home-manager: add news sub-command

This command allows the user to examine the news items generated by
the news module. See #52.

Many thanks to @nonsequitur and @uvNikita for suggestions and
improvements.

home-manager/default.nix

@@ -23,6 +23,7 @@ pkgs.stdenv.mkDerivation {
     substituteInPlace $out/bin/home-manager \
       --subst-var-by bash "${pkgs.bash}" \
       --subst-var-by coreutils "${pkgs.coreutils}" \
+      --subst-var-by less "${pkgs.less}" \
       --subst-var-by MODULES_PATH '${modulesPathStr}' \
       --subst-var-by HOME_MANAGER_EXPR_PATH "${./home-manager.nix}"
   '';

home-manager/home-manager

@@ -3,12 +3,12 @@
 # This code explicitly requires GNU Core Utilities and we therefore
 # need to ensure they are prioritized over any other similarly named
 # tools on the system.
-PATH=@coreutils@/bin:$PATH
+PATH=@coreutils@/bin:@less@/bin${PATH:+:}$PATH
 
 set -euo pipefail
 
 function errorEcho() {
-    >&2 echo "$*"
+    echo $* >&2
 }
 
 # Attempts to set the HOME_MANAGER_CONFIG global variable.
@@ -52,12 +52,11 @@ function setHomeManagerModulesPath() {
     done
 }
 
-function doBuild() {
+function doBuildAttr() {
     setConfigFile
     setHomeManagerModulesPath
 
-    local extraArgs
+    local extraArgs="$*"
-    extraArgs="$1"
 
     for p in "${EXTRA_NIX_PATH[@]}"; do
         extraArgs="$extraArgs -I $p"
@@ -67,11 +66,53 @@ function doBuild() {
         extraArgs="$extraArgs --show-trace"
     fi
 
-    nix-build $extraArgs \
+    nix-build \
-              "@HOME_MANAGER_EXPR_PATH@" \
+        "@HOME_MANAGER_EXPR_PATH@" \
-              --argstr confPath "$HOME_MANAGER_CONFIG" \
+        $extraArgs \
-              --argstr confAttr "$HOME_MANAGER_CONFIG_ATTRIBUTE" \
+        --argstr confPath "$HOME_MANAGER_CONFIG" \
-              -A activationPackage
+        --argstr confAttr "$HOME_MANAGER_CONFIG_ATTRIBUTE"
+}
+
+function presentNews() {
+    local infoFile
+    infoFile=$(doBuildNews -A newsInfo) || return 1
+
+    # shellcheck source=/dev/null
+    . "$infoFile"
+
+    if [[ $newsNumUnread -eq 0 ]]; then
+        return
+    elif [[ "$newsDisplay" == "silent" ]]; then
+        return
+    elif [[ "$newsDisplay" == "notify" ]]; then
+        local msg
+        if [[ $newsNumUnread -eq 1 ]]; then
+            msg="There is an unread and relevant news item.\n"
+            msg+="Read it by running the command '$(basename "$0") news'."
+        else
+            msg="There are $newsNumUnread unread and relevant news items.\n"
+            msg+="Read them by running the command '$(basename "$0") news'."
+        fi
+
+        # Not actually an error but here stdout is reserved for
+        # nix-build output.
+        errorEcho
+        errorEcho -e "$msg"
+        errorEcho
+
+        if [[ -v DISPLAY ]] && type -P notify-send > /dev/null; then
+            notify-send "Home Manager" "$msg"
+        fi
+    elif [[ "$newsDisplay" == "show" ]]; then
+        doShowNews --unread
+    else
+        errorEcho "Unknown 'news.display' setting '$newsDisplay'."
+    fi
+}
+
+function doBuild() {
+    doBuildAttr -A activationPackage
+    presentNews
 }
 
 function doSwitch() {
@@ -84,12 +125,17 @@ function doSwitch() {
     # prevents an unfortunately timed GC from removing the generation
     # before activation completes.
     wrkdir="$(mktemp -d)"
-    generation=$(doBuild "-o $wrkdir/result") && $generation/activate || exitCode=1
+    generation=$(doBuildAttr -o "$wrkdir/result" -A activationPackage) \
+        && $generation/activate || exitCode=1
 
     # Because the previous command never fails, the script keeps
     # running and $wrkdir is always removed.
     rm -r "$wrkdir"
 
+    if [[ $exitCode -eq 0 ]]; then
+        presentNews
+    fi
+
     return $exitCode
 }
 
