Use sequoia-directories.

- Use `sequoia-directories` to compute the home directory, and the
    various component directories.

  - This also allows the use of `SEQUOIA_HOME` to set the home
    directory.

Cargo.lock

@@ -3413,6 +3413,7 @@ dependencies = [
  "rpassword",
  "sequoia-autocrypt",
  "sequoia-cert-store",
+ "sequoia-directories",
  "sequoia-keystore",
  "sequoia-net",
  "sequoia-openpgp",

Cargo.toml

@@ -32,6 +32,7 @@ maintenance = { status = "actively-developed" }
 buffered-reader = { version = "1.3.1", default-features = false, features = ["compression"] }
 dirs = "5"
 dot-writer = { version = "0.1.3", optional = true }
+sequoia-directories = "0.1"
 sequoia-openpgp = { version = "1.18", default-features = false, features = ["compression"] }
 sequoia-autocrypt = { version = "0.25", default-features = false }
 sequoia-net = { version = "0.28", default-features = false }
@@ -62,8 +63,10 @@ buffered-reader = { version = "1.0.0", default-features = false, features = ["co
 clap = { version = "4", features = ["derive", "env", "string", "wrap_help"] }
 clap_complete = "4"
 chrono = "0.4.10"
+dirs = "5"
 roff = "0.2.1"
 serde = { version = "1.0.137", features = ["derive"] }
+sequoia-directories = "0.1"
 sequoia-openpgp = { version = "1.17", default-features = false }
 sequoia-net = { version = "0.28", default-features = false }
 subplot-build = { version = ">=0.7, <0.10", optional = true }

src/cli/mod.rs

@@ -209,6 +209,35 @@ pub struct SqCommand {
         help = "Overwrite existing files",
     )]
     pub force: bool,
+    #[clap(
+        long,
+        env = "SEQUOIA_HOME",
+        global = true,
+        help_heading = GLOBAL_OPTIONS_HEADER,
+        help = "Set the home directory.",
+        long_help = format!("\
+Set the home directory.
+
+Sequoia's default home directory is `{}`.  When using the default \
+location, files are placed according to the local standard, \
+e.g., the XDG Base Directory Specification.  When an alternate \
+location is specified, the user data, configuration files, and \
+cache data are placed under a single, unified directory.  This is \
+a lightweight way to partially isolate `sq`.",
+            sequoia_directories::Home::default_location()
+                .map(|p| {
+                    let p = p.display().to_string();
+                    if let Some(home) = dirs::home_dir() {
+                        let home = home.display().to_string();
+                        if let Some(rest) = p.strip_prefix(&home) {
+                            return format!("$HOME{}", rest);
+                        }
+                    }
+                    p
+                })
+                .unwrap_or("<unknown>".to_string())),
+    )]
+    pub home: Option<PathBuf>,
     #[clap(
         long,
         global = true,
@@ -229,15 +258,28 @@ key store."
         global = true,
         help_heading = GLOBAL_OPTIONS_HEADER,
         help = "Override the key store server and its data",
-        long_help = "\
-A key store server manages and protects secret key material.  By
-default, `sq` connects to the key store server listening on
-`$XDG_DATA_HOME/sequoia/keystore`.  If no key store server is running,
+        long_help = format!("\
+A key store server manages and protects secret key material.  By \
+default, `sq` connects to the key store server for Sequoia's default \
+home directory (see `--home`), {}.  If no key store server is running, \
 one is started.
 
