags = lib.optional features.ENABLE_ICU [
+    "--enable-icu-collations"
+    "--with-icu-config=${lib.getExe' icu.dev "icu-config"}"
+  ];
+
+  env.NIX_CFLAGS_COMPILE = lib.concatStringsSep " " featureFlags;
+  env.NIX_CFLAGS_LINK = lib.optionalString features.ENABLE_FTS5 "-lm";
+
+  makeFlags = [ "sqlite3.h" ];
+
+  installPhase = ''
+    runHook preInstall
+
+    install -Dm444 sqlite3.h src/sqlite3ext.h -t "$out/include"
+
+    runHook postInstall
+  '';
+})

src/mk-sqlite.nix

@@ -63,6 +63,15 @@ let
     (x: if x == "" then "" else "-${x}")
   ];
 
+  headers = pkgs.callPackage ./headers.nix ({
+    inherit version src;
+    inherit amalgamate;
+    inherit features;
+    inherit extensions;
+    inherit extraLibraries;
+    nameSuffix = suffix;
+  } // config);
+
   coreInitExt = if extensions == [ ]
     then null
     else pkgs.callPackage ./core-init-ext.nix ({
@@ -76,6 +85,8 @@ in {
   _suffix = suffix;
   _coreInitExt = coreInitExt;
 
+  inherit headers;
+
   sqlite = pkgs.callPackage ./sqlite.nix ({
     inherit version src;
     inherit amalgamate;