1 files changed, 9 insertions, 2 deletions
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 03059cd6d64..d7f6fa347be 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -454,15 +454,22 @@ impl Options {
             return None;
         }
 
-        let mut emit = Vec::new();
+        let mut emit = FxIndexMap::<_, EmitType>::default();
         for list in matches.opt_strs("emit") {
             for kind in list.split(',') {
                 match kind.parse() {
-                    Ok(kind) => emit.push(kind),
+                    Ok(kind) => {
+                        // De-duplicate emit types and the last wins.
+                        // Only one instance for each type is allowed
+                        // regardless the actual data it carries.
+                        // This matches rustc's `--emit` behavior.
+                        emit.insert(std::mem::discriminant(&kind), kind);
+                    }
                     Err(()) => dcx.fatal(format!("unrecognized emission type: {kind}")),
                 }
             }
         }
+        let emit = emit.into_values().collect::<Vec<_>>();
 
         let show_coverage = matches.opt_present("show-coverage");
         let output_format_s = matches.opt_str("output-format");