Merge commit 'a21c2fa3ea2b88e698db6fc151d9c7259ae14d96'

17 files changed, 351 insertions, 57 deletions

diff --git a/nixpkgs/lib/attrsets.nix b/nixpkgs/lib/attrsets.nix
index 086c3d746fc..32994432d53 100644
--- a/nixpkgs/lib/attrsets.nix
+++ b/nixpkgs/lib/attrsets.nix
@@ -60,7 +60,7 @@ rec {
       [ { name = head attrPath; value = setAttrByPath (tail attrPath) value; } ];
 
 
-  /* Like `getAttrPath' without a default value. If it doesn't find the
+  /* Like `attrByPath' without a default value. If it doesn't find the
      path it will throw.
 
      Example:
diff --git a/nixpkgs/lib/cli.nix b/nixpkgs/lib/cli.nix
new file mode 100644
index 00000000000..c96d4dbb043
--- /dev/null
+++ b/nixpkgs/lib/cli.nix
@@ -0,0 +1,83 @@
+{ lib }:
+
+rec {
+  /* Automatically convert an attribute set to command-line options.
+
+     This helps protect against malformed command lines and also to reduce
+     boilerplate related to command-line construction for simple use cases.
+
+     `toGNUCommandLine` returns a list of nix strings.
+     `toGNUCommandLineShell` returns an escaped shell string.
+
+     Example:
+       cli.toGNUCommandLine {} {
+         data = builtins.toJSON { id = 0; };
+         X = "PUT";
+         retry = 3;
+         retry-delay = null;
+         url = [ "https://example.com/foo" "https://example.com/bar" ];
+         silent = false;
+         verbose = true;
+       }
+       => [
+         "-X" "PUT"
+         "--data" "{\"id\":0}"
+         "--retry" "3"
+         "--url" "https://example.com/foo"
+         "--url" "https://example.com/bar"
+         "--verbose"
+       ]
+
+       cli.toGNUCommandLineShell {} {
+         data = builtins.toJSON { id = 0; };
+         X = "PUT";
+         retry = 3;
+         retry-delay = null;
+         url = [ "https://example.com/foo" "https://example.com/bar" ];
+         silent = false;
+         verbose = true;
+       }
+       => "'-X' 'PUT' '--data' '{\"id\":0}' '--retry' '3' '--url' 'https://example.com/foo' '--url' 'https://example.com/bar' '--verbose'";
+  */
+  toGNUCommandLineShell =
+    options: attrs: lib.escapeShellArgs (toGNUCommandLine options attrs);
+
+  toGNUCommandLine = {
+    # how to string-format the option name;
+    # by default one character is a short option (`-`),
+    # more than one characters a long option (`--`).
+    mkOptionName ?
+      k: if builtins.stringLength k == 1
+          then "-${k}"
+          else "--${k}",
+
+    # how to format a boolean value to a command list;
+    # by default it’s a flag option
+    # (only the option name if true, left out completely if false).
+    mkBool ? k: v: lib.optional v (mkOptionName k),
+
+    # how to format a list value to a command list;
+    # by default the option name is repeated for each value
+    # and `mkOption` is applied to the values themselves.
+    mkList ? k: v: lib.concatMap (mkOption k) v,
+
+    # how to format any remaining value to a command list;
+    # on the toplevel, booleans and lists are handled by `mkBool` and `mkList`,
+    # though they can still appear as values of a list.
+    # By default, everything is printed verbatim and complex types
+    # are forbidden (lists, attrsets, functions). `null` values are omitted.
+    mkOption ?
+      k: v: if v == null
+            then []
+            else [ (mkOptionName k) (lib.generators.mkValueStringDefault {} v) ]
+    }:
+    options:
+      let
+        render = k: v:
+          if      builtins.isBool v then mkBool k v
+          else if builtins.isList v then mkList k v
+          else mkOption k v;
+
+      in
+        builtins.concatLists (lib.mapAttrsToList render options);
+}
diff --git a/nixpkgs/lib/default.nix b/nixpkgs/lib/default.nix
index 9f7a088d792..d2fe018aa6a 100644
--- a/nixpkgs/lib/default.nix
+++ b/nixpkgs/lib/default.nix
@@ -37,10 +37,13 @@ let
     licenses = callLibs ./licenses.nix;
     systems = callLibs ./systems;
 
