tests.srcOnly: Add test cases for equivalences in the interface

pkgs/build-support/src-only/tests.nix

@@ -1,28 +1,78 @@
 {
   runCommand,
   srcOnly,
+  hello,
   emptyDirectory,
   glibc,
+  stdenv,
+  testers,
 }:
 
 let
   emptySrc = srcOnly emptyDirectory;
   glibcSrc = srcOnly glibc;
+
+  # It can be invoked in a number of ways. Let's make sure they're equivalent.
+  glibcSrcDrvAttrs = srcOnly glibc.drvAttrs;
+  # glibcSrcFreeform = # ???;
+  helloSrc = srcOnly hello;
+  helloSrcDrvAttrs = srcOnly hello.drvAttrs;
+
+  # The srcOnly <drv> invocation leaks a lot of attrs into the srcOnly derivation,
+  # so for comparing with the freeform invocation, we need to make a selection.
+  # Otherwise, we'll be comparing against whatever attribute the fancy hello drv
+  # has.
+  helloDrvSimple = stdenv.mkDerivation {
+    inherit (hello)
+      name
+      pname
+      version
+      src
+      patches
+      ;
+  };
+  helloDrvSimpleSrc = srcOnly helloDrvSimple;
+  helloDrvSimpleSrcFreeform = srcOnly {
+    inherit (helloDrvSimple)
+      name
+      pname
+      version
+      src
+      patches
+      stdenv
+      ;
+  };
+
 in
 
-runCommand "srcOnly-tests" { } ''
-  # Test that emptySrc is empty
-  if [ -n "$(ls -A ${emptySrc})" ]; then
-    echo "emptySrc is not empty"
-    exit 1
-  fi
+runCommand "srcOnly-tests"
+  {
+    moreTests = [
+      (testers.testEqualDerivation "glibcSrcDrvAttrs == glibcSrc" glibcSrcDrvAttrs glibcSrc)
+      # (testers.testEqualDerivation
+      #   "glibcSrcFreeform == glibcSrc"
+      #   glibcSrcFreeform
+      #   glibcSrc)
+      (testers.testEqualDerivation "helloSrcDrvAttrs == helloSrc" helloSrcDrvAttrs helloSrc)
+      (testers.testEqualDerivation "helloDrvSimpleSrcFreeform == helloDrvSimpleSrc"
+        helloDrvSimpleSrcFreeform
+        helloDrvSimpleSrc
+      )
+    ];
+  }
+  ''
+    # Test that emptySrc is empty
+    if [ -n "$(ls -A ${emptySrc})" ]; then
+      echo "emptySrc is not empty"
+      exit 1
+    fi
 
-  # Test that glibcSrc is not empty
-  if [ -z "$(ls -A ${glibcSrc})" ]; then
-    echo "glibcSrc is empty"
-    exit 1
-  fi
+    # Test that glibcSrc is not empty
+    if [ -z "$(ls -A ${glibcSrc})" ]; then
+      echo "glibcSrc is empty"
+      exit 1
+    fi
 
-  # Make $out exist to avoid build failure
-  mkdir -p $out
-''
+    # Make $out exist to avoid build failure
+    mkdir -p $out
+  ''