From 5972f66ef6b2a845661f04b7064c5eb29f89788e Mon Sep 17 00:00:00 2001
From: ath3 <ha05190@protonmail.com>
Date: Thu, 25 Nov 2021 15:34:46 +0100
Subject: [PATCH] Implement black hole register

---
 book/src/usage.md           |  2 ++
 helix-core/src/register.rs  | 40 ++++++++++++++++++++++++++-----------
 helix-term/src/commands.rs  |  7 ++++---
 helix-term/src/ui/prompt.rs | 19 ++++++++++--------
 4 files changed, 45 insertions(+), 23 deletions(-)

diff --git a/book/src/usage.md b/book/src/usage.md
index 6b7cbc415e5c4..cf7d9d488309a 100644
--- a/book/src/usage.md
+++ b/book/src/usage.md
@@ -23,8 +23,10 @@ If there is a selected register before invoking a change or delete command, the
 | `/`                | Last search           |
 | `:`                | Last executed command |
 | `"`                | Last yanked text      |
+| `_`                | Black hole            |
 
 > There is no special register for copying to system clipboard, instead special commands and keybindings are provided. See the [keymap](keymap.md#space-mode) for the specifics.
+> The black hole register works as a no-op register, meaning no data will be written to / read from it.
 
 ## Surround
 
diff --git a/helix-core/src/register.rs b/helix-core/src/register.rs
index c5444eb73856a..439ccddd349d7 100644
--- a/helix-core/src/register.rs
+++ b/helix-core/src/register.rs
@@ -7,15 +7,23 @@ pub struct Register {
 }
 
 impl Register {
-    pub const fn new(name: char) -> Self {
-        Self {
-            name,
-            values: Vec::new(),
+    pub const fn new(name: char) -> Option<Self> {
+        if name != '_' {
+            Some(Self {
+                name,
+                values: Vec::new(),
+            })
+        } else {
+            None
         }
     }
 
-    pub fn new_with_values(name: char, values: Vec<String>) -> Self {
-        Self { name, values }
+    pub fn new_with_values(name: char, values: Vec<String>) -> Option<Self> {
+        if name != '_' {
+            Some(Self { name, values })
+        } else {
+            None
+        }
     }
 
     pub const fn name(&self) -> char {
@@ -46,15 +54,23 @@ impl Registers {
         self.inner.get(&name)
     }
 
-    pub fn get_mut(&mut self, name: char) -> &mut Register {
-        self.inner
-            .entry(name)
-            .or_insert_with(|| Register::new(name))
+    pub fn get_mut(&mut self, name: char) -> Option<&mut Register> {
+        if name != '_' {
+            Some(
+                self.inner
+                    .entry(name)
+                    .or_insert_with(|| Register::new(name).unwrap()),
+            )
+        } else {
+            None
+        }
     }
 
     pub fn write(&mut self, name: char, values: Vec<String>) {
-        self.inner
-            .insert(name, Register::new_with_values(name, values));
+        if name != '_' {
+            self.inner
+                .insert(name, Register::new_with_values(name, values).unwrap());
+        }
     }
 
     pub fn read(&self, name: char) -> Option<&[String]> {
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index ff8d7a4ffe83a..7243ce933d7aa 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -1503,7 +1503,7 @@ fn search_selection(cx: &mut Context) {
     let contents = doc.text().slice(..);
     let query = doc.selection(view.id).primary().fragment(contents);
     let regex = regex::escape(&query);
-    cx.editor.registers.get_mut('/').push(regex);
+    cx.editor.registers.get_mut('/').unwrap().push(regex);
     let msg = format!("register '{}' set to '{}'", '\\', query);
     cx.editor.set_status(msg);
 }
@@ -1710,8 +1710,9 @@ fn delete_selection_impl(cx: &mut Context, op: Operation) {
         let values: Vec<String> = selection.fragments(text).map(Cow::into_owned).collect();
         let reg_name = cx.register.unwrap_or('"');
         let registers = &mut cx.editor.registers;
-        let reg = registers.get_mut(reg_name);
-        reg.write(values);
+        if let Some(reg) = registers.get_mut(reg_name) {
+            reg.write(values);
+        }
     };
 
     // then delete
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index e90b0772785ea..04043fc524a18 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -481,24 +481,27 @@ impl Component for Prompt {
 
                     if let Some(register) = self.history_register {
                         // store in history
-                        let register = cx.editor.registers.get_mut(register);
-                        register.push(self.line.clone());
+                        if let Some(register) = cx.editor.registers.get_mut(register) {
+                            register.push(self.line.clone());
+                        }
                     }
                     return close_fn;
                 }
             }
             ctrl!('p') | key!(Up) => {
                 if let Some(register) = self.history_register {
-                    let register = cx.editor.registers.get_mut(register);
-                    self.change_history(register.read(), CompletionDirection::Backward);
-                    (self.callback_fn)(cx, &self.line, PromptEvent::Update);
+                    if let Some(register) = cx.editor.registers.get_mut(register) {
+                        self.change_history(register.read(), CompletionDirection::Backward);
+                        (self.callback_fn)(cx, &self.line, PromptEvent::Update);
+                    }
                 }
             }
             ctrl!('n') | key!(Down) => {
                 if let Some(register) = self.history_register {
-                    let register = cx.editor.registers.get_mut(register);
-                    self.change_history(register.read(), CompletionDirection::Forward);
-                    (self.callback_fn)(cx, &self.line, PromptEvent::Update);
+                    if let Some(register) = cx.editor.registers.get_mut(register) {
+                        self.change_history(register.read(), CompletionDirection::Forward);
+                        (self.callback_fn)(cx, &self.line, PromptEvent::Update);
+                    }
                 }
             }
             key!(Tab) => {