+    # serialization
+    cli = callLibs ./cli.nix;
+    generators = callLibs ./generators.nix;
+
     # misc
     asserts = callLibs ./asserts.nix;
     debug = callLibs ./debug.nix;
-    generators = callLibs ./generators.nix;
     misc = callLibs ./deprecated.nix;
 
     # domain-specific
@@ -100,7 +103,7 @@ let
     inherit (sources) pathType pathIsDirectory cleanSourceFilter
       cleanSource sourceByRegex sourceFilesBySuffices
       commitIdFromGitRepo cleanSourceWith pathHasContext
-      canCleanSource;
+      canCleanSource pathIsRegularFile pathIsGitRepo;
     inherit (modules) evalModules unifyModuleSyntax
       applyIfFunction mergeModules
       mergeModules' mergeOptionDecls evalOptionValue mergeDefinitions
diff --git a/nixpkgs/lib/generators.nix b/nixpkgs/lib/generators.nix
index a71654bec6c..a64e94bd5cb 100644
--- a/nixpkgs/lib/generators.nix
+++ b/nixpkgs/lib/generators.nix
@@ -46,7 +46,10 @@ rec {
     else if isList     v then err "lists" v
     # same as for lists, might want to replace
     else if isAttrs    v then err "attrsets" v
+    # functions can’t be printed of course
     else if isFunction v then err "functions" v
+    # let’s not talk about floats. There is no sensible `toString` for them.
+    else if isFloat    v then err "floats" v
     else err "this value is" (toString v);
 
 
diff --git a/nixpkgs/lib/licenses.nix b/nixpkgs/lib/licenses.nix
index 986b7fa1fdd..e2f94e565ce 100644
--- a/nixpkgs/lib/licenses.nix
+++ b/nixpkgs/lib/licenses.nix
@@ -536,11 +536,6 @@ lib.mapAttrs (n: v: v // { shortName = n; }) {
     fullName  = "University of Illinois/NCSA Open Source License";
   };
 
-  notion_lgpl = {
-    url = "https://raw.githubusercontent.com/raboof/notion/master/LICENSE";
-    fullName = "Notion modified LGPL";
-  };
-
   nposl3 = spdx {
     spdxId = "NPOSL-3.0";
     fullName = "Non-Profit Open Software License 3.0";
diff --git a/nixpkgs/lib/modules.nix b/nixpkgs/lib/modules.nix
index 38d6ac8cd91..2b1faf4f0c2 100644
--- a/nixpkgs/lib/modules.nix
+++ b/nixpkgs/lib/modules.nix
@@ -41,7 +41,13 @@ rec {
 
         options = {
           _module.args = mkOption {
-            type = types.attrsOf types.unspecified;
+            # Because things like `mkIf` are entirely useless for
+            # `_module.args` (because there's no way modules can check which
+            # arguments were passed), we'll use `lazyAttrsOf` which drops
+            # support for that, in turn it's lazy in its values. This means e.g.
+            # a `_module.args.pkgs = import (fetchTarball { ... }) {}` won't
+            # start a download when `pkgs` wasn't evaluated.
+            type = types.lazyAttrsOf types.unspecified;
             internal = true;
             description = "Arguments passed to each module.";
           };
@@ -151,8 +157,8 @@ rec {
       filterModules = modulesPath: { disabled, modules }:
         let
           moduleKey = m: if isString m then toString modulesPath + "/" + m else toString m;
-          disabledKeys = listToAttrs (map (k: nameValuePair (moduleKey k) null) disabled);
-          keyFilter = filter (attrs: ! disabledKeys ? ${attrs.key});
+          disabledKeys = map moduleKey disabled;
+          keyFilter = filter (attrs: ! elem attrs.key disabledKeys);
         in map (attrs: attrs.module) (builtins.genericClosure {
           startSet = keyFilter modules;
           operator = attrs: keyFilter attrs.modules;
@@ -365,16 +371,9 @@ rec {
         else
           mergeDefinitions loc opt.type defs';
 
