Ely Office: six offline-first desktop apps in Rust and GPUI

ElyDoc, ElyTable, ElyShow (LibreOfficeKit), ElyPDF (MuPDF), ElyTree (Git),
ElyMark (Milkdown and CodeMirror in CEF). ElyMail and ElyAgent follow.

crates/ely-platform/src/env.rs

@@ -0,0 +1,36 @@
+/// An environment variable's text; none when unset.
+pub fn value(name: &str) -> Option<String> {
+    std::env::var_os(name).map(|value| value.to_string_lossy().into_owned())
+}
+
+/// A 0 or 1 switch; anything else warns.
+pub fn flag(name: &str) -> Option<bool> {
+    flag_from(name, value(name).as_deref())
+}
+
+fn flag_from(name: &str, value: Option<&str>) -> Option<bool> {
+    match value {
+        None => None,
+        Some("1") => Some(true),
+        Some("0") => Some(false),
+        Some(other) => {
+            log::warn!("env: {name}={other} is not 0 or 1, ignored");
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::flag_from;
+
+    #[test]
+    fn only_zero_and_one_are_answers() {
+        assert_eq!(flag_from("X", Some("1")), Some(true));
+        assert_eq!(flag_from("X", Some("0")), Some(false));
+        assert_eq!(flag_from("X", None), None);
+        for other in ["", "true", "false", "off", "yes", " 1", "01"] {
+            assert_eq!(flag_from("X", Some(other)), None, "{other:?}");
+        }
+    }
+}