Use minus as a builtin pager

CHANGELOG.md

@@ -35,11 +35,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `jj next/prev` now infer `--edit` when you're already editing a non-head
   commit (a commit with children).
 
+* Built-in pager based on [minus](https://github.com/arijit79/minus/)
+
 ### Fixed bugs
 
 * On Windows, symlinks in the repo are now materialized as regular files in the
   working copy (instead of resulting in a crash).
 
+* On Windows, the pager will now be the built-in instead of disabled.
+
 ## [0.14.0] - 2024-02-07
 
 ### Deprecations

Cargo.lock

@@ -1620,6 +1620,7 @@ dependencies = [
  "jj-lib",
  "libc",
  "maplit",
+ "minus",
  "once_cell",
  "pest",
  "pest_derive",
@@ -1858,6 +1859,21 @@ dependencies = [
  "adler",
 ]
 
+[[package]]
+name = "minus"
+version = "5.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14b5f31d6666667f707078608f25e7615c48c2243a06b66ca0fa6c4ecb96362d"
+dependencies = [
+ "crossbeam-channel",
+ "crossterm",
+ "once_cell",
+ "parking_lot",
+ "regex",
+ "textwrap",
+ "thiserror",
+]
+
 [[package]]
 name = "mio"
 version = "0.8.10"
@@ -1938,6 +1954,9 @@ name = "once_cell"
 version = "1.19.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
+dependencies = [
+ "parking_lot_core",
+]
 
 [[package]]
 name = "oorandom"

Cargo.toml

@@ -58,6 +58,7 @@ insta = { version = "1.34.0", features = ["filters"] }
 itertools = "0.12.1"
 libc = { version = "0.2.153" }
 maplit = "1.0.2"
+minus = { version = "5.5.0", features = [ "dynamic_output", "search" ] }
 num_cpus = "1.16.0"
 once_cell = "1.19.0"
 ouroboros = "0.18.0"

cli/Cargo.toml

@@ -52,6 +52,7 @@ indexmap = { workspace = true }
 itertools = { workspace = true }
 jj-lib = { workspace = true }
 maplit = { workspace = true }
+minus = { workspace = true }
 once_cell = { workspace = true }
 pest = { workspace = true }
 pest_derive = { workspace = true }

cli/src/config/windows.toml

@@ -1,3 +1,3 @@
 [ui]
-paginate = "never"
+pager = ":builtin"
 editor = "Notepad"

cli/src/ui.rs

@@ -15,14 +15,18 @@
 use std::io::{IsTerminal as _, Stderr, StderrLock, Stdout, StdoutLock, Write};
 use std::process::{Child, ChildStdin, Stdio};
 use std::str::FromStr;
+use std::thread::JoinHandle;
 use std::{env, fmt, io, mem};
 
+use minus::Pager as MinusPager;
 use tracing::instrument;
 
 use crate::cli_util::CommandError;
 use crate::config::CommandNameAndArgs;
 use crate::formatter::{Formatter, FormatterFactory, LabeledWriter};
 
+const BUILTIN_PAGER_NAME: &str = ":builtin";
+
 enum UiOutput {
     Terminal {
         stdout: Stdout,
@@ -32,9 +36,67 @@ enum UiOutput {
         child: Child,
         child_stdin: ChildStdin,
     },
+    BuiltinPaged {
+        pager: BuiltinPager,
+    },
+}
+
+/// A builtin pager
+pub struct BuiltinPager {
+    pager: MinusPager,
+    dynamic_pager_thread: JoinHandle<()>,
+}
+
+impl std::io::Write for &BuiltinPager {
+    fn flush(&mut self) -> io::Result<()> {
+        // no-op since this is being run in a dynamic pager mode.
+        Ok(())
+    }
+
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let string = std::str::from_utf8(buf).map_err(std::io::Error::other)?;
+        self.pager.push_str(string).map_err(std::io::Error::other)?;
+        Ok(buf.len())
+    }
+}
+
+impl Default for BuiltinPager {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl BuiltinPager {
+    pub fn finalize(self) {
+        let dynamic_pager_thread = self.dynamic_pager_thread;
+        dynamic_pager_thread.join().unwrap();
+    }
+
+    pub fn new() -> Self {
+        let pager = MinusPager::new();
+        // Prefer to be cautious and only kill the pager instead of the whole process
+        // like minus does by default.
+        pager
+            .set_exit_strategy(minus::ExitStrategy::PagerQuit)
+            .expect("Able to set the exit strategy");
+        let pager_handle = pager.clone();
+
+        BuiltinPager {
+            pager,
+            dynamic_pager_thread: std::thread::spawn(move || {
+                // This thread handles the actual paging.
+                minus::dynamic_paging(pager_handle).unwrap();
+            }),
+        }
+    }
 }
 
 impl UiOutput {
+    fn new_builtin() -> UiOutput {
+        UiOutput::BuiltinPaged {
+            pager: BuiltinPager::new(),
+        }
+    }
     fn new_terminal() -> UiOutput {
         UiOutput::Terminal {
             stdout: io::stdout(),
@@ -49,16 +111,16 @@ impl UiOutput {
     }
 }
 
-#[derive(Debug)]
 pub enum UiStdout<'a> {
     Terminal(StdoutLock<'static>),
     Paged(&'a ChildStdin),
+    Builtin(&'a BuiltinPager),
 }
 
