writeCBin: Add meta.mainProgram

... and add tests.

pkgs/build-support/trivial-builders/default.nix

@@ -242,7 +242,11 @@ rec {
 
 
   */
-  writeScriptBin = name: text: writeTextFile {inherit name text; executable = true; destination = "/bin/${name}";};
+  writeScriptBin = name: text: writeTextFile {
+    inherit name text;
+    executable = true;
+    destination = "/bin/${name}";
+  };
 
   /*
     Similar to writeScript. Writes a Shell script and checks its syntax.
@@ -374,6 +378,9 @@ rec {
       # Pointless to do this on a remote machine.
       preferLocalBuild = true;
       allowSubstitutes = false;
+      meta = {
+        mainProgram = name;
+      };
     }
     ''
       n=$out/bin/$name

pkgs/build-support/trivial-builders/test/writeCBin.nix

@@ -0,0 +1,43 @@
+/*
+  Run with:
+
+      cd nixpkgs
+      nix-build -A tests.trivial-builders.writeCBin
+*/
+
+{ lib, writeCBin, runCommand }:
+let
+  output = "hello";
+  pkg = writeCBin "test-script" ''
+    #include <stdio.h>
+    int main () {
+      printf("hello\n");
+      return 0;
+    }
+  '';
+in
+  assert pkg.meta.mainProgram == "test-script";
+  runCommand "test-writeCBin" { } ''
+
+    echo Testing with getExe...
+
+    target=${lib.getExe pkg}
+    expected=${lib.escapeShellArg output}
+    got=$("$target")
+    if [[ "$got" != "$expected" ]]; then
+      echo "wrong output: expected $expected, got $got"
+      exit 1
+    fi
+
+    echo Testing with makeBinPath...
+
+    PATH="${lib.makeBinPath [ pkg ]}:$PATH"
+    got=$(test-script)
+    if [[ "$got" != "$expected" ]]; then
+      echo "wrong output: expected $expected, got $got"
+      exit 1
+    fi
+
+    touch $out
+  ''
+

pkgs/build-support/trivial-builders/test/writeScriptBin.nix

@@ -0,0 +1,39 @@
+/*
+  Run with:
+
+      cd nixpkgs
+      nix-build -A tests.trivial-builders.writeShellScriptBin
+*/
+
+{ lib, writeScriptBin, runCommand }:
+let
+  output = "hello";
+  pkg = writeScriptBin "test-script" ''
+    echo ${lib.escapeShellArg output}
+  '';
+in
+  assert pkg.meta.mainProgram == "test-script";
+  runCommand "test-writeScriptBin" { } ''
+
+    echo Testing with getExe...
+
+    target=${lib.getExe pkg}
+    expected=${lib.escapeShellArg output}
+    got=$("$target")
+    if [[ "$got" != "$expected" ]]; then
+      echo "wrong output: expected $expected, got $got"
+      exit 1
+    fi
+
+    echo Testing with makeBinPath...
+
+    PATH="${lib.makeBinPath [ pkg ]}:$PATH"
+    got=$(test-script)
+    if [[ "$got" != "$expected" ]]; then
+      echo "wrong output: expected $expected, got $got"
+      exit 1
+    fi
+
+    touch $out
+  ''
+

pkgs/build-support/trivial-builders/test/writeShellScriptBin.nix

@@ -0,0 +1,39 @@
+/*
+  Run with:
+
+      cd nixpkgs
+      nix-build -A tests.trivial-builders.writeShellScriptBin
+*/
+
+{ lib, writeShellScriptBin, runCommand }:
+let
+  output = "hello";
+  pkg = writeShellScriptBin "test-script" ''
+    echo ${lib.escapeShellArg output}
+  '';
+in
+  assert pkg.meta.mainProgram == "test-script";
+  runCommand "test-writeShellScriptBin" { } ''
+
+    echo Testing with getExe...
+
+    target=${lib.getExe pkg}
+    expected=${lib.escapeShellArg output}
+    got=$("$target")
+    if [[ "$got" != "$expected" ]]; then
+      echo "wrong output: expected $expected, got $got"
+      exit 1
+    fi
+
+    echo Testing with makeBinPath...
+
+    PATH="${lib.makeBinPath [ pkg ]}:$PATH"
+    got=$(test-script)
+    if [[ "$got" != "$expected" ]]; then
+      echo "wrong output: expected $expected, got $got"
+      exit 1
+    fi
+
+    touch $out
+  ''
+

pkgs/test/default.nix

@@ -67,9 +67,12 @@ with pkgs;
   cuda = callPackage ./cuda { };
 
   trivial-builders = recurseIntoAttrs {
+    writeCBin = callPackage ../build-support/trivial-builders/test/writeCBin.nix {};
+    writeScriptBin = callPackage ../build-support/trivial-builders/test/writeScriptBin.nix {};
     writeStringReferencesToFile = callPackage ../build-support/trivial-builders/test/writeStringReferencesToFile.nix {};
     writeTextFile = callPackage ../build-support/trivial-builders/test/write-text-file.nix {};
     writeShellScript = callPackage ../build-support/trivial-builders/test/write-shell-script.nix {};
+    writeShellScriptBin = callPackage ../build-support/trivial-builders/test/writeShellScriptBin.nix {};
     references = callPackage ../build-support/trivial-builders/test/references.nix {};
     overriding = callPackage ../build-support/trivial-builders/test-overriding.nix {};
     concat = callPackage ../build-support/trivial-builders/test/concat-test.nix {};