stdenv.mkDerivation: support mainProgram as a top‐level attribute

lib/meta.nix

@@ -402,7 +402,7 @@ rec {
     licstr: default: lowercaseLicenses.${lib.toLower licstr} or default;
 
   /**
-    Get the path to the main program of a package based on meta.mainProgram
+    Get the path to the main program of a package based on `mainProgram`.
 
     # Inputs
 
@@ -432,12 +432,12 @@ rec {
   getExe =
     x:
     getExe' x (
-      x.meta.mainProgram or (
+      x.mainProgram or x.meta.mainProgram or (
         # This could be turned into an error when 23.05 is at end of life
         lib.warn
           "getExe: Package ${
             lib.strings.escapeNixIdentifier x.meta.name or x.pname or x.name
-          } does not have the meta.mainProgram attribute. We'll assume that the main program has the same name for now, but this behavior is deprecated, because it leads to surprising errors when the assumption does not hold. If the package has a main program, please set `meta.mainProgram` in its definition to make this warning go away. Otherwise, if the package does not have a main program, or if you don't control its definition, use getExe' to specify the name to the program, such as lib.getExe' foo \"bar\"."
+          } does not have the mainProgram attribute. We'll assume that the main program has the same name for now, but this behavior is deprecated, because it leads to surprising errors when the assumption does not hold. If the package has a main program, please set `mainProgram` in its definition to make this warning go away. Otherwise, if the package does not have a main program, or if you don't control its definition, use getExe' to specify the name to the program, such as lib.getExe' foo \"bar\"."
           lib.getName
           x
       )

lib/tests/misc.nix

@@ -4082,6 +4082,16 @@ runTests {
   };
 
   testGetExeOutput = {
+    expr = getExe {
+      type = "derivation";
+      out = "somelonghash";
+      bin = "somelonghash";
+      mainProgram = "mainProgram";
+    };
+    expected = "somelonghash/bin/mainProgram";
+  };
+
+  testGetExeOutputMeta = {
     expr = getExe {
       type = "derivation";
       out = "somelonghash";

pkgs/by-name/he/hello/package.nix

@@ -34,7 +34,7 @@ stdenv.mkDerivation (finalAttrs: {
 
   # Give hello some install checks for testing purpose.
   postInstallCheck = ''
-    stat "''${!outputBin}/bin/${finalAttrs.meta.mainProgram}"
+    stat "''${!outputBin}/bin/${finalAttrs.mainProgram}"
   '';
 
   passthru.tests = {
@@ -43,6 +43,8 @@ stdenv.mkDerivation (finalAttrs: {
 
   passthru.tests.run = callPackage ./test.nix { hello = finalAttrs.finalPackage; };
 
+  mainProgram = "hello";
+
   meta = {
     description = "Program that produces a familiar, friendly greeting";
     longDescription = ''
@@ -53,7 +55,6 @@ stdenv.mkDerivation (finalAttrs: {
     changelog = "https://git.savannah.gnu.org/cgit/hello.git/plain/NEWS?h=v${finalAttrs.version}";
     license = lib.licenses.gpl3Plus;
     maintainers = with lib.maintainers; [ stv0g ];
-    mainProgram = "hello";
     platforms = lib.platforms.all;
   };
 })

pkgs/by-name/ve/versionCheckHook/hook.sh

@@ -40,19 +40,19 @@ versionCheckHook(){
     local cmdProgram cmdArg echoPrefix
     if [[ ! -z "${versionCheckProgram-}" ]]; then
         cmdProgram="$versionCheckProgram"
-    elif [[ ! -z "${NIX_MAIN_PROGRAM-}" ]]; then
-        cmdProgram="${!outputBin}/bin/${NIX_MAIN_PROGRAM}"
+    elif [[ ! -z "${mainProgram-}" ]]; then
+        cmdProgram="${!outputBin}/bin/${mainProgram}"
     elif [[ ! -z "${pname-}" ]]; then
-        echo "versionCheckHook: Package \`${pname}\` does not have the \`meta.mainProgram\` attribute." \
+        echo "versionCheckHook: Package \`${pname}\` does not have the \`mainProgram\` attribute." \
             "We'll assume that the main program has the same name for now, but this behavior is deprecated," \
             "because it leads to surprising errors when the assumption does not hold." \
-            "If the package has a main program, please set \`meta.mainProgram\` in its definition to make this warning go away." \
+            "If the package has a main program, please set \`mainProgram\` in its definition to make this warning go away." \
             "Should the binary that outputs the intended version differ from \`meta.mainProgram\`, consider setting \`versionCheckProgram\` instead." >&2
         cmdProgram="${!outputBin}/bin/${pname}"
     else
-        echo "versionCheckHook: \$NIX_MAIN_PROGRAM, \$versionCheckProgram and \$pname are all empty, so" \
+        echo "versionCheckHook: \$mainProgram, \$versionCheckProgram and \$pname are all empty, so" \
             "we don't know how to run the versionCheckPhase." \
-            "To fix this, set one of \`meta.mainProgram\` or \`versionCheckProgram\`." >&2
+            "To fix this, set one of \`mainProgram\` or \`versionCheckProgram\`." >&2
         exit 2
     fi
 

pkgs/stdenv/generic/check-meta.nix

@@ -605,6 +605,14 @@ let
       ]
       ++ optional (hasOutput "man") "man";
     }
+    // optionalAttrs (attrs ? mainProgram) {
+      # This is used within derivations, but is also useful metadata
+      # for external consumers.
+      #
+      # TODO: Phase out setting this in `meta` (but still keep
+      # inheriting it here).
+      inherit (attrs) mainProgram;
+    }
     // (filterAttrs (_: v: v != null) {
       # CI scripts look at these to determine pings. Note that we should filter nulls out of this,
       # or nix-env complains: https://github.com/NixOS/nix/blob/2.18.8/src/nix-env/nix-env.cc#L963

pkgs/stdenv/generic/make-derivation.nix

@@ -747,9 +747,6 @@ let
       );
 
     let
-      mainProgram = meta.mainProgram or null;
-      env' = env // lib.optionalAttrs (mainProgram != null) { NIX_MAIN_PROGRAM = mainProgram; };
-
       derivationArg = makeDerivationArgument (
         removeAttrs attrs ([
           "meta"
@@ -776,11 +773,11 @@ let
 
       checkedEnv =
         let
-          overlappingNames = attrNames (builtins.intersectAttrs env' derivationArg);
+          overlappingNames = attrNames (builtins.intersectAttrs env derivationArg);
           prettyPrint = lib.generators.toPretty { };
           makeError =
             name:
-            "  - ${name}: in `env`: ${prettyPrint env'.${name}}; in derivation arguments: ${
+            "  - ${name}: in `env`: ${prettyPrint env.${name}}; in derivation arguments: ${
                 prettyPrint derivationArg.${name}
               }";
           errors = lib.concatMapStringsSep "\n" makeError overlappingNames;
@@ -794,7 +791,7 @@ let
           assert assertMsg (isString v || isBool v || isInt v || isDerivation v)
             "The `env` attribute set can only contain derivation, string, boolean or integer attributes. The `${n}` attribute is of type ${builtins.typeOf v}.";
           v
-        ) env';
+        ) env;
 
       # Fixed-output derivations may not reference other paths, which means that
       # for a fixed-output derivation, the corresponding inputDerivation should