Use a different default template when there are no args.

This eliminates extraneous empty lines when there are no user-defined
args, the default args are disabled, and `after_help` is set.

src/build/app/mod.rs

@@ -2454,6 +2454,11 @@ impl<'help> App<'help> {
         !self.args.is_empty()
     }
 
+    #[inline]
+    pub(crate) fn has_opts(&self) -> bool {
+        self.get_opts_no_heading().count() > 0
+    }
+
     #[inline]
     pub(crate) fn has_flags(&self) -> bool {
         self.get_flags_no_heading().count() > 0

src/output/help.rs

@@ -82,6 +82,12 @@ impl<'help, 'app, 'parser, 'writer> Help<'help, 'app, 'parser, 'writer> {
         {all-args}{after-help}\
     ";
 
+    const DEFAULT_NO_ARGS_TEMPLATE: &'static str = "\
+        {before-help}{bin} {version}\n\
+        {author-with-newline}{about-with-newline}\n\
+        USAGE:\n    {usage}{after-help}\
+    ";
+
     /// Create a new `Help` instance.
     pub(crate) fn new(
         w: HelpWriter<'writer>,
@@ -124,7 +130,16 @@ impl<'help, 'app, 'parser, 'writer> Help<'help, 'app, 'parser, 'writer> {
         } else if let Some(tmpl) = self.parser.app.template {
             self.write_templated_help(tmpl)?;
         } else {
-            self.write_templated_help(Self::DEFAULT_TEMPLATE)?;
+            let flags = self.parser.has_flags();
+            let pos = self.parser.has_positionals();
+            let opts = self.parser.has_opts();
+            let subcmds = self.parser.has_subcommands();
+
+            if flags || opts || pos || subcmds {
+                self.write_templated_help(Self::DEFAULT_TEMPLATE)?;
+            } else {
+                self.write_templated_help(Self::DEFAULT_NO_ARGS_TEMPLATE)?;
+            }
         }
 
         self.none("\n")?;

src/parse/parser.rs

@@ -1790,6 +1790,10 @@ impl<'help, 'app> Parser<'help, 'app> {
         self.app.has_args()
     }
 
+    pub(crate) fn has_opts(&self) -> bool {
+        self.app.has_opts()
+    }
+
     pub(crate) fn has_flags(&self) -> bool {
         self.app.has_flags()
     }