maintain the given order on step execution

Previously step execution disregarded the CLI order and this change executes the given
steps in the order specified on CLI.

For example, running `x $kind a b c` will execute `$kind` step for `a`, then `b`, then `c` crates
in the specified order.

Signed-off-by: onur-ozkan <[email protected]>

Author: onur-ozkan

src/bootstrap/src/core/builder.rs

@@ -473,9 +473,42 @@ impl StepDescription {
             return;
         }
 
-        // Handle all PathSets.
+        let orig_paths = paths.clone();
+
+        // List of `(usize, &StepDescription, Vec<PathSet>)` where `usize` is the closest index of a path
+        // compared to the given CLI paths. So we can respect to the CLI order by using this value to sort
+        // the steps.
+        let mut steps_to_run = vec![];
+
+        let mut indexed_paths: Vec<&PathBuf> = vec![];
+
         for (desc, should_run) in v.iter().zip(&should_runs) {
             let pathsets = should_run.pathset_for_paths_removing_matches(&mut paths, desc.kind);
+
+            // This value is used for sorting the step execution order.
+            // By default, `usize::MAX` is used as the index for steps to assign them the lowest priority.
+            //
+            // If we resolve the step's path from the given CLI input, this value will be updated with
+            // the step's actual index.
+            let mut closest_index = usize::MAX;
+
+            // Find the closest index from the original list of paths given by the CLI input.
+            for (index, value) in orig_paths.iter().enumerate() {
+                if !indexed_paths.contains(&value) && !paths.contains(value) {
+                    closest_index = index;
+                    indexed_paths.push(value);
+                    break;
+                }
+            }
+
+            steps_to_run.push((closest_index, desc, pathsets));
+        }
+
+        // Sort the steps before running them to respect the CLI order.
+        steps_to_run.sort_by_key(|(index, _, _)| *index);
+
+        // Handle all PathSets.
+        for (_index, desc, pathsets) in steps_to_run {
             if !pathsets.is_empty() {
                 desc.maybe_run(builder, pathsets);
             }