Allow running polybar without BAR argument (#2526)

* Allow running polybar without BAR argument

The configuration file must declare a single bar to be able to not name
it.

* Check barname not in config and improve error message

* Revert README changes

* Add no bar in config file error detection

CHANGELOG.md

@@ -159,6 +159,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Increased the double click interval from 150ms to 400ms.
 - Stop ignoring actions if they arrive while the previous one hasn't been processed yet.
   ([`#2469`](https://github.com/polybar/polybar/issues/2469))
+- Polybar can now be run without passing the bar name as argument given that 
+  the configuration file only defines one bar
+  ([`#2525`](https://github.com/polybar/polybar/issues/2525))
 
 ### Fixed
 - `custom/script`: Concurrency issues with fast-updating tailed scripts.

doc/man/polybar.1.rst

@@ -3,11 +3,12 @@ polybar(1)
 
 SYNOPSIS
 --------
-**polybar** [*OPTIONS*]... *BAR*
+**polybar** [*OPTIONS*]... [*BAR*]
 
 DESCRIPTION
 -----------
 Polybar aims to help users build beautiful and highly customizable status bars for their desktop environment, without the need of having a black belt in shell scripting.
+If the *BAR* argument is not provided and the configuration file only contains one bar definition, Polybar will display this bar.
 
 OPTIONS
 -------

include/components/config.hpp

@@ -33,6 +33,8 @@ class config {
   const string& filepath() const;
   string section() const;
 
+  static constexpr const char* BAR_PREFIX = "bar/";
+
   /**
    * \brief Instruct the config to connect to the xresource manager
    */

include/components/config_parser.hpp

@@ -215,6 +215,8 @@ class config_parser {
    */
   bool is_valid_name(const string& name);
 
+  vector<string> get_bars(const sectionmap_t& sections) const;
+
   /**
    * \brief Whether or not an xresource manager should be used
    *

src/components/command_line.cpp

@@ -9,7 +9,7 @@ namespace command_line {
    * Create instance
    */
   parser::make_type parser::make(string&& scriptname, const options&& opts) {
-    return std::make_unique<parser>("Usage: " + scriptname + " [OPTION]... BAR", forward<decltype(opts)>(opts));
+    return std::make_unique<parser>("Usage: " + scriptname + " [OPTION]... [BAR]", forward<decltype(opts)>(opts));
   }
 
   /**

src/components/config.cpp

@@ -31,7 +31,7 @@ const string& config::filepath() const {
  * Get the section name of the bar in use
  */
 string config::section() const {
-  return "bar/" + m_barname;
+  return BAR_PREFIX + m_barname;
 }
 
 void config::use_xrm() {

src/components/config_parser.cpp

@@ -20,8 +20,23 @@ config::make_type config_parser::parse() {
 
   sectionmap_t sections = create_sectionmap();
 
-  if (sections.find("bar/" + m_barname) == sections.end()) {
-    throw application_error("Undefined bar: " + m_barname);
+  vector<string> bars = get_bars(sections);
+  if (m_barname.empty()) {
+    if (bars.size() == 1) {
+      m_barname = bars[0];
+    } else if (bars.empty()) {
+      throw application_error("The config file contains no bar.");
+    } else {
+      throw application_error("The config file contains multiple bars, but no bar name was given. Available bars: " +
+                              string_util::join(bars, ", "));
+    }
+  } else if (sections.find("bar/" + m_barname) == sections.end()) {
+    if (bars.empty()) {
+      throw application_error("Undefined bar: " + m_barname + ". The config file contains no bar.");
+    } else {
+      throw application_error(
+          "Undefined bar: " + m_barname + ". Available bars: " + string_util::join(get_bars(sections), ", "));
+    }
   }
 
   /*
@@ -80,6 +95,19 @@ sectionmap_t config_parser::create_sectionmap() {
   return sections;
 }
 
+/**
+ * Get the bars declared
+ */
+vector<string> config_parser::get_bars(const sectionmap_t& sections) const {
+  vector<string> bars;
+  for (const auto& it : sections) {
+    if (it.first.find(config::BAR_PREFIX) == 0) {
+      bars.push_back(it.first.substr(strlen(config::BAR_PREFIX)));
+    }
+  }
+  return bars;
+}
+
 void config_parser::parse_file(const string& file, file_list path) {
   if (std::find(path.begin(), path.end(), file) != path.end()) {
     string path_str{};

src/main.cpp

@@ -98,10 +98,7 @@ int main(int argc, char** argv) {
     string confpath;
 
     // Make sure a bar name is passed in
-    if (!cli->has(0)) {
-      cli->usage();
-      return EXIT_FAILURE;
-    } else if (cli->has(1)) {
+    if (cli->has(1)) {
       fprintf(stderr, "Unrecognized argument \"%s\"\n", cli->get(1).c_str());
       cli->usage();
       return EXIT_FAILURE;
@@ -123,7 +120,12 @@ int main(int argc, char** argv) {
       throw application_error("Define configuration using --config=PATH");
     }
 
-    config_parser parser{logger, move(confpath), cli->get(0)};
+    string barname;
+    if (cli->has(0)) {
+      barname = cli->get(0);
+    }
+
+    config_parser parser{logger, move(confpath), move(barname)};
     config::make_type conf = parser.parse();
 
     //==================================================