add missing mainPackage attr in the config for the ghci runner

lib/default.nix

@@ -118,6 +118,11 @@ let
   else o
   ;
 
+  cabalDepPackage = dep:
+  if isAttrs dep
+  then dep.name
+  else dep;
+
 in {
   inherit
   flake-utils
@@ -148,6 +153,7 @@ in {
   empty
   evalModules
   overridesVia
+  cabalDepPackage
   ;
 
   ghcOverlay = import ./ghc-overlay.nix;

lib/with-config.nix

@@ -53,6 +53,7 @@ let
     # - restarts
     # - cwd
     ghci = {
+      mainPackage = config.main;
       inherit packages;
       setup = config.ghci.setup;
       run = config.ghci.run;

modules/basic.nix

@@ -9,18 +9,36 @@ let
   cabalOptionsModule = import ./cabal-options.nix { inherit global util; };
 
   baseFromPackages = let
-    pkg = head (attrValues config.internal.packagePaths);
+    paths = attrValues config.internal.packagePaths;
+    pkg = head paths;
     next = p:
       if p == "/"
-      then throw "Could not determine base dir: Invalid package path ${pkg}"
+      then throw "Could not determine project root dir: Invalid package path ${pkg}"
       else if isStorePath p || pathExists "${p}/flake.nix"
       then p
       else next (dirOf p);
   in
-   if length (attrNames config.internal.packagePaths) == 0
-   then throw "You have to specify either the 'base' option, pointing to the project root, or an entry in [](#opt-general-packages)."
+   if length paths == 0
+   then throw ''
+   Could not determine project root dir.
+   Either specify `base = ./.;` or add entries to `packages`.
+   See https://tryp.io/hix/index.html#packages for more.
+   ''
    else next pkg;
 
+   autoMain = let
+     ps = attrValues config.packages;
+
+    inDeps = target: thing: any (dep: util.cabalDepPackage dep == target) thing.dependencies;
+
+    hasDepOn = dep: pkg:
+    pkg.name != dep &&
+    any (inDeps dep) (attrValues pkg.internal.componentsSet);
+
+     isNoDep = pkg: ! (any (hasDepOn pkg.name) ps);
+
+    in findFirst isNoDep null (attrValues config.packages);
+
 in {
   options = {
 
@@ -40,7 +58,6 @@ in {
       description = mdDoc ''
       The project's Cabal packages, with Cabal package names as keys and package config as values.
       The config is processed with [HPack](https://github.com/sol/hpack).
-      Consult the docs for the package options to learn how this is translated.
       '';
       example = literalExpression ''
       {
@@ -57,6 +74,8 @@ in {
         The name of a key in `packages` that is considered to be the main package.
         This package will be assigned to the `defaultPackage` flake output that is built by a plain
         `nix build`.
+        If this option is undefined, Hix will choose one of the packages that are not in the dependencies of any other
+        package.
       '';
       type = str;
     };
@@ -250,12 +269,29 @@ in {
   config = {
     base = mkDefault baseFromPackages;
 
-    main = mkDefault (
-      if (length config.internal.packageNames == 1)
-      then head config.internal.packageNames
+    main = mkDefault (let
+      names = config.internal.packageNames;
+      count = length names;
+    in
+      if count == 1
+      then head names
+      else if count == 0
+      then ''
+      This action requires at least one package to be defined, as in:
+      {
+        packages.my-project = { src = ./.; };
+      }
+      ''
+      else if autoMain != null
+      then autoMain.name
       else throw ''
-      The config option 'main' must name one of the 'packages' if more than one is defined.
-      See https://tryp.io/hix/index.html#opt-general-main
+      Could not determine the main package.
+      This should only happen if all packages depend on each other cyclically.
+      If that is not the case, please report a bug at: https://github.com/tek/hix/issues
+      You can specify the main package explicitly:
+      {
+        main = "my-package";
+      }
       ''
     );
 

modules/package.nix

@@ -11,8 +11,10 @@ let
 
   anyEnabled = set: any (a: a.enable) (attrValues set);
 
+  # excludes `pkgConfig.executable` because it's used to determine whether the default executable should be enabled.
   hasComponents =
-    pkgConfig.library.enable || anyEnabled pkgConfig.executables ||
+    pkgConfig.library.enable || anyEnabled pkgConfig.libraries ||
+    anyEnabled pkgConfig.executables ||
     pkgConfig.test.enable || anyEnabled pkgConfig.tests ||
     pkgConfig.benchmark.enable || anyEnabled pkgConfig.benchmarks;
 