-
-      # The value with a check that it is defined
-      valueDefined = if res.isDefined then res.mergedValue else
-        # (nixos-option detects this specific error message and gives it special
-        # handling.  If changed here, please change it there too.)
-        throw "The option `${showOption loc}' is used but not defined.";
-
       # Apply the 'apply' function to the merged value. This allows options to
       # yield a value computed from the definitions
-      value = if opt ? apply then opt.apply valueDefined else valueDefined;
+      value = if opt ? apply then opt.apply res.mergedValue else res.mergedValue;
 
     in opt //
       { value = builtins.addErrorContext "while evaluating the option `${showOption loc}':" value;
@@ -408,11 +407,17 @@ rec {
       };
     defsFinal = defsFinal'.values;
 
-    # Type-check the remaining definitions, and merge them.
-    mergedValue = foldl' (res: def:
-      if type.check def.value then res
-      else throw "The option value `${showOption loc}' in `${def.file}' is not of type `${type.description}'.")
-      (type.merge loc defsFinal) defsFinal;
+    # Type-check the remaining definitions, and merge them. Or throw if no definitions.
+    mergedValue =
+      if isDefined then
+        foldl' (res: def:
+          if type.check def.value then res
+          else throw "The option value `${showOption loc}' in `${def.file}' is not of type `${type.description}'."
+        ) (type.merge loc defsFinal) defsFinal
+      else
+        # (nixos-option detects this specific error message and gives it special
+        # handling.  If changed here, please change it there too.)
+        throw "The option `${showOption loc}' is used but not defined.";
 
     isDefined = defsFinal != [];
 
@@ -759,12 +764,15 @@ rec {
       fromOpt = getAttrFromPath from options;
       toOf = attrByPath to
         (abort "Renaming error: option `${showOption to}' does not exist.");
+      toType = let opt = attrByPath to {} options; in opt.type or null;
     in
     {
       options = setAttrByPath from (mkOption {
         inherit visible;
         description = "Alias of <option>${showOption to}</option>.";
         apply = x: use (toOf config);
+      } // optionalAttrs (toType != null) {
+        type = toType;
       });
       config = mkMerge [
         {
diff --git a/nixpkgs/lib/sources.nix b/nixpkgs/lib/sources.nix
index 51bcf5559e3..05519c3e392 100644
--- a/nixpkgs/lib/sources.nix
+++ b/nixpkgs/lib/sources.nix
@@ -9,6 +9,9 @@ rec {
   # Returns true if the path exists and is a directory, false otherwise
   pathIsDirectory = p: if builtins.pathExists p then (pathType p) == "directory" else false;
 
+  # Returns true if the path exists and is a regular file, false otherwise
+  pathIsRegularFile = p: if builtins.pathExists p then (pathType p) == "regular" else false;
+
   # Bring in a path as a source, filtering out all Subversion and CVS
   # directories, as well as backup files (*~).
   cleanSourceFilter = name: type: let baseName = baseNameOf (toString name); in ! (
@@ -102,6 +105,7 @@ rec {
       in type == "directory" || lib.any (ext: lib.hasSuffix ext base) exts;
     in cleanSourceWith { inherit filter; src = path; };
 
+  pathIsGitRepo = path: (builtins.tryEval (commitIdFromGitRepo path)).success;
 
   # Get the commit id of a git repo
   # Example: commitIdFromGitRepo <nixpkgs/.git>
@@ -110,24 +114,45 @@ rec {
       with builtins;
         let fileName       = toString path + "/" + file;
             packedRefsName = toString path + "/packed-refs";
-        in if lib.pathExists fileName
+            absolutePath   = base: path:
+              if lib.hasPrefix "/" path
+              then path
+              else toString (/. + "${base}/${path}");
+        in if pathIsRegularFile path
+           # Resolve git worktrees. See gitrepository-layout(5)
+           then
+             let m   = match "^gitdir: (.*)$" (lib.fileContents path);
+             in if m == null
+                then throw ("File contains no gitdir reference: " + path)
+                else
+                  let gitDir     = absolutePath (dirOf path) (lib.head m);
+                      commonDir' = if pathIsRegularFile "${gitDir}/commondir"
+                                   then lib.fileContents "${gitDir}/commondir"
+                                   else gitDir;
+                      commonDir  = absolutePath gitDir commonDir';
+                      refFile    = lib.removePrefix "${commonDir}/" "${gitDir}/${file}";
+                  in readCommitFromFile refFile commonDir
+
+           else if pathIsRegularFile fileName
+           # Sometimes git stores the commitId directly in the file but
+           # sometimes it stores something like: «ref: refs/heads/branch-name»
            then
              let fileContent = lib.fileContents fileName;
-                 # Sometimes git stores the commitId directly in the file but
-                 # sometimes it stores something like: «ref: refs/heads/branch-name»
                  matchRef    = match "^ref: (.*)$" fileContent;
-             in if   matchRef == null
+             in if  matchRef == null
                 then fileContent
                 else readCommitFromFile (lib.head matchRef) path
+
+           else if pathIsRegularFile packedRefsName
            # Sometimes, the file isn't there at all and has been packed away in the
            # packed-refs file, so we have to grep through it:
-           else if lib.pathExists packedRefsName
            then
              let fileContent = readFile packedRefsName;
                  matchRef    = match (".*\n([^\n ]*) " + file + "\n.*") fileContent;
-             in if   matchRef == null
+             in if  matchRef == null
                 then throw ("Could not find " + file + " in " + packedRefsName)
                 else lib.head matchRef
+
            else throw ("Not a .git directory: " + path);
     in readCommitFromFile "HEAD";
 
