transpile: deduplicate imports from main module itself vs. submodules

Author: fw-immunant

c2rust-transpile/src/rust_ast/item_store.rs

@@ -78,6 +78,24 @@ impl PathedMultiImports {
             })
             .collect()
     }
+
+    /// Remove all imports covered by the other `PathedMultiImports`.
+    pub fn remove(&mut self, other: &PathedMultiImports) {
+        for (k, v) in &mut self.0 {
+            // We don't consider attributes, just subtract leaf sets.
+            let other_items = other
+                .0
+                .get(k)
+                .map(|imports| {
+                    imports
+                        .leaves
+                        .iter()
+                        .collect::<std::collections::HashSet<_>>()
+                })
+                .unwrap_or_default();
+            v.leaves.retain(|leaf| !other_items.contains(leaf));
+        }
+    }
 }
 
 #[derive(Debug, Default)]

c2rust-transpile/src/translator/mod.rs

@@ -879,14 +879,17 @@ pub fn translate(
 
             all_items.extend(mod_items);
 
+            // Before consuming `uses`, remove them from the uses from submodules to avoid duplicates.
+            let (_, _, mut new_uses) = new_uses.drain();
+            new_uses.remove(&uses);
+
             // This could have been merged in with items below; however, it's more idiomatic to have
             // imports near the top of the file than randomly scattered about. Also, there is probably
             // no reason to have comments associated with imports so it doesn't need to go through
             // the above comment store process
             all_items.extend(uses.into_items());
 
             // Print new uses from submodules
-            let (_, _, new_uses) = new_uses.drain();
             all_items.extend(new_uses.into_items());
 
             if !foreign_items.is_empty() {