fix gemspec directive support (closes #2)

Readme.md

@@ -110,6 +110,22 @@ gemfileEnv {
 };
 ```
 
+**"gems4nix: Gemfile uses the `gemspec` directive but no gemspec was supplied"**
+Your Gemfile calls `gemspec` (the default `bundle gem` layout). Group inference
+runs Bundler against a sandboxed Gemfile, so the `.gemspec` — and anything it
+`require_relative`s — must be handed to `gemfileEnv` explicitly:
+```nix
+gemfileEnv {
+  # ...
+  gemspec    = ./my-gem.gemspec;
+  extraFiles = {
+    "lib/my_gem/version.rb" = ./lib/my_gem/version.rb;
+  };
+};
+```
+Alternatively, pass an explicit `gemGroups = { name = [ "default" ]; ... }`
+mapping to skip Bundler group inference entirely.
+
 ## How It Works
 
 The pipeline has three stages:

flake.nix

@@ -2,7 +2,7 @@
   description = "Bundle Ruby gems into an environment, using Bundler checksums";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs?ref=24.11";
+    nixpkgs.url = "github:NixOS/nixpkgs?ref=26.05";
   };
 
   outputs =
@@ -58,6 +58,17 @@
             gemfileLock = ./test/integration/platform-gems/Gemfile.lock;
             groups = [ "default" ];
           };
+
+          gemspecDirectiveGems = gemfileEnv {
+            name = "gemspec-directive-test";
+            gemfile = ./test/integration/gemspec-directive/Gemfile;
+            gemfileLock = ./test/integration/gemspec-directive/Gemfile.lock;
+            gemspec = ./test/integration/gemspec-directive/foo.gemspec;
+            extraFiles = {
+              "lib/foo/version.rb" = ./test/integration/gemspec-directive/lib/foo/version.rb;
+            };
+            groups = [ "default" ];
+          };
         in
         {
           unit-resolve = nixEvalCheck "resolve" ./test/unit/test-resolve-logic.nix;
@@ -76,6 +87,19 @@
                 ruby ${./test/integration/platform-gems/validate.rb}
                 touch $out
               '';
+
+          integration-gemspec-directive =
+            pkgs.runCommand "integration-gemspec-directive"
+              {
+                buildInputs = [
+                  pkgs.ruby
+                  gemspecDirectiveGems
+                ];
+              }
+              ''
+                ruby ${./test/integration/gemspec-directive/validate.rb}
+                touch $out
+              '';
         }
       );
 

lib/gemfile-env/default.nix

@@ -30,6 +30,8 @@ in
     "test"
   ],
   gemGroups ? null, # null = auto-detect via gem-groups.rb IFD; attrset = override
+  gemspec ? null, # path to *.gemspec when the Gemfile uses the `gemspec` directive
+  extraFiles ? { }, # { "relative/dest" = ./src; } — files the gemspec require_relatives
   gemConfig ? defaultGemConfig,
   ruby ? defaultRuby,
   debug ? false, # when true, builtins.trace each gem being built
@@ -39,7 +41,15 @@ let
 
   # ── parsing ──────────────────────────────────────────────────
   parseGemfileAndLockfile = callPackage ./parse-gemfile-and-lockfile.nix { };
-  parsed = parseGemfileAndLockfile { inherit gemfile gemfileLock gemGroups; };
+  parsed = parseGemfileAndLockfile {
+    inherit
+      gemfile
+      gemfileLock
+      gemGroups
+      gemspec
+      extraFiles
+      ;
+  };
   gemMetadata = parsed.gems;
   depGraph = parsed.depGraph;
 

lib/gemfile-env/parse-gemfile-and-lockfile.nix

@@ -29,6 +29,7 @@
   runCommand,
   ruby,
   bundler,
+  git,
   fetchurl,
   stdenv,
   defaultGemConfig,
@@ -42,6 +43,8 @@
   gemfile,
   gemfileLock,
   gemGroups ? null, # null = auto-detect via gem-groups.rb; attrset = override
+  gemspec ? null, # path to *.gemspec when the Gemfile uses the `gemspec` directive
+  extraFiles ? { }, # { "relative/dest" = ./src; } — files the gemspec require_relatives
 }:
 
 let
@@ -56,21 +59,69 @@ let
 
   # ── IO ───────────────────────────────────────────────────────
 
+  # Detect the Bundler `gemspec` directive in the Gemfile. When present, the
+  # group-detection IFD sandbox must include the gemspec (and anything it
+  # require_relatives) or Bundler aborts with `Bundler::InvalidOption: There
+  # are no gemspecs`. See github.com/omc/gems4nix issue #2.
+  gemfileText = builtins.readFile gemfile;
+  gemfileUsesGemspec =
+    let
+      isGemspecLine = line: builtins.match "[[:space:]]*gemspec([[:space:]#(].*)?" line != null;
+    in
+    lib.any isGemspecLine (lib.splitString "\n" gemfileText);
+
+  needsGemspecButMissing = gemfileUsesGemspec && gemspec == null && gemGroups == null;
+
+  gemspecError = throw ''
+    gems4nix: Gemfile uses the `gemspec` directive but no gemspec was supplied.