diff --git a/nixpkgs/lib/systems/examples.nix b/nixpkgs/lib/systems/examples.nix
index cb8bc3de6c4..19b3790ecbe 100644
--- a/nixpkgs/lib/systems/examples.nix
+++ b/nixpkgs/lib/systems/examples.nix
@@ -170,8 +170,8 @@ rec {
   iphone64 = {
     config = "aarch64-apple-ios";
     # config = "aarch64-apple-darwin14";
-    sdkVer = "10.2";
-    xcodeVer = "8.2";
+    sdkVer = "12.4";
+    xcodeVer = "10.3";
     xcodePlatform = "iPhoneOS";
     useiOSPrebuilt = true;
     platform = {};
@@ -180,8 +180,8 @@ rec {
   iphone32 = {
     config = "armv7a-apple-ios";
     # config = "arm-apple-darwin10";
-    sdkVer = "10.2";
-    xcodeVer = "8.2";
+    sdkVer = "12.4";
+    xcodeVer = "10.3";
     xcodePlatform = "iPhoneOS";
     useiOSPrebuilt = true;
     platform = {};
@@ -190,8 +190,8 @@ rec {
   iphone64-simulator = {
     config = "x86_64-apple-ios";
     # config = "x86_64-apple-darwin14";
-    sdkVer = "10.2";
-    xcodeVer = "8.2";
+    sdkVer = "12.4";
+    xcodeVer = "10.3";
     xcodePlatform = "iPhoneSimulator";
     useiOSPrebuilt = true;
     platform = {};
@@ -200,8 +200,8 @@ rec {
   iphone32-simulator = {
     config = "i686-apple-ios";
     # config = "i386-apple-darwin11";
-    sdkVer = "10.2";
-    xcodeVer = "8.2";
+    sdkVer = "12.4";
+    xcodeVer = "10.3";
     xcodePlatform = "iPhoneSimulator";
     useiOSPrebuilt = true;
     platform = {};
diff --git a/nixpkgs/lib/tests/misc.nix b/nixpkgs/lib/tests/misc.nix
index b064faa1e1b..59ed1e507e2 100644
--- a/nixpkgs/lib/tests/misc.nix
+++ b/nixpkgs/lib/tests/misc.nix
@@ -441,4 +441,41 @@ runTests {
     expected  = "«foo»";
   };
 
+
+# CLI
+
+  testToGNUCommandLine = {
+    expr = cli.toGNUCommandLine {} {
+      data = builtins.toJSON { id = 0; };
+      X = "PUT";
+      retry = 3;
+      retry-delay = null;
+      url = [ "https://example.com/foo" "https://example.com/bar" ];
+      silent = false;
+      verbose = true;
+    };
+
+    expected = [
+      "-X" "PUT"
+      "--data" "{\"id\":0}"
+      "--retry" "3"
+      "--url" "https://example.com/foo"
+      "--url" "https://example.com/bar"
+      "--verbose"
+    ];
+  };
+
+  testToGNUCommandLineShell = {
+    expr = cli.toGNUCommandLineShell {} {
+      data = builtins.toJSON { id = 0; };
+      X = "PUT";
+      retry = 3;
+      retry-delay = null;
+      url = [ "https://example.com/foo" "https://example.com/bar" ];
+      silent = false;
+      verbose = true;
+    };
+
+    expected = "'-X' 'PUT' '--data' '{\"id\":0}' '--retry' '3' '--url' 'https://example.com/foo' '--url' 'https://example.com/bar' '--verbose'";
+  };
 }
diff --git a/nixpkgs/lib/tests/modules.sh b/nixpkgs/lib/tests/modules.sh
index 2997fb1ada1..8cd632a439c 100755
--- a/nixpkgs/lib/tests/modules.sh
+++ b/nixpkgs/lib/tests/modules.sh
@@ -12,7 +12,7 @@ evalConfig() {
     local attr=$1
     shift;
     local script="import ./default.nix { modules = [ $@ ];}"
-    nix-instantiate --timeout 1 -E "$script" -A "$attr" --eval-only --show-trace
+    nix-instantiate --timeout 1 -E "$script" -A "$attr" --eval-only --show-trace --read-write-mode
 }
 
