Allow 'nix' subcommands to provide docs in Markdown format

doc/manual/generate-manpage.jq

@@ -12,7 +12,7 @@ def show_flags:
   ;
 
 def show_synopsis:
-  "`" + .command + "` " + (.args | map("*" + .label + "*" + (if has("arity") then "" else "..." end)) | join(" ")) + "\n\n"
+  "`" + .command + "` [*flags*...] " + (.args | map("*" + .label + "*" + (if has("arity") then "" else "..." end)) | join(" ")) + "\n\n"
   ;
 
 def show_command:
@@ -21,6 +21,10 @@ def show_command:
   + "`" + .command + "` - " + .def.description + "\n\n"
   + .section + " Synopsis\n\n"
   + ({"command": .command, "args": .def.args} | show_synopsis)
+  + (if .def | has("doc")
+     then .section + " Description\n\n" + .def.doc + "\n\n"
+     else ""
+     end)
   + (if (.def.flags | length) > 0 then
       .section + " Flags\n\n"
       + (.def | show_flags)

src/libutil/args.cc

@@ -359,12 +359,14 @@ nlohmann::json Command::toJSON()
     for (auto & example : examples()) {
         auto ex = nlohmann::json::object();
         ex["description"] = example.description;
-        ex["command"] = example.command;
+        ex["command"] = chomp(stripIndentation(example.command));
         exs.push_back(std::move(ex));
     }
 
     auto res = Args::toJSON();
     res["examples"] = std::move(exs);
+    auto s = doc();
+    if (s != "") res.emplace("doc", stripIndentation(s));
     return res;
 }
 

src/libutil/args.hh

@@ -22,6 +22,7 @@ public:
 
     virtual void printHelp(const string & programName, std::ostream & out);
 
+    /* Return a short one-line description of the command. */
     virtual std::string description() { return ""; }
 
 protected:
@@ -221,6 +222,9 @@ struct Command : virtual Args
     virtual void prepare() { };
     virtual void run() = 0;
 
+    /* Return documentation about this command, in Markdown format. */
+    virtual std::string doc() { return ""; }
+
     struct Example
     {
         std::string description;

src/libutil/config.cc

@@ -153,43 +153,6 @@ void Config::convertToArgs(Args & args, const std::string & category)
             s.second.setting->convertToArg(args, category);
 }
 
-static std::string stripIndentation(std::string_view s)
-{
-    size_t minIndent = 10000;
-    size_t curIndent = 0;
-    bool atStartOfLine = true;
-
-    for (auto & c : s) {
-        if (atStartOfLine && c == ' ')
-            curIndent++;
-        else if (c == '\n') {
-            if (atStartOfLine)
-                minIndent = std::max(minIndent, curIndent);
-            curIndent = 0;
-            atStartOfLine = true;
-        } else {
-            if (atStartOfLine) {
-                minIndent = std::min(minIndent, curIndent);
-                atStartOfLine = false;
-            }
-        }
-    }
-
-    std::string res;
-
-    size_t pos = 0;
-    while (pos < s.size()) {
-        auto eol = s.find('\n', pos);
-        if (eol == s.npos) eol = s.size();
-        if (eol - pos > minIndent)
-            res.append(s.substr(pos + minIndent, eol - pos - minIndent));
-        res.push_back('\n');
-        pos = eol + 1;
-    }
-
-    return res;
-}
-
 AbstractSetting::AbstractSetting(
     const std::string & name,
     const std::string & description,

src/libutil/util.cc

@@ -1464,6 +1464,47 @@ string base64Decode(std::string_view s)
 }
 
 
+std::string stripIndentation(std::string_view s)
+{
+    size_t minIndent = 10000;
+    size_t curIndent = 0;
+    bool atStartOfLine = true;
+
+    for (auto & c : s) {
+        if (atStartOfLine && c == ' ')
+            curIndent++;
+        else if (c == '\n') {
+            if (atStartOfLine)
+                minIndent = std::max(minIndent, curIndent);
+            curIndent = 0;
+            atStartOfLine = true;
+        } else {
+            if (atStartOfLine) {
+                minIndent = std::min(minIndent, curIndent);
+                atStartOfLine = false;
+            }
+        }
+    }
+
+    std::string res;
+
+    size_t pos = 0;
+    while (pos < s.size()) {
+        auto eol = s.find('\n', pos);
+        if (eol == s.npos) eol = s.size();
+        if (eol - pos > minIndent)
+            res.append(s.substr(pos + minIndent, eol - pos - minIndent));
+        res.push_back('\n');
+        pos = eol + 1;
+    }
+
+    return res;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
 static Sync<std::pair<unsigned short, unsigned short>> windowSize{{0, 0}};
 
 

src/libutil/util.hh

@@ -464,6 +464,12 @@ string base64Encode(std::string_view s);
 string base64Decode(std::string_view s);
 
 
+/* Remove common leading whitespace from the lines in the string
+   's'. For example, if every line is indented by at least 3 spaces,
+   then we remove 3 spaces from the start of every line. */
+std::string stripIndentation(std::string_view s);
+
+
 /* Get a value for the specified key from an associate container. */
 template <class T>
 std::optional<typename T::mapped_type> get(const T & map, const typename T::key_type & key)

src/nix/add-to-store.cc

@@ -36,6 +36,14 @@ struct CmdAddToStore : MixDryRun, StoreCommand
         return "add a path to the Nix store";
     }
 
+    std::string doc() override
+    {
+        return R"(
+          Copy the file or directory *path* to the Nix store, and
+          print the resulting store path on standard output.
+        )";
+    }
+
     Examples examples() override
     {
         return {