Add changes subcommand

For some tooling (e.g. editors, prompts) it's helpful to know what
modifications Shadowenv has made, in a short summary. This PR adds a
`changes` subcommand that does just that: prints out a summary of
the form `+added -removed ^updated`.

Author: Rami Chowdhury

src/changes.rs

@@ -0,0 +1,105 @@
+use std::fmt;
+
+use failure::{Error, Fail};
+
+use crate::undo;
+
+#[derive(Fail, Debug)]
+#[fail(display = "Could not output changes")]
+pub struct ChangesError;
+
+#[derive(PartialEq, Eq, Debug)]
+pub struct Changes {
+    added: usize,
+    removed: usize,
+    updated: usize,
+}
+
+impl fmt::Display for Changes {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "+{added} -{removed} ^{updated}",
+            added = self.added,
+            removed = self.removed,
+            updated = self.updated
+        )
+    }
+}
+
+#[derive(Debug)]
+enum ChangeType {
+    Added,
+    Removed,
+    Updated,
+    Unchanged,
+}
+
+/// How has this environment variable changed?
+fn change_type(v: &undo::Scalar) -> ChangeType {
+    match (v.original.as_ref(), v.current.as_ref()) {
+        (None, None) => ChangeType::Unchanged,
+        (None, Some(_)) => ChangeType::Added,
+        (Some(_), None) => ChangeType::Removed,
+        (Some(a), Some(b)) if a == b => ChangeType::Unchanged,
+        (Some(a), Some(b)) if a == "" && b != "" => ChangeType::Added,
+        (Some(a), Some(b)) if a != "" && b == "" => ChangeType::Removed,
+        (Some(a), Some(b)) if a != b => ChangeType::Updated,
+        (Some(_), Some(_)) => ChangeType::Updated,
+    }
+}
+
+/// Output a simple summary of the changes
+pub fn run(shadowenv_data: String) -> Result<Changes, Error> {
+    let mut parts = shadowenv_data.splitn(2, ':');
+    let _prev_hash = parts.next();
+    let json_data = parts.next().unwrap_or("{}");
+    let shadowenv_data = undo::Data::from_str(json_data).unwrap();
+    let mut changes = Changes {
+        added: 0,
+        removed: 0,
+        updated: 0,
+    };
+    for s in shadowenv_data.scalars {
+        match change_type(&s) {
+            ChangeType::Added => changes.added += 1,
+            ChangeType::Updated => changes.updated += 1,
+            ChangeType::Removed => changes.removed += 1,
+            ChangeType::Unchanged => {}
+        }
+    }
+    for l in shadowenv_data.lists {
+        if l.additions.len() != 0 || l.deletions.len() != 0 {
+            changes.updated += 1;
+        }
+    }
+    Ok(changes)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn display_test() {
+        let changes = Changes {
+            added: 1,
+            updated: 2,
+            removed: 3,
+        };
+        assert_eq!(changes.to_string(), "+1 -3 ^2",);
+    }
+
+    #[test]
+    fn nominal_test() {
+        let data = r#"d6508595be775af2:{"scalars":[{"name":"CLICOLOR","original":"1","current":"0"},{"name":"DEBUG","original":null,"current":"1"},{"name":"GOPATH","original":"/Users/rami/Go","current":""},{"name":"INFOPATH","original":"/opt/homebrew/share/info:","current":""},{"name":"NODE_PATH","original":"/Users/rami/.npm/packages/lib/node_modules:","current":""}],"lists":[{"name":"PATH","additions":["/usr/libexec/bin"],"deletions":[]}]}"#;
+        let result = run(data.to_string());
+
+        let expected: Changes = Changes {
+            added: 1,
+            updated: 2,
+            removed: 3,
+        };
+        assert_eq!(result.unwrap(), expected);
+    }
+}

src/cli.rs

@@ -148,4 +148,9 @@ pub fn app() -> App<'static, 'static> {
                         .about("Prints a script which can be eval'd by fish to set up shadowenv."),
                 )
         )
+        .subcommand(
+            SubCommand::with_name("change-count")
+                .about("Show the number of variables set / updated. Useful for tooling e.g. IDEs, prompts.")
+                .setting(AppSettings::DisableHelpSubcommand)
+        )
 }

src/main.rs

@@ -1,3 +1,4 @@
+mod changes;
 mod cli;
 mod diff;
 mod execcmd;
@@ -83,6 +84,19 @@ fn main() {
             let shellname = matches.subcommand_name().unwrap();
             process::exit(init::run(shellname));
         }
+        ("changes", Some(matches)) => {
+            let legacy_fallback_data = matches.value_of("$__shadowenv_data").map(|d| d.to_string());
+            let data = Shadowenv::load_shadowenv_data_or_legacy_fallback(legacy_fallback_data);
+            match changes::run(data) {
+                Err(err) => {
+                    eprintln!("{}", err);
+                    process::exit(1);
+                }
+                Ok(changes) => {
+                    print!("{}", changes);
+                }
+            }
+        }
         _ => {
             panic!("subcommand was required by config but somehow none was provided");
         }