@@ -73,13 +75,13 @@ let
 
     };
 
-    config = optionalAttrs default {
-      enable = mkDefault (!hasComponents);
-    } // {
-      dependencies = optional (config.dependOnLibrary && pkgConfig.library.enable) pkgName;
-
-      ghc-options = mkIf (sort != "benchmark") config.ghc-options-exe;
-    };
+    config =
+      optionalAttrs default { enable = mkDefault (!hasComponents); }
+      //
+      {
+        dependencies = optional (config.dependOnLibrary && pkgConfig.library.enable) pkgName;
+        ghc-options = mkIf (sort != "benchmark") config.ghc-options-exe;
+      };
 
   };
 
@@ -115,9 +117,10 @@ in {
   options = with types; {
 
     name = mkOption {
-      description = mdDoc "The name of the package, defaulting to the attribute name in the config.";
+      description = mdDoc "The name of the package, determined by the attribute name in the config.";
       type = str;
       default = name;
+      readOnly = true;
     };
 
     src = mkOption {
@@ -135,7 +138,13 @@ in {
     };
 
     libraries = mkOption {
-      description = mdDoc "";
+      description = mdDoc ''
+      The sublibraries of this package.
+      Unlike [](#opt-package-library), these are treated specially by cabal.
+      To depend on them, use `<pkg>:<lib>`.
+      If [](#opt-package-libraries._name_.public) is set to `false`, you can only depend on them from other components
+      in the same package (this is then called an internal library – default is `true`).
+      '';
       type = attrsOf (libSubmodule false);
       default = {};
     };
@@ -352,6 +361,7 @@ in {
 
     internal.componentsSet =
       optionalAttrs config.library.enable { library = config.library; } //
+      config.libraries //
       optionalAttrs config.executable.enable { ${config.executable.name} = config.executable; } //
       config.executables //
       optionalAttrs config.test.enable { ${config.test.name} = config.test; } //

test/default.nix

@@ -8,6 +8,7 @@ let
     basic = test "basic";
     deps = test "deps";
     ghci = test "ghci";
+    ghci-vm = test "ghci-vm";
     packages = test "packages";
     hackage = test "hackage";
     cross = test "cross";
@@ -28,7 +29,7 @@ let
 
   testsA = concatStringsSep " " (mapAttrsToList testA tests);
 
-  ciSkipTests = "ghci service postgres hackage";
+  ciSkipTests = "ghci-vm service postgres hackage";
 
 in {
   main = pkgs.writeScript "hix-tests" ''

test/ghci-vm/root/cabal.project

@@ -0,0 +1 @@
+packages: .

test/ghci-vm/root/flake.nix

@@ -0,0 +1,26 @@
+{
+  description = "hix test project";
+
+  inputs.hix.url = "path:HIX";
+
+  outputs = { hix, ... }: hix.lib.flake ({config, ...}: {
+    packages.root = {
+      src = ./pkg;
+      library.enable = true;
+      library.dependencies = ["http-client" "bytestring" "path" "path-io"];
+      library.default-extensions = ["OverloadedStrings"];
+      executable.enable = true;
+      test.enable = true;
+      test.env = "hix-ghci-test";
+    };
+    envs.hix-ghci-test.services.test.enable = true;
+    services.test = {
+      nixos.services.nginx = {
+        enable = true;
+        virtualHosts.localhost.locations."/test".return = "200 test-endpoint";
+      };
+      ports.nginx = { host = 2; guest = 80; };
+    };
+    internal.hixCli.dev = true;
+  });
+}

test/ghci-vm/root/pkg/app/Main.hs

@@ -0,0 +1,7 @@
+module Main where
+
+import Root.Lib (string)
+
+main :: IO ()
+main =
+  putStrLn string

test/ghci-vm/root/pkg/lib/Root/Lib.hs

@@ -0,0 +1,25 @@
+module Root.Lib where
+
+import Control.Exception
+import Control.Concurrent
+import qualified Data.ByteString.Lazy.Char8 as ByteString
+import Network.HTTP.Client
+
+tryRequest :: Manager -> IO (Response ByteString.ByteString)
+tryRequest man =
+  spin 10
+  where
+    spin 0 = req
+    spin n = catch req (err n)
+    err :: Int -> SomeException -> IO (Response ByteString.ByteString)
+    err n _ = do
+      threadDelay 1000000
+      spin (n - 1)
+    req =
+      httpLbs "http://localhost:20002/test" man
+
+test :: IO ()
+test = do
+  man <- newManager defaultManagerSettings
+  res <- tryRequest man
+  ByteString.putStrLn (responseBody res)

