Make EString::string() join folded ropes, fixing require.resolve() and other readers of the first segment

src/ast/e.rs

@@ -1859,11 +1859,13 @@ impl EString {
     }
 
     pub fn eql_bytes(&self, other: &[u8]) -> bool {
-        if self.is_utf8() {
-            strings::eql_long(&self.data, other, true)
-        } else {
-            strings::utf16_eql_string(self.slice16(), other)
+        if !self.is_utf8() {
+            return strings::utf16_eql_string(self.slice16(), other);
+        }
+        if self.next.is_none() {
+            return strings::eql_long(&self.data, other, true);
         }
+        self.eql8_rope(other)
     }
 
     pub fn eql_comptime(&self, value: &'static [u8]) -> bool {
@@ -1894,44 +1896,53 @@ impl EString {
         true
     }
 
+    /// Copies every segment of a rope into one arena slice.
+    fn join_rope<'b>(&self, bump: &'b Bump) -> &'b [u8] {
+        debug_assert!(self.next.is_some() && self.is_utf8());
+        let mut bytes = bun_alloc::ArenaVec::<u8>::with_capacity_in(self.rope_len as usize, bump);
+        let mut segment: Option<&EString> = Some(self);
+        while let Some(part) = segment {
+            bytes.extend_from_slice(&part.data);
+            segment = part.next.as_deref();
+        }
+        bytes.into_bump_slice()
+    }
+
     pub fn resolve_rope_if_needed(&mut self, bump: &Bump) {
         if self.next.is_none() || !self.is_utf8() {
             return;
         }
-        let mut bytes = bun_alloc::ArenaVec::<u8>::with_capacity_in(self.rope_len as usize, bump);
-        bytes.extend_from_slice(&self.data);
-        let mut str_ = self.next;
-        while let Some(part) = str_ {
-            bytes.extend_from_slice(&part.get().data);
-            str_ = part.get().next;
-        }
-        self.data = Str::new(bytes.into_bump_slice());
+        self.data = Str::new(self.join_rope(bump));
         self.next = None;
     }
 
-    /// Return UTF-8 bytes, transcoding if UTF-16.
-    /// The transcode allocates via the global arena then copies into `bump`.
+    /// Return UTF-8 bytes, transcoding if UTF-16 and joining a rope.
+    /// A rope is joined into `bump` on every call; `slice` stores the joined
+    /// bytes back into the node instead.
     pub fn string<'b>(&self, bump: &'b Bump) -> Result<&'b [u8], AllocError> {
-        if self.is_utf8() {
-            // `self.data` is arena-owned with the same lifetime as `bump`;
-            // StoreStr re-borrows under that contract.
-            Ok(self.data.slice())
-        } else {
+        if !self.is_utf8() {
             let v = strings::to_utf8_alloc(self.slice16());
-            Ok(bump.alloc_slice_copy(&v))
+            return Ok(bump.alloc_slice_copy(&v));
         }
+        if self.next.is_some() {
+            return Ok(self.join_rope(bump));
+        }
+        // `self.data` is arena-owned with the same lifetime as `bump`;
+        // StoreStr re-borrows under that contract.
+        Ok(self.data.slice())
     }
 
     pub(crate) fn string_cloned<'b>(&self, bump: &'b Bump) -> Result<&'b [u8], AllocError> {
-        if self.is_utf8() {
+        if self.is_utf8() && self.next.is_none() {
             Ok(bump.alloc_slice_copy(&self.data))
         } else {
-            let v = strings::to_utf8_alloc(self.slice16());
-            Ok(bump.alloc_slice_copy(&v))
+            // `string` already returns a fresh copy for these.
+            self.string(bump)
         }
     }
 
     pub fn hash(&self) -> u64 {
+        debug_assert!(self.next.is_none(), "hash() on an unresolved rope");
         if self.is_blank() {
             return 0;
         }
@@ -1960,6 +1971,10 @@ impl EString {
     #[inline]
     pub fn order(&self, other: &EString) -> Ordering {
         debug_assert!(self.is_utf8() == other.is_utf8());
+        debug_assert!(
+            self.next.is_none() && other.next.is_none(),
+            "order() on an unresolved rope"
+        );
         if self.is_utf8() {
             strings::order(&self.data, &other.data)
         } else {
@@ -1983,6 +1998,10 @@ impl EString {
 
     // `eql`, split by operand type.
     pub fn eql_string(&self, other: &EString) -> bool {
+        debug_assert!(
+            self.next.is_none() && other.next.is_none(),
+            "eql_string() on an unresolved rope"
+        );
         if self.is_utf8() {
             if other.is_utf8() {
                 strings::eql_long(&self.data, &other.data, true)
@@ -2438,15 +2457,17 @@ impl Import {
         self.import_record_index == u32::MAX
     }
 
