From a66692761fa2db26acbfc7d48a67cbaa9159a9f9 Mon Sep 17 00:00:00 2001
From: Claude Bot <claude-bot@bun.sh>
Date: Wed, 23 Jul 2025 21:58:31 +0000
Subject: [PATCH] Fix duplicate exports when entry points re-export from other
 entry points (#5344)
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When code splitting is enabled and one entry point re-exports from another
entry point, the bundler was generating duplicate export statements. This
happened because both the cross-chunk export generation logic and the entry
point export generation logic were creating export statements for the same
symbols.

The fix prevents cross-chunk export statement generation for entry points
that have their own sorted export aliases, since these entry points will
generate their own exports in generateEntryPointTailJS().

Test cases added to verify:
- Basic re-export scenario between two entry points
- Multiple re-exports through intermediate modules

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 .../computeCrossChunkDependencies.zig         |  8 ++-
 test/bundler/bundler_regressions.test.ts      | 61 +++++++++++++++++++
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/src/bundler/linker_context/computeCrossChunkDependencies.zig b/src/bundler/linker_context/computeCrossChunkDependencies.zig
index 25e2b5bcf7..465283b6d2 100644
--- a/src/bundler/linker_context/computeCrossChunkDependencies.zig
+++ b/src/bundler/linker_context/computeCrossChunkDependencies.zig
@@ -334,7 +334,13 @@ fn computeCrossChunkDependenciesWithChunkMetas(c: *LinkerContext, chunks: []Chun
                         );
                     }
 
-                    if (clause_items.len > 0) {
+                    // Only generate cross-chunk export statements if there are items to export
+                    // and if this chunk is not an entry point with sorted export aliases
+                    // (which indicates it will generate its own exports in generateEntryPointTailJS)
+                    const sorted_and_filtered_export_aliases = c.graph.meta.items(.sorted_and_filtered_export_aliases)[chunk.entry_point.source_index];
+                    const should_skip_cross_chunk_exports = chunk.entry_point.is_entry_point and sorted_and_filtered_export_aliases.len > 0;
+                    
+                    if (clause_items.len > 0 and !should_skip_cross_chunk_exports) {
                         var stmts = BabyList(js_ast.Stmt).initCapacity(c.allocator, 1) catch unreachable;
                         const export_clause = c.allocator.create(js_ast.S.ExportClause) catch unreachable;
                         export_clause.* = .{
diff --git a/test/bundler/bundler_regressions.test.ts b/test/bundler/bundler_regressions.test.ts
index e4efcf36f8..98514be815 100644
--- a/test/bundler/bundler_regressions.test.ts
+++ b/test/bundler/bundler_regressions.test.ts
@@ -294,4 +294,65 @@ describe("bundler", () => {
     run: true,
     capture: ["1 /* Value */", "1 /* Value */", "1 /* Value */"],
   });
+
+  // https://github.com/oven-sh/bun/issues/5344
+  itBundled("regression/DuplicateExports#5344", {
+    files: {
+      "/entry-b.ts": `
+        export function b() {}
+      `,
+      "/entry-a.ts": `
+        export { b } from "./entry-b.ts";
+        export function a() {}
+      `,
+    },
+    entryPoints: ["/entry-a.ts", "/entry-b.ts"],
+    outdir: "/out",
+    format: "esm",
+    splitting: true,
+    onAfterBundle(api) {
+      // Check entry-b.js output for duplicate exports
+      const entryB = api.readFile("/out/entry-b.js");
+      
+      // Count all export statements (both single line and multiline)
+      const exportMatches = entryB.match(/export\s*\{[^}]*\}/g);
+      
+      if (exportMatches && exportMatches.length > 1) {
+        throw new Error(`Found ${exportMatches.length} export statements (expected 1) in entry-b.js:\n${exportMatches.join('\n')}\n\nFull output:\n${entryB}`);
+      }
+    },
+  });
+
+  // Additional test case for multiple re-exports
+  itBundled("regression/DuplicateExports#5344-MultipleReExports", {
+    files: {
+      "/lib.ts": `
+        export const value = 42;
+        export function helper() { return "helper"; }
+      `,
+      "/intermediate.ts": `
+        export { value, helper } from "./lib.ts";
+      `,
+      "/entry.ts": `
+        export { value, helper } from "./intermediate.ts";
+        export const main = "main";
+      `,
+    },
+    entryPoints: ["/entry.ts", "/intermediate.ts", "/lib.ts"],
+    outdir: "/out",
+    format: "esm",
+    splitting: true,
+    onAfterBundle(api) {
+      // Check each file for duplicate exports
+      const files = ["entry.js", "intermediate.js", "lib.js"];
+      for (const file of files) {
+        const content = api.readFile(`/out/${file}`);
+        const exportMatches = content.match(/export\s*\{[^}]*\}/g);
+        
+        if (exportMatches && exportMatches.length > 1) {
+          throw new Error(`Found ${exportMatches.length} export statements (expected max 1) in ${file}:\n${exportMatches.join('\n')}\n\nFull output:\n${content}`);
+        }
+      }
+    },
+  });
 });