cli: add --no-context-separator flag

--context-separator='' still adds a new line separator, which could
still potentially be useful. So we add a new `--no-context-separator`
flag that completely disables context separators even when the -A/-B/-C
context flags are used.

Closes #1390

src/app.rs

@@ -963,12 +963,27 @@ This overrides both the -B/--before-context and -A/--after-context flags.
 
 fn flag_context_separator(args: &mut Vec<RGArg>) {
     const SHORT: &str = "Set the context separator string.";
-    const LONG: &str = long!("\
-The string used to separate non-contiguous context lines in the output. Escape
+    const LONG: &str = long!(
+        "\
+The string used to separate non-contiguous context lines in the output. This
+is only used when one of the context flags is used (-A, -B or -C). Escape
 sequences like \\x7F or \\t may be used. The default value is --.
-");
+
+When the context separator is set to an empty string, then a line break
+is still inserted. To completely disable context separators, use the
+--no-context-separator flag.
+"
+    );
+
     let arg = RGArg::flag("context-separator", "SEPARATOR")
-        .help(SHORT).long_help(LONG);
+        .help(SHORT)
+        .long_help(LONG)
+        .overrides("no-context-separator");
+    args.push(arg);
+
+    let arg = RGArg::switch("no-context-separator")
+        .hidden()
+        .overrides("context-separator");
     args.push(arg);
 }
 

src/args.rs

@@ -784,7 +784,7 @@ impl ArgMatches {
             .byte_offset(self.is_present("byte-offset"))
             .trim_ascii(self.is_present("trim"))
             .separator_search(None)
-            .separator_context(Some(self.context_separator()))
+            .separator_context(self.context_separator())
             .separator_field_match(b":".to_vec())
             .separator_field_context(b"-".to_vec())
             .separator_path(self.path_separator()?)
@@ -1020,10 +1020,14 @@ impl ArgMatches {
     /// Returns the unescaped context separator in UTF-8 bytes.
     ///
     /// If one was not provided, the default `--` is returned.
-    fn context_separator(&self) -> Vec<u8> {
-        match self.value_of_os("context-separator") {
-            None => b"--".to_vec(),
-            Some(sep) => cli::unescape_os(&sep),
+    /// If --no-context-separator is passed, None is returned.
+    fn context_separator(&self) -> Option<Vec<u8>> {
+        let nosep = self.is_present("no-context-separator");
+        let sep = self.value_of_os("context-separator");
+        match (nosep, sep) {
+            (true, _) => None,
+            (false, None) => Some(b"--".to_vec()),
+            (false, Some(sep)) => Some(cli::unescape_os(&sep)),
         }
     }
 
@@ -1092,7 +1096,7 @@ impl ArgMatches {
         Ok(if self.heading() {
             Some(b"".to_vec())
         } else if ctx_before > 0 || ctx_after > 0 {
-            Some(self.context_separator().clone())
+            self.context_separator()
         } else {
             None
         })