Improve handling of duplicate paths

Currently if we add a duplicate path to a pathlist, it won't get removed
when the changes are unwound. By taking the number of occurrences into
account we can at least remove the duplicate that we added correctly. We
don't have enough info to know which occurence to remove so we always
remove the ones at the front of the pathlist since that's the most
common case.

Author: joshheinrichs-shopify

src/shadowenv.rs

@@ -293,28 +293,27 @@ fn env_prepend_to_pathlist(env: &mut HashMap<String, String>, a: String, b: Stri
 }
 
 fn diff_vecs(oldvec: Vec<&str>, newvec: Vec<&str>) -> (Vec<String>, Vec<String>) {
-    let mut additions: Vec<String> = vec![];
-    let mut deletions: Vec<String> = vec![];
+    let mut delta: BTreeMap<&str, i32> = BTreeMap::new();
 
-    let mut oldset: HashSet<String> = HashSet::new();
-    for oldval in &oldvec {
-        oldset.insert(oldval.to_string());
+    for &item in &oldvec {
+        *delta.entry(item).or_insert(0) -= 1;
     }
-
-    let mut newset: HashSet<String> = HashSet::new();
-    for newval in &newvec {
-        newset.insert(newval.to_string());
+    for &item in &newvec {
+        *delta.entry(item).or_insert(0) += 1;
     }
 
-    for oldval in oldvec {
-        if !newset.contains(oldval) {
-            deletions.push(oldval.to_string());
-        }
-    }
+    let mut additions = Vec::new();
+    let mut deletions = Vec::new();
 
-    for newval in newvec {
-        if !oldset.contains(newval) {
-            additions.push(newval.to_string());
+    for (&item, &count) in &delta {
+        if count > 0 {
+            for _ in 0..count {
+                additions.push(item.to_string());
+            }
+        } else if count < 0 {
+            for _ in 0..(-count) {
+                deletions.push(item.to_string());
+            }
         }
     }
 
@@ -390,13 +389,13 @@ mod tests {
             ],
             lists: vec![List {
                 name: "PATH".to_string(),
-                additions: vec!["/path4".to_string(), "/path3".to_string()],
+                additions: vec!["/path3".to_string(), "/path4".to_string()],
                 deletions: vec!["/path1".to_string()],
             }],
             prev_dirs: Default::default(),
         };
 
-        let expected_formatted_data = r#"00000000075bcd15:{"scalars":[{"name":"VAR_A","original":"v0","current":"v2","no_clobber":false},{"name":"VAR_B","original":"v0","current":null,"no_clobber":false},{"name":"VAR_C","original":null,"current":"v3","no_clobber":false}],"lists":[{"name":"PATH","additions":["/path4","/path3"],"deletions":["/path1"]}],"prev_dirs":[]}"#;
+        let expected_formatted_data = r#"00000000075bcd15:{"scalars":[{"name":"VAR_A","original":"v0","current":"v2","no_clobber":false},{"name":"VAR_B","original":"v0","current":null,"no_clobber":false},{"name":"VAR_C","original":null,"current":"v3","no_clobber":false}],"lists":[{"name":"PATH","additions":["/path3","/path4"],"deletions":["/path1"]}],"prev_dirs":[]}"#;
 
         assert_eq!(shadowenv.shadowenv_data(), expected);