-This option causes `sq` to use an alternate key store server.  If
-necessary, a key store server is started, and configured to look for
-its data in the specified location."
+This option causes `sq` to use an alternate key store server.  If \
+necessary, a key store server is started, and configured to look for \
+its data in the specified location.",
+            sequoia_directories::Home::default()
+                .map(|home| {
+                    let p = home.data_dir(sequoia_directories::Component::Keystore);
+                    let p = p.display().to_string();
+                    if let Some(home) = dirs::home_dir() {
+                        let home = home.display().to_string();
+                        if let Some(rest) = p.strip_prefix(&home) {
+                            return format!("$HOME{}", rest);
+                        }
+                    }
+                    p
+                })
+                .unwrap_or("<unknown>".to_string())),
     )]
     pub key_store: Option<PathBuf>,
     #[clap(
@@ -258,10 +300,25 @@ standard cert-d, which is located in `$HOME/.local/share/pgp.cert.d`."
         global = true,
         help_heading = GLOBAL_OPTIONS_HEADER,
         help = "Specify the location of the certificate store",
-        long_help = "\
-Specify the location of the certificate store.  By default, sq uses \
-the OpenPGP certificate directory at `$HOME/.local/share/pgp.cert.d`, \
-and creates it if it does not exist."
+        long_help = format!("\
+Specify the location of the certificate store.  By default, `sq` uses \
+the OpenPGP certificate directory in Sequoia's home directory (see `--home`), \
+{}.  This can be overridden by setting the `PGP_CERT_D` environment \
+variable.  That in turn can be overridden by setting the `SQ_CERT_STORE` \
+environment variable.",
+            sequoia_directories::Home::default()
+                .map(|home| {
+                    let p = home.data_dir(sequoia_directories::Component::CertD);
+                    let p = p.display().to_string();
+                    if let Some(home) = dirs::home_dir() {
+                        let home = home.display().to_string();
+                        if let Some(rest) = p.strip_prefix(&home) {
+                            return format!("$HOME{}", rest);
+                        }
+                    }
+                    p
+                })
+                .unwrap_or("<unknown>".to_string())),
     )]
     pub cert_store: Option<PathBuf>,
     #[clap(

src/sq.rs

@@ -416,6 +416,7 @@ pub struct Config<'store, 'rstore>
     output_version: Option<OutputVersion>,
     policy: &'rstore P<'rstore>,
     time: SystemTime,
+    home: sequoia_directories::Home,
     // --no-cert-store
     no_rw_cert_store: bool,
     cert_store_path: Option<PathBuf>,
@@ -468,14 +469,10 @@ impl<'store: 'rstore, 'rstore> Config<'store, 'rstore> {
             None
         } else if let Some(path) = self.cert_store_path.as_ref() {
             Some(path.clone())
+        } else if let Ok(path) = std::env::var("PGP_CERT_D") {
+            Some(PathBuf::from(path))
         } else {
-            // XXX: openpgp-cert-d doesn't yet export this:
-            // https://gitlab.com/sequoia-pgp/pgp-cert-d/-/issues/34
-            // Remove this when it does.
-            let pathbuf = dirs::data_dir()
-                .expect("Unsupported platform")
-                .join("pgp.cert.d");
-            Some(pathbuf)
+            Some(self.home.data_dir(sequoia_directories::Component::CertD))
         }
     }
 
@@ -694,11 +691,9 @@ impl<'store: 'rstore, 'rstore> Config<'store, 'rstore> {
             Ok(None)
         } else if let Some(dir) = self.key_store_path.as_ref() {
             Ok(Some(dir.clone()))
-        } else if let Some(dir) = dirs::data_dir() {
-            Ok(Some(dir.join("sequoia/keystore")))
         } else {
-            Err(anyhow::anyhow!(
-                "No key store, the XDG data directory is not defined"))
+            let home = sequoia_directories::Home::new(None)?;
+            Ok(Some(home.data_dir(sequoia_directories::Component::Keystore)))
         }
     }
 
@@ -1330,6 +1325,7 @@ fn main() -> Result<()> {
         output_version,
         policy: &policy,
         time,
+        home: sequoia_directories::Home::new(c.home.clone())?,
         no_rw_cert_store: c.no_cert_store,
         cert_store_path: c.cert_store.clone(),
         pep_cert_store_path: c.pep_cert_store.clone(),