-#[derive(Debug)]
 pub enum UiStderr<'a> {
     Terminal(StderrLock<'static>),
     Paged(&'a ChildStdin),
+    Builtin(&'a BuiltinPager),
 }
 
 macro_rules! for_outputs {
@@ -66,6 +128,7 @@ macro_rules! for_outputs {
         match $output {
             $ty::Terminal($pat) => $expr,
             $ty::Paged($pat) => $expr,
+            $ty::Builtin($pat) => $expr,
         }
     };
 }
@@ -217,6 +280,11 @@ impl Ui {
 
         match self.output {
             UiOutput::Terminal { .. } if io::stdout().is_terminal() => {
+                if self.pager_cmd == CommandNameAndArgs::String(BUILTIN_PAGER_NAME.into()) {
+                    self.output = UiOutput::new_builtin();
+                    return;
+                }
+
                 match UiOutput::new_paged(&self.pager_cmd) {
                     Ok(pager_output) => {
                         self.output = pager_output;
@@ -225,14 +293,15 @@ impl Ui {
                         // The pager executable couldn't be found or couldn't be run
                         writeln!(
                             self.warning(),
-                            "Failed to spawn pager '{name}': {e}",
+                            "Failed to spawn pager '{name}': {e}. Consider using the `:builtin` \
+                             pager.",
                             name = self.pager_cmd.split_name(),
                         )
                         .ok();
                     }
                 }
             }
-            UiOutput::Terminal { .. } | UiOutput::Paged { .. } => {}
+            UiOutput::Terminal { .. } | UiOutput::BuiltinPaged { .. } | UiOutput::Paged { .. } => {}
         }
     }
 
@@ -252,6 +321,7 @@ impl Ui {
         match &self.output {
             UiOutput::Terminal { stdout, .. } => UiStdout::Terminal(stdout.lock()),
             UiOutput::Paged { child_stdin, .. } => UiStdout::Paged(child_stdin),
+            UiOutput::BuiltinPaged { pager } => UiStdout::Builtin(pager),
         }
     }
 
@@ -268,6 +338,7 @@ impl Ui {
         match &self.output {
             UiOutput::Terminal { stderr, .. } => UiStderr::Terminal(stderr.lock()),
             UiOutput::Paged { child_stdin, .. } => UiStderr::Paged(child_stdin),
+            UiOutput::BuiltinPaged { pager } => UiStderr::Builtin(pager),
         }
     }
 
@@ -281,6 +352,8 @@ impl Ui {
         match &self.output {
             UiOutput::Terminal { .. } => Ok(Stdio::inherit()),
             UiOutput::Paged { child_stdin, .. } => Ok(duplicate_child_stdin(child_stdin)?.into()),
+            // Stderr does not get redirected through the built-in pager.
+            UiOutput::BuiltinPaged { .. } => Ok(Stdio::inherit()),
         }
     }
 
@@ -290,6 +363,7 @@ impl Ui {
         match &self.output {
             UiOutput::Terminal { stderr, .. } => self.progress_indicator && stderr.is_terminal(),
             UiOutput::Paged { .. } => false,
+            UiOutput::BuiltinPaged { .. } => false,
         }
     }
 
@@ -314,11 +388,11 @@ impl Ui {
     /// Waits for the pager exits.
     #[instrument(skip_all)]
     pub fn finalize_pager(&mut self) {
-        if let UiOutput::Paged {
+        match mem::replace(&mut self.output, UiOutput::new_terminal()) {
+            UiOutput::Paged {
                 mut child,
                 child_stdin,
-        } = mem::replace(&mut self.output, UiOutput::new_terminal())
-        {
+            } => {
                 drop(child_stdin);
                 if let Err(e) = child.wait() {
                     // It's possible (though unlikely) that this write fails, but
@@ -327,6 +401,11 @@ impl Ui {
                     writeln!(self.error(), "Failed to wait on pager: {e}").ok();
                 }
             }
+            UiOutput::BuiltinPaged { pager } => {
+                pager.finalize();
+            }
+            _ => { /* no-op */ }
+        }
     }
 
     pub fn can_prompt() -> bool {

docs/config.md

@@ -300,16 +300,26 @@ Can be customized by the `format_short_signature()` template alias.
 
 ## Pager
 
-Windows users: Note that pagination is disabled by default on Windows for now
-([#2040](https://github.com/martinvonz/jj/issues/2040)).
-
 The default pager is can be set via `ui.pager` or the `PAGER` environment
 variable. The priority is as follows (environment variables are marked with
 a `$`):
 
 `ui.pager` > `$PAGER`
 
-`less -FRX` is the default pager in the absence of any other setting.
+`less -FRX` is the default pager in the absence of any other setting, except
+on Windows where it is `:builtin`.
+
+The special value `:builtin` enables usage of the
+[integrated pager](https://github.com/arijit79/minus/). It is likely if you
+are using a standard Linux distro, your system has `$PAGER` set already
+and that will be preferred over the built-in. To use the built-in:
+
+```
+jj config set --user ui.pager :builtin
+```
+
+It is possible the default will change to `:builtin` for all platforms in the
+future.
 
 Additionally, paging behavior can be toggled via `ui.paginate` like so: