1 files changed, 119 insertions, 0 deletions
diff --git a/library/std/src/sys_common/process.rs b/library/std/src/sys_common/process.rs
new file mode 100644
index 000000000..9f978789a
--- /dev/null
+++ b/library/std/src/sys_common/process.rs
@@ -0,0 +1,119 @@
+#![allow(dead_code)]
+#![unstable(feature = "process_internals", issue = "none")]
+
+use crate::collections::BTreeMap;
+use crate::env;
+use crate::ffi::{OsStr, OsString};
+use crate::sys::process::EnvKey;
+
+// Stores a set of changes to an environment
+#[derive(Clone, Debug)]
+pub struct CommandEnv {
+    clear: bool,
+    saw_path: bool,
+    vars: BTreeMap<EnvKey, Option<OsString>>,
+}
+
+impl Default for CommandEnv {
+    fn default() -> Self {
+        CommandEnv { clear: false, saw_path: false, vars: Default::default() }
+    }
+}
+
+impl CommandEnv {
+    // Capture the current environment with these changes applied
+    pub fn capture(&self) -> BTreeMap<EnvKey, OsString> {
+        let mut result = BTreeMap::<EnvKey, OsString>::new();
+        if !self.clear {
+            for (k, v) in env::vars_os() {
+                result.insert(k.into(), v);
+            }
+        }
+        for (k, maybe_v) in &self.vars {
+            if let &Some(ref v) = maybe_v {
+                result.insert(k.clone(), v.clone());
+            } else {
+                result.remove(k);
+            }
+        }
+        result
+    }
+
+    pub fn is_unchanged(&self) -> bool {
+        !self.clear && self.vars.is_empty()
+    }
+
+    pub fn capture_if_changed(&self) -> Option<BTreeMap<EnvKey, OsString>> {
+        if self.is_unchanged() { None } else { Some(self.capture()) }
+    }
+
+    // The following functions build up changes
+    pub fn set(&mut self, key: &OsStr, value: &OsStr) {
+        let key = EnvKey::from(key);
+        self.maybe_saw_path(&key);
+        self.vars.insert(key, Some(value.to_owned()));
+    }
+
+    pub fn remove(&mut self, key: &OsStr) {
+        let key = EnvKey::from(key);
+        self.maybe_saw_path(&key);
+        if self.clear {
+            self.vars.remove(&key);
+        } else {
+            self.vars.insert(key, None);
+        }
+    }
+
+    pub fn clear(&mut self) {
+        self.clear = true;
+        self.vars.clear();
+    }
+
+    pub fn have_changed_path(&self) -> bool {
+        self.saw_path || self.clear
+    }
+
+    fn maybe_saw_path(&mut self, key: &EnvKey) {
+        if !self.saw_path && key == "PATH" {
+            self.saw_path = true;
+        }
+    }
+
+    pub fn iter(&self) -> CommandEnvs<'_> {
+        let iter = self.vars.iter();
+        CommandEnvs { iter }
+    }
+}
+
+/// An iterator over the command environment variables.
+///
+/// This struct is created by
+/// [`Command::get_envs`][crate::process::Command::get_envs]. See its
+/// documentation for more.
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+#[stable(feature = "command_access", since = "1.57.0")]
+#[derive(Debug)]
+pub struct CommandEnvs<'a> {
+    iter: crate::collections::btree_map::Iter<'a, EnvKey, Option<OsString>>,
+}
+
+#[stable(feature = "command_access", since = "1.57.0")]
+impl<'a> Iterator for CommandEnvs<'a> {
+    type Item = (&'a OsStr, Option<&'a OsStr>);
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next().map(|(key, value)| (key.as_ref(), value.as_deref()))
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[stable(feature = "command_access", since = "1.57.0")]
+impl<'a> ExactSizeIterator for CommandEnvs<'a> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}