From 30e37c7f6e3e69fefc709b6be5bcfb3a647909fc Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Sat, 15 Jan 2022 15:26:56 -0500
Subject: implement `cd -`

---
 src/env.rs                 | 75 +++++++++++++++++++++++++++++++++++++---------
 src/prelude.rs             |  2 +-
 src/runner/builtins/mod.rs | 26 ++++++++++++++--
 3 files changed, 85 insertions(+), 18 deletions(-)

diff --git a/src/env.rs b/src/env.rs
index 6ac67f5..bf6cb6c 100644
--- a/src/env.rs
+++ b/src/env.rs
@@ -16,6 +16,11 @@ pub struct V0 {
     )]
     latest_status: async_std::process::ExitStatus,
     pwd: std::path::PathBuf,
+    #[serde(
+        serialize_with = "serialize_prev_pwd",
+        deserialize_with = "deserialize_prev_pwd"
+    )]
+    prev_pwd: crate::mutex::Mutex<std::path::PathBuf>,
     vars: std::collections::HashMap<std::ffi::OsString, std::ffi::OsString>,
 }
 
@@ -27,10 +32,12 @@ impl Env {
         > = std::env::vars_os().collect();
         vars.insert("SHELL".into(), std::env::current_exe()?.into());
         vars.insert("TERM".into(), "screen".into());
+        let pwd = std::env::current_dir()?;
         Ok(Self::V0(V0 {
             idx: 0,
             latest_status: std::process::ExitStatus::from_raw(0),
-            pwd: std::env::current_dir()?,
+            pwd: pwd.clone(),
+            prev_pwd: crate::mutex::new(pwd),
             vars,
         }))
     }
@@ -67,14 +74,6 @@ impl Env {
         }
     }
 
-    pub fn set_current_dir(&mut self, pwd: std::path::PathBuf) {
-        match self {
-            Self::V0(env) => {
-                env.pwd = pwd;
-            }
-        }
-    }
-
     pub fn var(&self, k: &str) -> String {
         match self {
             Self::V0(env) => self.special_var(k).unwrap_or_else(|| {
@@ -94,13 +93,16 @@ impl Env {
         }
     }
 
-    pub fn set_vars(
-        &mut self,
-        it: impl Iterator<Item = (std::ffi::OsString, std::ffi::OsString)>,
-    ) {
+    pub async fn prev_pwd(&self) -> std::path::PathBuf {
+        match self {
+            Self::V0(env) => env.prev_pwd.lock_arc().await.clone(),
+        }
+    }
+
+    pub async fn set_prev_pwd(&self, prev_pwd: &std::path::Path) {
         match self {
             Self::V0(env) => {
-                env.vars = it.collect();
+                *env.prev_pwd.lock_arc().await = prev_pwd.to_path_buf();
             }
         }
     }
@@ -151,6 +153,25 @@ impl Env {
             }),
         }
     }
+
+    fn set_current_dir(&mut self, pwd: std::path::PathBuf) {
+        match self {
+            Self::V0(env) => {
+                env.pwd = pwd;
+            }
+        }
+    }
+
+    fn set_vars(
+        &mut self,
+        it: impl Iterator<Item = (std::ffi::OsString, std::ffi::OsString)>,
+    ) {
+        match self {
+            Self::V0(env) => {
+                env.vars = it.collect();
+            }
+        }
+    }
 }
 
 #[allow(clippy::trivially_copy_pass_by_ref)]
@@ -175,3 +196,29 @@ where
     let status = u16::deserialize(d)?;
     Ok(std::process::ExitStatus::from_raw(i32::from(status)))
 }
+
+#[allow(clippy::trivially_copy_pass_by_ref)]
+fn serialize_prev_pwd<S>(
+    prev_pwd: &crate::mutex::Mutex<std::path::PathBuf>,
+    s: S,
+) -> Result<S::Ok, S::Error>
+where
+    S: serde::Serializer,
+{
+    s.serialize_bytes(
+        async_std::task::block_on(async { prev_pwd.lock_arc().await })
+            .as_os_str()
+            .as_bytes(),
+    )
+}
+
+fn deserialize_prev_pwd<'de, D>(
+    d: D,
+) -> Result<crate::mutex::Mutex<std::path::PathBuf>, D::Error>
+where
+    D: serde::Deserializer<'de>,
+{
+    Ok(crate::mutex::new(std::path::PathBuf::from(
+        std::ffi::OsString::from_vec(Vec::deserialize(d)?),
+    )))
+}
diff --git a/src/prelude.rs b/src/prelude.rs
index 8c888c8..6789a1f 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -5,7 +5,7 @@ pub use async_std::stream::StreamExt as _;
 pub use futures_lite::future::FutureExt as _;
 
 pub use async_std::os::unix::process::CommandExt as _;
-pub use std::os::unix::ffi::OsStrExt as _;
+pub use std::os::unix::ffi::{OsStrExt as _, OsStringExt as _};
 pub use std::os::unix::io::{AsRawFd as _, FromRawFd as _, IntoRawFd as _};
 pub use std::os::unix::process::ExitStatusExt as _;
 pub use users::os::unix::UserExt as _;
diff --git a/src/runner/builtins/mod.rs b/src/runner/builtins/mod.rs
index ff03499..c345a85 100644
--- a/src/runner/builtins/mod.rs
+++ b/src/runner/builtins/mod.rs
@@ -65,7 +65,9 @@ fn cd(
     ) -> std::process::ExitStatus {
         let dir = if let Some(dir) = exe.args().get(0) {
             if dir.is_empty() {
-                ".".to_string()
+                ".".to_string().into()
+            } else if dir == "-" {
+                env.prev_pwd().await
             } else {
                 dir.into()
             }
@@ -74,11 +76,29 @@ fn cd(
             if dir.is_empty() {
                 bail!(cfg, exe, "could not find home directory");
             }
-            dir
+            dir.into()
+        };
+        let prev = match std::env::current_dir() {
+            Ok(path) => path,
+            Err(e) => {
+                bail!(
+                    cfg,
+                    exe,
+                    "could not find current directory: {}",
+                    crate::format::io_error(&e)
+                );
+            }
         };
         if let Err(e) = std::env::set_current_dir(&dir) {
-            bail!(cfg, exe, "{}: {}", crate::format::io_error(&e), dir);
+            bail!(
+                cfg,
+                exe,
+                "{}: {}",
+                crate::format::io_error(&e),
+                dir.display()
+            );
         }
+        env.set_prev_pwd(&prev).await;
         async_std::process::ExitStatus::from_raw(0)
     }
 
-- 
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