+
+    Bundler needs the .gemspec (and any files it require_relatives) available
+    at group-detection time. Add these arguments to your gemfileEnv call:
+
+        gemspec    = ./<your-name>.gemspec;
+        extraFiles = { "lib/<your-name>/version.rb" = ./lib/<your-name>/version.rb; };
+
+    Alternatively, pass an explicit `gemGroups = { ... }` mapping to skip
+    Bundler group inference entirely.
+  '';
+
+  # Copy the caller-supplied gemspec into the sandbox as `project.gemspec`.
+  # The filename doesn't matter to Bundler — it globs `*.gemspec` — but the
+  # gemspec's require_relative calls resolve from the sandbox root, so
+  # extraFiles must land at their declared destinations.
+  copyGemspecCmd = lib.optionalString (gemspec != null) ''
+    cp ${gemspec} project.gemspec
+  '';
+
+  copyExtraFilesCmd = lib.concatMapStringsSep "\n" (dest: ''
+    mkdir -p "$(dirname ${lib.escapeShellArg dest})"
+    cp ${extraFiles.${dest}} ${lib.escapeShellArg dest}
+  '') (builtins.attrNames extraFiles);
+
   # use the Gemfile to produce group information for each gem
   # (skipped when the caller supplies an explicit gemGroups override)
   gemGroupsJson =
-    runCommand "gem-groups-json"
-      {
-        buildInputs = [
-          ruby
-          bundler
-        ];
-      }
-      ''
-        cp ${gemfile} Gemfile
-        cp ${gemfileLock} Gemfile.lock
-        ruby ${./gem-groups.rb} > $out
-      '';
+    if needsGemspecButMissing then
+      gemspecError
+    else
+      runCommand "gem-groups-json"
+        {
+          # git is needed because the canonical `bundle gem` gemspec computes
+          # spec.files via `IO.popen(%w[git ls-files -z])`. Without git on PATH
+          # that popen raises Errno::ENOENT and gemspec evaluation aborts.
+          buildInputs = [
+            ruby
+            bundler
+            git
+          ];
+        }
+        ''
+          cp ${gemfile} Gemfile
+          cp ${gemfileLock} Gemfile.lock
+          ${copyGemspecCmd}
+          ${copyExtraFilesCmd}
+          ruby ${./gem-groups.rb} > $out
+        '';
 
   # ── pure assembly (delegated to helpers) ─────────────────────
 

test/integration/gemspec-directive/Gemfile

@@ -0,0 +1,7 @@
+source "https://rubygems.org"
+
+gemspec
+
+group :test do
+  gem "rspec", "~> 3.0"
+end

test/integration/gemspec-directive/Gemfile.lock

@@ -0,0 +1,46 @@
+PATH
+  remote: .
+  specs:
+    foo (0.1.0)
+      rake (~> 13.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    diff-lcs (1.6.2)
+    rake (13.4.2)
+    rspec (3.13.2)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.6)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.5)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.8)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.7)
+
+PLATFORMS
+  arm64-darwin-25
+  ruby
+  universal-darwin
+
+DEPENDENCIES
+  foo!
+  rspec (~> 3.0)
+
+CHECKSUMS
+  diff-lcs (1.6.2) sha256=9ae0d2cba7d4df3075fe8cd8602a8604993efc0dfa934cff568969efb1909962
+  foo (0.1.0)
+  rake (13.4.2) sha256=cb825b2bd5f1f8e91ca37bddb4b9aaf345551b4731da62949be002fa89283701
+  rspec (3.13.2) sha256=206284a08ad798e61f86d7ca3e376718d52c0bc944626b2349266f239f820587
+  rspec-core (3.13.6) sha256=a8823c6411667b60a8bca135364351dda34cd55e44ff94c4be4633b37d828b2d
+  rspec-expectations (3.13.5) sha256=33a4d3a1d95060aea4c94e9f237030a8f9eae5615e9bd85718fe3a09e4b58836
+  rspec-mocks (3.13.8) sha256=086ad3d3d17533f4237643de0b5c42f04b66348c28bf6b9c2d3f4a3b01af1d47
+  rspec-support (3.13.7) sha256=0640e5570872aafefd79867901deeeeb40b0c9875a36b983d85f54fb7381c47c
+
+BUNDLED WITH
+   2.7.2

test/integration/gemspec-directive/foo.gemspec

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require_relative "lib/foo/version"
+
+Gem::Specification.new do |spec|
+  spec.name    = "foo"
+  spec.version = Foo::VERSION
+  spec.authors = ["gems4nix test"]
+  spec.summary = "Fixture exercising the `gemspec` directive"
+  spec.files   = ["lib/foo/version.rb"]
+  spec.required_ruby_version = ">= 3.0.0"
+
+  spec.add_dependency "rake", "~> 13.0"
+end

test/integration/gemspec-directive/lib/foo/version.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+module Foo
+  VERSION = "0.1.0"
+end

test/integration/gemspec-directive/validate.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+# Verifies group inference succeeds against a Gemfile using the `gemspec`
+# directive (default `bundle gem` layout). See github.com/omc/gems4nix
+# issue #2. The regression is that the group-detection IFD sandbox
+# previously omitted the gemspec, so Bundler aborted before any gems
+# could be resolved.
+
+require "rake"
+
+unless defined?(Rake::VERSION)
+  warn "expected Rake constant to be defined after require"
+  exit 1
+end
+
+puts "gemspec-directive: rake #{Rake::VERSION} loaded from #{Rake.method(:application).source_location.first}"