 reportFailure() {
@@ -174,8 +174,7 @@ checkConfigOutput "true" config.submodule.inner ./declare-submoduleWith-modules.
 checkConfigOutput "true" config.submodule.outer ./declare-submoduleWith-modules.nix
 
 ## Paths should be allowed as values and work as expected
-# Temporarily disabled until https://github.com/NixOS/nixpkgs/pull/76861
-#checkConfigOutput "true" config.submodule.enable ./declare-submoduleWith-path.nix
+checkConfigOutput "true" config.submodule.enable ./declare-submoduleWith-path.nix
 
 # Check that disabledModules works recursively and correctly
 checkConfigOutput "true" config.enable ./disable-recursive/main.nix
@@ -183,6 +182,18 @@ checkConfigOutput "true" config.enable ./disable-recursive/{main.nix,disable-foo
 checkConfigOutput "true" config.enable ./disable-recursive/{main.nix,disable-bar.nix}
 checkConfigError 'The option .* defined in .* does not exist' config.enable ./disable-recursive/{main.nix,disable-foo.nix,disable-bar.nix}
 
+# Check that imports can depend on derivations
+checkConfigOutput "true" config.enable ./import-from-store.nix
+
+# Check attrsOf and lazyAttrsOf. Only lazyAttrsOf should be lazy, and only
+# attrsOf should work with conditional definitions
+# In addition, lazyAttrsOf should honor an options emptyValue
+checkConfigError "is not lazy" config.isLazy ./declare-attrsOf.nix ./attrsOf-lazy-check.nix
+checkConfigOutput "true" config.isLazy ./declare-lazyAttrsOf.nix ./attrsOf-lazy-check.nix
+checkConfigOutput "true" config.conditionalWorks ./declare-attrsOf.nix ./attrsOf-conditional-check.nix
+checkConfigOutput "false" config.conditionalWorks ./declare-lazyAttrsOf.nix ./attrsOf-conditional-check.nix
+checkConfigOutput "empty" config.value.foo ./declare-lazyAttrsOf.nix ./attrsOf-conditional-check.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass
diff --git a/nixpkgs/lib/tests/modules/attrsOf-conditional-check.nix b/nixpkgs/lib/tests/modules/attrsOf-conditional-check.nix
new file mode 100644
index 00000000000..0f00ebca155
--- /dev/null
+++ b/nixpkgs/lib/tests/modules/attrsOf-conditional-check.nix
@@ -0,0 +1,7 @@
+{ lib, config, ... }: {
+  options.conditionalWorks = lib.mkOption {
+    default = ! config.value ? foo;
+  };
+
+  config.value.foo = lib.mkIf false "should not be defined";
+}
diff --git a/nixpkgs/lib/tests/modules/attrsOf-lazy-check.nix b/nixpkgs/lib/tests/modules/attrsOf-lazy-check.nix
new file mode 100644
index 00000000000..ec5b418b15a
--- /dev/null
+++ b/nixpkgs/lib/tests/modules/attrsOf-lazy-check.nix
@@ -0,0 +1,7 @@
+{ lib, config, ... }: {
+  options.isLazy = lib.mkOption {
+    default = ! config.value ? foo;
+  };
+
+  config.value.bar = throw "is not lazy";
+}
diff --git a/nixpkgs/lib/tests/modules/declare-attrsOf.nix b/nixpkgs/lib/tests/modules/declare-attrsOf.nix
new file mode 100644
index 00000000000..b3999de7e5f
--- /dev/null
+++ b/nixpkgs/lib/tests/modules/declare-attrsOf.nix
@@ -0,0 +1,6 @@
+{ lib, ... }: {
+  options.value = lib.mkOption {
+    type = lib.types.attrsOf lib.types.str;
+    default = {};
+  };
+}
diff --git a/nixpkgs/lib/tests/modules/declare-lazyAttrsOf.nix b/nixpkgs/lib/tests/modules/declare-lazyAttrsOf.nix
new file mode 100644
index 00000000000..1d9fec25f90
--- /dev/null
+++ b/nixpkgs/lib/tests/modules/declare-lazyAttrsOf.nix
@@ -0,0 +1,6 @@
+{ lib, ... }: {
+  options.value = lib.mkOption {
+    type = lib.types.lazyAttrsOf (lib.types.str // { emptyValue.value = "empty"; });
+    default = {};
+  };
+}
diff --git a/nixpkgs/lib/tests/modules/import-from-store.nix b/nixpkgs/lib/tests/modules/import-from-store.nix