@@ -110,6 +156,53 @@ function doListPackages() {
     fi
 }
 
+function newsReadIdsFile() {
+    local dataDir="${XDG_DATA_HOME:-$HOME/.local/share}/home-manager"
+    local path="$dataDir/news-read-ids"
+
+    # If the path doesn't exist then we should create it, otherwise
+    # Nix will error out when we attempt to use builtins.readFile.
+    if [[ ! -f "$path" ]]; then
+        mkdir -p "$dataDir"
+        touch "$path"
+    fi
+
+    echo "$path"
+}
+
+function doBuildNews() {
+    doBuildAttr "$*" \
+                --no-out-link \
+                --arg check false \
+                --argstr newsReadIdsFile "$(newsReadIdsFile)"
+}
+
+function doShowNews() {
+    local infoFile
+    infoFile=$(doBuildNews -A newsInfo) || return 1
+
+    # shellcheck source=/dev/null
+    . "$infoFile"
+
+    case $1 in
+        --all)
+            ${PAGER:-less} "$newsFileAll"
+            ;;
+        --unread)
+            ${PAGER:-less} "$newsFileUnread"
+            ;;
+        *)
+            errorEcho "Unknown argument $1"
+            return 1
+    esac
+
+    if [[ -s "$newsUnreadIdsFile" ]]; then
+        local newsReadIdsFile
+        newsReadIdsFile="$(newsReadIdsFile)"
+        cat "$newsUnreadIdsFile" >> "$newsReadIdsFile"
+    fi
+}
+
 function doHelp() {
     echo "Usage: $0 [OPTION] COMMAND"
     echo
@@ -130,6 +223,7 @@ function doHelp() {
     echo "  switch       Build and activate configuration"
     echo "  generations  List all home environment generations"
     echo "  packages     List all packages installed in home-manager-path"
+    echo "  news         Show news entries in a pager"
 }
 
 EXTRA_NIX_PATH=()
@@ -171,7 +265,7 @@ cmd="$*"
 
 case "$cmd" in
     build)
-        doBuild ""
+        doBuild
         ;;
     switch)
         doSwitch
@@ -182,6 +276,9 @@ case "$cmd" in
     packages)
         doListPackages
         ;;
+    news)
+        doShowNews --all
+        ;;
     help|--help)
         doHelp
         ;;

home-manager/home-manager.nix

@@ -1,6 +1,14 @@
-{ pkgs ? import <nixpkgs> {}, confPath, confAttr }:
+{ pkgs ? import <nixpkgs> {}
+, confPath
+, confAttr
+, check ? true
+, newsReadIdsFile ? null
+}:
+
+with pkgs.lib;
 
 let
+
   env = import <home-manager> {
     configuration =
       let
@@ -8,8 +16,74 @@ let
       in
         if confAttr == "" then conf else conf.${confAttr};
     pkgs = pkgs;
+    check = check;
   };
+
+  newsReadIds =
+    if newsReadIdsFile == null
+    then {}
+    else
+      let
+        ids = splitString "\n" (fileContents newsReadIdsFile);
+      in
+        builtins.listToAttrs (map (id: { name = id; value = null; }) ids);
+
+  newsIsRead = entry: builtins.hasAttr entry.id newsReadIds;
+
+  newsFiltered =
+    let
+      pred = entry: entry.condition && ! newsIsRead entry;
+    in
+      filter pred env.newsEntries;
+
+  newsNumUnread = length newsFiltered;
+
+  newsFileUnread = pkgs.writeText "news-unread.txt" (
+    concatMapStringsSep "\n\n" (entry:
+      let
+        time = replaceStrings ["T"] [" "] (removeSuffix "+00:00" entry.time);
+      in
+        ''
+          * ${time}
+
+            ${replaceStrings ["\n"] ["\n  "] entry.message}
+        ''
+    ) newsFiltered
+  );
+
+  newsFileAll = pkgs.writeText "news-all.txt" (
+    concatMapStringsSep "\n\n" (entry:
+      let
+        flag = if newsIsRead entry then "read" else "unread";
+        time = replaceStrings ["T"] [" "] (removeSuffix "+00:00" entry.time);
+      in
+        ''
+          * ${time} [${flag}]
+
+            ${replaceStrings ["\n"] ["\n  "] entry.message}
+        ''
+    ) env.newsEntries
+  );
+
+  # File where each line corresponds to an unread news entry
+  # identifier. If non-empty then the file ends in "\n".
+  newsUnreadIdsFile = pkgs.writeText "news-unread-ids" (
+    let
+      text = concatMapStringsSep "\n" (entry: entry.id) newsFiltered;
+    in
+      text + optionalString (text != "") "\n"
+  );
+
+  newsInfo = pkgs.writeText "news-info.sh" ''
+    local newsNumUnread=${toString newsNumUnread}
+    local newsDisplay="${env.newsDisplay}"
+    local newsFileAll="${newsFileAll}"
+    local newsFileUnread="${newsFileUnread}"
+    local newsUnreadIdsFile="${newsUnreadIdsFile}"
+  '';
+
 in
   {
     inherit (env) activationPackage;
+    inherit newsInfo;
   }

modules/default.nix

@@ -1,6 +1,9 @@
 { configuration
 , pkgs
 , lib ? pkgs.stdenv.lib
+
+  # Whether to check that each option has a matching declaration.
+, check ? true
 }:
 
 with lib;
@@ -64,6 +67,7 @@ let
   pkgsModule = {
     config._module.args.pkgs = lib.mkForce pkgs;
     config._module.args.baseModules = modules;
+    config._module.check = check;
   };
 
   module = showWarnings (
@@ -90,4 +94,10 @@ in
 
   # For backwards compatibility. Please use activationPackage instead.
   activation-script = module.config.home.activationPackage;
+
+  newsDisplay = module.config.news.display;
+  newsEntries =
+    sort (a: b: a.time > b.time) (
+      filter (a: a.condition) module.config.news.entries
+    );
 }