test/ghci-vm/root/pkg/test/Main.hs

@@ -0,0 +1,6 @@
+module Main where
+
+import Root.Lib (test)
+
+main :: IO ()
+main = test

test/ghci-vm/test.nix

@@ -0,0 +1,12 @@
+{ pkgs }:
+{
+  test = builtins.toFile "ghci-vm-test" ''
+    cd ./root
+    nix flake update
+    nix run .#gen-cabal
+
+    ghci_match '.#ghci -- -p root -t main' 'test-endpoint' "ghci service output with component env does not contain 'test-endpoint'"
+
+    ghci_match '.#env.hix-ghci-test.ghci -- -t main' 'test-endpoint' "ghci service output with explicit env does not contain 'test-endpoint'"
+  '';
+}

test/ghci/root/core/lib/Root/Lib.hs

@@ -0,0 +1,4 @@
+module Root.Lib where
+
+test :: IO ()
+test = putStrLn "core-lib-test"

test/ghci/root/flake.nix

@@ -1,25 +1,22 @@
 {
   description = "hix test project";
 
-  inputs.hix.url = path:HIX;
+  inputs.hix.url = "path:HIX";
 
   outputs = { hix, ... }: hix.lib.flake ({config, ...}: {
-    packages.root = {
-      src = ./pkg;
-      library.enable = true;
-      library.dependencies = ["http-client" "bytestring" "path" "path-io"];
-      library.default-extensions = ["OverloadedStrings"];
-      executable.enable = true;
-      test.enable = true;
-      test.env = "hix-ghci-test";
-    };
-    envs.hix-ghci-test.services.test.enable = true;
-    services.test = {
-      nixos.services.nginx = {
-        enable = true;
-        virtualHosts.localhost.locations."/test".return = "200 test-endpoint";
+    packages = {
+      core = {
+        src = ./core;
+        library.enable = true;
+      };
+      root = {
+        src = ./pkg;
+        library.enable = true;
+        executable.enable = true;
+        test.enable = true;
+        library.dependencies = ["path" "path-io" "core"];
+        # library.default-extensions = ["OverloadedStrings"];
       };
-      ports.nginx = { host = 2; guest = 80; };
     };
     ghci.run.print = ''putStrLn "print success"'';
     ghci.run.cwd = ''putStrLn . toFilePath =<< getCurrentDir'';

test/ghci/root/pkg/app/Main.hs

@@ -1,7 +1,4 @@
 module Main where
 
-import Root.Lib (string)
-
 main :: IO ()
-main =
-  putStrLn string
+main = putStrLn "app-main"

test/ghci/root/pkg/lib/Root/Lib.hs

@@ -1,25 +1,4 @@
 module Root.Lib where
 
-import Control.Exception
-import Control.Concurrent
-import qualified Data.ByteString.Lazy.Char8 as ByteString
-import Network.HTTP.Client
-
-tryRequest :: Manager -> IO (Response ByteString.ByteString)
-tryRequest man =
-  spin 10
-  where
-    spin 0 = req
-    spin n = catch req (err n)
-    err :: Int -> SomeException -> IO (Response ByteString.ByteString)
-    err n _ = do
-      threadDelay 1000000
-      spin (n - 1)
-    req =
-      httpLbs "http://localhost:20002/test" man
-
 test :: IO ()
-test = do
-  man <- newManager defaultManagerSettings
-  res <- tryRequest man
-  ByteString.putStrLn (responseBody res)
+test = putStrLn "lib-test"

test/ghci/test.nix

@@ -11,10 +11,6 @@
 
     ghci_match '.#ghci -- -p root -c lib -m Root.Lib -r print' 'print success' "ghci output for 'print' runner does not contain 'print success'"
 
-    ghci_match '.#ghci -- -p root -t main' 'test-endpoint' "ghci service output with component env does not contain 'test-endpoint'"
-
-    ghci_match '.#env.hix-ghci-test.ghci -- -t main' 'test-endpoint' "ghci service output with explicit env does not contain 'test-endpoint'"
-
     ghci_match '.#ghci-app' 'print success' "ghci-app did not output 'print success'"
   '';
 }