new file mode 100644
index 00000000000..f5af22432ce
--- /dev/null
+++ b/nixpkgs/lib/tests/modules/import-from-store.nix
@@ -0,0 +1,11 @@
+{ lib, ... }:
+{
+
+  imports = [
+    "${builtins.toFile "drv" "{}"}"
+    ./declare-enable.nix
+    ./define-enable.nix
+  ];
+
+}
+
diff --git a/nixpkgs/lib/trivial.nix b/nixpkgs/lib/trivial.nix
index 3a25e31fb05..a281cd70fb0 100644
--- a/nixpkgs/lib/trivial.nix
+++ b/nixpkgs/lib/trivial.nix
@@ -191,7 +191,7 @@ rec {
     let
       revisionFile = "${toString ./..}/.git-revision";
       gitRepo      = "${toString ./..}/.git";
-    in if lib.pathIsDirectory gitRepo
+    in if lib.pathIsGitRepo gitRepo
        then lib.commitIdFromGitRepo gitRepo
        else if lib.pathExists revisionFile then lib.fileContents revisionFile
        else default;
diff --git a/nixpkgs/lib/types.nix b/nixpkgs/lib/types.nix
index 4872a676657..6fd6de7e1fd 100644
--- a/nixpkgs/lib/types.nix
+++ b/nixpkgs/lib/types.nix
@@ -65,6 +65,11 @@ rec {
       # definition values and locations (e.g. [ { file = "/foo.nix";
       # value = 1; } { file = "/bar.nix"; value = 2 } ]).
       merge ? mergeDefaultOption
+    , # Whether this type has a value representing nothingness. If it does,
+      # this should be a value of the form { value = <the nothing value>; }
+      # If it doesn't, this should be {}
+      # This may be used when a value is required for `mkIf false`. This allows the extra laziness in e.g. `lazyAttrsOf`.
+      emptyValue ? {}
     , # Return a flat list of sub-options.  Used to generate
       # documentation.
       getSubOptions ? prefix: {}
@@ -88,7 +93,7 @@ rec {
       functor ? defaultFunctor name
     }:
     { _type = "option-type";
-      inherit name check merge getSubOptions getSubModules substSubModules typeMerge functor;
+      inherit name check merge emptyValue getSubOptions getSubModules substSubModules typeMerge functor;
       description = if description == null then name else description;
     };
 
@@ -225,6 +230,7 @@ rec {
       description = "attribute set";
       check = isAttrs;
       merge = loc: foldl' (res: def: mergeAttrs res def.value) {};
+      emptyValue = { value = {}; };
     };
 
     # derivation is a reserved keyword.
@@ -265,6 +271,7 @@ rec {
             ) def.value
           else
             throw "The option value `${showOption loc}` in `${def.file}` is not a list.") defs)));
+      emptyValue = { value = {}; };
       getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["*"]);
       getSubModules = elemType.getSubModules;
       substSubModules = m: listOf (elemType.substSubModules m);
@@ -273,7 +280,10 @@ rec {
 
     nonEmptyListOf = elemType:
       let list = addCheck (types.listOf elemType) (l: l != []);
-      in list // { description = "non-empty " + list.description; };
+      in list // {
+        description = "non-empty " + list.description;
+        # Note: emptyValue is left as is, because another module may define an element.
+      };
 
     attrsOf = elemType: mkOptionType rec {
       name = "attrsOf";
@@ -285,12 +295,37 @@ rec {
           )
           # Push down position info.
           (map (def: mapAttrs (n: v: { inherit (def) file; value = v; }) def.value) defs)));
+      emptyValue = { value = {}; };
       getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<name>"]);
       getSubModules = elemType.getSubModules;
       substSubModules = m: attrsOf (elemType.substSubModules m);
       functor = (defaultFunctor name) // { wrapped = elemType; };
     };
 
