From eaf1c3ff300ab0b38ede67ac44aa95ec7c46ef45 Mon Sep 17 00:00:00 2001
From: Avimitin <dev@avimit.in>
Date: Sun, 27 Oct 2024 00:44:15 +0800
Subject: [PATCH] [nix] clean up impure env

Yesterday I reviewed my nix code and found that this ugly part can be
immediately improved. These env should not have top level binding and
evaluate with empty value everytime if "--impure" does not supply.
There should be value bind to them when they get evaluated, or they
should never exist in our nixpkgs namespace.

Signed-off-by: Avimitin <dev@avimit.in>
---
 nix/overlay.nix          |  8 ++------
 nix/pkgs/vcs-fhs-env.nix | 27 ++++++++++++++++++---------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/nix/overlay.nix b/nix/overlay.nix
index d6c81428b..522cb87db 100644
--- a/nix/overlay.nix
+++ b/nix/overlay.nix
@@ -27,12 +27,8 @@ rec {
   circt-full = final.callPackage ./pkgs/circt-full.nix { };
   rvv-codegen = final.callPackage ./pkgs/rvv-codegen.nix { };
   add-determinism = final.callPackage ./pkgs/add-determinism { }; # faster strip-undetereminism
-  # Using VCS need to set VC_STATIC_HOME and SNPSLMD_LICENSE_FILE to impure env, and add sandbox dir to VC_STATIC_HOME
-  vcStaticHome = builtins.getEnv "VC_STATIC_HOME";
-  snpslmdLicenseFile = builtins.getEnv "SNPSLMD_LICENSE_FILE";
-  vcs-fhs-env = assert final.lib.assertMsg (final.vcStaticHome != "") "No $VC_STATIC_HOME or '--impure' applied";
-    assert final.lib.assertMsg (final.snpslmdLicenseFile != "") "No $SNPSLMD_LICENSE_FILE or '--impure' applied";
-    final.callPackage ./pkgs/vcs-fhs-env.nix { };
+
+  vcs-fhs-env = final.callPackage ./pkgs/vcs-fhs-env.nix { };
 
   mill = let jre = final.jdk21; in
     (prev.mill.override { inherit jre; }).overrideAttrs (_: {
diff --git a/nix/pkgs/vcs-fhs-env.nix b/nix/pkgs/vcs-fhs-env.nix
index a9becb664..cf6329192 100644
--- a/nix/pkgs/vcs-fhs-env.nix
+++ b/nix/pkgs/vcs-fhs-env.nix
@@ -4,28 +4,37 @@
 #
 # For convenience, we still use the nixpkgs defined in flake to "callPackage" this derivation.
 # But the buildFHSEnv, targetPkgs is still from the locked nixpkgs.
-{ vcStaticHome
-, snpslmdLicenseFile
-, fetchFromGitHub
-}:
+{ lib, fetchFromGitHub }:
 let
   nixpkgsSrcs = fetchFromGitHub {
     owner = "NixOS";
     repo = "nixpkgs";
-    "rev" = "574d1eac1c200690e27b8eb4e24887f8df7ac27c";
-    "hash" = "sha256-v3rIhsJBOMLR8e/RNWxr828tB+WywYIoajrZKFM+0Gg=";
+    rev = "574d1eac1c200690e27b8eb4e24887f8df7ac27c";
+    hash = "sha256-v3rIhsJBOMLR8e/RNWxr828tB+WywYIoajrZKFM+0Gg=";
   };
 
   # The vcs we have only support x86-64_linux
   lockedPkgs = import nixpkgsSrcs { system = "x86_64-linux"; };
+
+  getEnv' = key:
+    let
+      val = builtins.getEnv key;
+    in
+    if val == "" then
+      builtins.throw "${key} not set or '--impure' not applied"
+    else val;
+
+  # Using VCS need to set VC_STATIC_HOME and SNPSLMD_LICENSE_FILE to impure env, and add sandbox dir to VC_STATIC_HOME
+  vcStaticHome = getEnv' "VC_STATIC_HOME";
+  snpslmdLicenseFile = getEnv' "SNPSLMD_LICENSE_FILE";
 in
 lockedPkgs.buildFHSEnv {
   name = "vcs-fhs-env";
 
   profile = ''
-    [ ! -e "${vcStaticHome}"  ] && echo "env VC_STATIC_HOME not set" && exit 1
-    [ ! -d "${vcStaticHome}"  ] && echo "VC_STATIC_HOME not accessible" && exit 1
-    [ -z "${snpslmdLicenseFile}"  ] && echo "env SNPS LICENSE not set" && exit 1
+    [ ! -e "${vcStaticHome}"  ] && echo "env VC_STATIC_HOME='${vcStaticHome}' points to unknown location" && exit 1
+    [ ! -d "${vcStaticHome}"  ] && echo "VC_STATIC_HOME='${vcStaticHome}' not accessible" && exit 1
+
     export VC_STATIC_HOME=${vcStaticHome}
 
     export TCL_TZ=UTC