+    # A version of attrsOf that's lazy in its values at the expense of
+    # conditional definitions not working properly. E.g. defining a value with
+    # `foo.attr = mkIf false 10`, then `foo ? attr == true`, whereas with
+    # attrsOf it would correctly be `false`. Accessing `foo.attr` would throw an
+    # error that it's not defined. Use only if conditional definitions don't make sense.
+    lazyAttrsOf = elemType: mkOptionType rec {
+      name = "lazyAttrsOf";
+      description = "lazy attribute set of ${elemType.description}s";
+      check = isAttrs;
+      merge = loc: defs:
+        zipAttrsWith (name: defs:
+          let merged = mergeDefinitions (loc ++ [name]) elemType defs;
+          # mergedValue will trigger an appropriate error when accessed
+          in merged.optionalValue.value or elemType.emptyValue.value or merged.mergedValue
+        )
+        # Push down position info.
+        (map (def: mapAttrs (n: v: { inherit (def) file; value = v; }) def.value) defs);
+      emptyValue = { value = {}; };
+      getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<name>"]);
+      getSubModules = elemType.getSubModules;
+      substSubModules = m: lazyAttrsOf (elemType.substSubModules m);
+      functor = (defaultFunctor name) // { wrapped = elemType; };
+    };
+
     # List or attribute set of ...
     loaOf = elemType:
       let
@@ -305,29 +340,79 @@ rec {
             let
               padWidth = stringLength (toString (length def.value));
               unnamed = i: unnamedPrefix + fixedWidthNumber padWidth i;
+              anyString = placeholder "name";
+              nameAttrs = [
+                { path = [ "environment" "etc" ];
+                  name = "target";
+                }
+                { path = [ "containers" anyString "bindMounts" ];
+                  name = "mountPoint";
+                }
+                { path = [ "programs" "ssh" "knownHosts" ];
+                  # hostNames is actually a list so we would need to handle it only when singleton
+                  name = "hostNames";
+                }
+                { path = [ "fileSystems" ];
+                  name = "mountPoint";
+                }
+                { path = [ "boot" "specialFileSystems" ];
+                  name = "mountPoint";
+                }
+                { path = [ "services" "znapzend" "zetup" ];
+                  name = "dataset";
+                }
+                { path = [ "services" "znapzend" "zetup" anyString "destinations" ];
+                  name = "label";
+                }
+                { path = [ "services" "geoclue2" "appConfig" ];
+                  name = "desktopID";
+                }
+              ];
+              matched = let
+                equals = a: b: b == anyString || a == b;
+                fallback = { name = "name"; };
+              in findFirst ({ path, ... }: all (v: v == true) (zipListsWith equals loc path)) fallback nameAttrs;
+              nameAttr = matched.name;
+              nameValueOld = value:
+                if isList value then
+                  if length value > 0 then
+                    "[ " + concatMapStringsSep " " escapeNixString value + " ]"
+                  else
+                    "[ ]"
+                else
+                  escapeNixString value;
+              nameValueNew = value: unnamed:
+                if isList value then
+                  if length value > 0 then
+                    head value
+                  else
+                    unnamed
+                else
+                  value;
               res =
                 { inherit (def) file;
                   value = listToAttrs (
                     imap1 (elemIdx: elem:
-                      { name  = elem.name or (unnamed elemIdx);
+                      { name  = nameValueNew (elem.${nameAttr} or (unnamed elemIdx)) (unnamed elemIdx);
                         value = elem;
                       }) def.value);
                 };
               option = concatStringsSep "." loc;
               sample = take 3 def.value;
-              list = concatMapStrings (x: ''{ name = "${x.name or "unnamed"}"; ...} '') sample;
-              set = concatMapStrings (x: ''${x.name or "unnamed"} = {...}; '') sample;
+              more = lib.optionalString (length def.value > 3) "... ";
+              list = concatMapStrings (x: ''{ ${nameAttr} = ${nameValueOld (x.${nameAttr} or "unnamed")}; ...} '') sample;
+              set = concatMapStrings (x: ''${nameValueNew (x.${nameAttr} or "unnamed") "unnamed"} = {...}; '') sample;
               msg = ''
                 In file ${def.file}
                 a list is being assigned to the option config.${option}.
                 This will soon be an error as type loaOf is deprecated.
-                See https://git.io/fj2zm for more information.
+                See https://github.com/NixOS/nixpkgs/pull/63103 for more information.
                 Do
                   ${option} =
-                    { ${set}...}
+                    { ${set}${more}}
                 instead of
                   ${option} =
-                    [ ${list}...]
+                    [ ${list}${more}]
               '';
             in
               lib.warn msg res
@@ -339,6 +424,7 @@ rec {
         description = "list or attribute set of ${elemType.description}s";
         check = x: isList x || isAttrs x;
         merge = loc: defs: attrOnly.merge loc (convertAllLists loc defs);
+        emptyValue = { value = {}; };
         getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<name?>"]);
         getSubModules = elemType.getSubModules;
         substSubModules = m: loaOf (elemType.substSubModules m);
@@ -350,6 +436,7 @@ rec {
       name = "uniq";
       inherit (elemType) description check;
       merge = mergeOneOption;
+      emptyValue = elemType.emptyValue;
       getSubOptions = elemType.getSubOptions;
       getSubModules = elemType.getSubModules;
       substSubModules = m: uniq (elemType.substSubModules m);
@@ -367,6 +454,7 @@ rec {
         else if nrNulls != 0 then
           throw "The option `${showOption loc}` is defined both null and not null, in ${showFiles (getFiles defs)}."
         else elemType.merge loc defs;
+      emptyValue = { value = null; };
       getSubOptions = elemType.getSubOptions;
       getSubModules = elemType.getSubModules;
       substSubModules = m: nullOr (elemType.substSubModules m);
@@ -392,14 +480,16 @@ rec {
           else unify (if shorthandOnlyDefinesConfig then { config = value; } else value);
 
         allModules = defs: modules ++ imap1 (n: { value, file }:
-          # Annotate the value with the location of its definition for better error messages
-          coerce (lib.modules.unifyModuleSyntax file "${toString file}-${toString n}") value
+          if isAttrs value || isFunction value then
+            # Annotate the value with the location of its definition for better error messages
+            coerce (lib.modules.unifyModuleSyntax file "${toString file}-${toString n}") value
+          else value
         ) defs;
 
       in
       mkOptionType rec {
         name = "submodule";
-        check = x: isAttrs x || isFunction x;
+        check = x: isAttrs x || isFunction x || path.check x;
         merge = loc: defs:
           (evalModules {
             modules = allModules defs;
@@ -407,6 +497,7 @@ rec {
             args.name = last loc;
             prefix = loc;
           }).config;
+        emptyValue = { value = {}; };
         getSubOptions = prefix: (evalModules
           { inherit modules prefix specialArgs;
             # This is a work-around due to the fact that some sub-modules,
@@ -499,7 +590,7 @@ rec {
         tail' = tail ts;
       in foldl' either head' tail';
 
-    # Either value of type `finalType` or `coercedType`, the latter is
+    # Either value of type `coercedType` or `finalType`, the former is
     # converted to `finalType` using `coerceFunc`.
     coercedTo = coercedType: coerceFunc: finalType:
       assert lib.assertMsg (coercedType.getSubModules == null)
@@ -508,13 +599,14 @@ rec {
       mkOptionType rec {
         name = "coercedTo";
         description = "${finalType.description} or ${coercedType.description} convertible to it";
-        check = x: finalType.check x || (coercedType.check x && finalType.check (coerceFunc x));
+        check = x: (coercedType.check x && finalType.check (coerceFunc x)) || finalType.check x;
         merge = loc: defs:
           let
             coerceVal = val:
-              if finalType.check val then val
-              else coerceFunc val;
+              if coercedType.check val then coerceFunc val
+              else val;
           in finalType.merge loc (map (def: def // { value = coerceVal def.value; }) defs);
+        emptyValue = finalType.emptyValue;
         getSubOptions = finalType.getSubOptions;
         getSubModules = finalType.getSubModules;
         substSubModules = m: coercedTo coercedType coerceFunc (finalType.substSubModules m);