-    pub fn import_record_loader(&self) -> Option<crate::Loader> {
+    pub fn import_record_loader(&self, bump: &Bump) -> Option<crate::Loader> {
         let crate::ExprData::EObject(obj) = &self.options.data else {
             return None;
         };
         let with = Object::get(obj, b"with").or_else(|| Object::get(obj, b"assert"))?;
         let crate::ExprData::EObject(with_obj) = &with.data else {
             return None;
         };
-        let str_ = Object::get(with_obj, b"type")?.data.as_e_string()?;
+        let mut str_ = Object::get(with_obj, b"type")?.data.as_e_string()?;
+        // import() options are always constant-folded, so this may be a rope.
+        str_.resolve_rope_if_needed(bump);
 
         if !str_.is_utf16 {
             if let Some(loader) = crate::Loader::from_string(&str_.data) {

src/ast/expr.rs

@@ -2304,12 +2304,15 @@ impl Data {
                 hasher.update(&e.value);
             }
             Data::EString(e) => {
-                // Only the *first* rope segment is hashed.
-                let current: &E::String = e;
-                if current.is_utf8() {
-                    hasher.update(&current.data);
+                if e.is_utf8() {
+                    // Rope segments hash back to back, so "a" + "b" hashes like "ab".
+                    let mut segment: Option<&E::String> = Some(e.get());
+                    while let Some(current) = segment {
+                        hasher.update(&current.data);
+                        segment = current.next.as_deref();
+                    }
                 } else {
-                    hasher.update(bytemuck::cast_slice::<u16, u8>(current.slice16()));
+                    hasher.update(bytemuck::cast_slice::<u16, u8>(e.slice16()));
                 }
                 hasher.update(b"\x00");
             }

src/js_parser/p.rs

@@ -7541,6 +7541,7 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
         str_: &mut E::String,
         loc: bun_ast::Loc,
     ) -> Option<js_ast::ExprData> {
+        str_.resolve_rope_if_needed(self.arena);
         let _ = str_.to_utf8(self.arena);
         let specifier = str_.data;
 

src/js_parser/visit/visit_expr.rs

@@ -1003,6 +1003,7 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
                 let unwrapped = e_.index.unwrap_inlined();
                 if let Some(mut s) = unwrapped.data.e_string() {
                     if !s.is_utf16 {
+                        s.resolve_rope_if_needed(p.arena);
                         // "a['b' + '']" => "a.b"
                         // "enum A { B = 'b' }; a[A.B]" => "a.b"
                         if p.options.features.minify_syntax && s.is_identifier(p.arena) {
@@ -1827,7 +1828,7 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
                     ),
                 import_options: e_.options,
                 loc: e_.expr.loc,
-                import_loader: e_.import_record_loader(),
+                import_loader: e_.import_record_loader(p.arena),
                 ..Default::default()
             };
 
@@ -2380,9 +2381,9 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
         }
 
         // Check if the feature flag is enabled
-        // Use the underlying string data directly without allocation.
         // Feature flag names should be ASCII identifiers, so UTF-16 is unexpected.
-        let flag_string = arg.data.e_string().expect("infallible: variant checked");
+        let mut flag_string = arg.data.e_string().expect("infallible: variant checked");
+        flag_string.resolve_rope_if_needed(p.arena);
         if flag_string.is_utf16 {
             p.log().add_error(
                 Some(p.source),

test/bundler/bun-build-api.test.ts

@@ -71,6 +71,35 @@ describe("Bun.build", () => {
     expect(await bunRun(build.outputs[0].path)).toSpawn("world");
   });
 
+  test("reactFastRefresh signature hashes the whole folded string literal", async () => {
+    // minify.syntax folds "a" + "b" into a rope; the hook signature must cover
+    // every segment, otherwise "a" + "b" and "a" + "c" get the same signature.
+    using dir = tempDir("bun-build-api-refresh-sig", {
+      "ab.tsx": `import { useState } from "react"; export function C() { const [v] = useState("ab"); return <b>{v}</b>; }`,
+      "a-b.tsx": `import { useState } from "react"; export function C() { const [v] = useState("a" + "b"); return <b>{v}</b>; }`,
+      "a-c.tsx": `import { useState } from "react"; export function C() { const [v] = useState("a" + "c"); return <b>{v}</b>; }`,
+    });
+    const signatureOf = async (file: string) => {
+      const build = await Bun.build({
+        entrypoints: [join(String(dir), file)],
+        reactFastRefresh: true,
+        minify: { syntax: true },
+        external: ["react"],
+      });
+      const output = await build.outputs[0].text();
+      const match = output.match(/_s\w*\(C, "([^"]+)"\)/);
+      if (!match) throw new Error(`no refresh signature in ${file}:\n${output}`);
+      return match[1];
+    };
+    const [ab, aPlusB, aPlusC] = await Promise.all([
+      signatureOf("ab.tsx"),
+      signatureOf("a-b.tsx"),
+      signatureOf("a-c.tsx"),
+    ]);
+    expect(aPlusB).toBe(ab);
+    expect(aPlusC).not.toBe(ab);
+  });
+
   test("passing undefined doesnt segfault", () => {
     try {
       // @ts-ignore

test/bundler/bundler_allow_unresolved.test.ts

@@ -226,4 +226,55 @@ describe("bundler", () => {
     backend: "cli",
     allowUnresolved: ["./locales/*.json"],
   });
+
+  // 17-20. Constant folding turns the template head/tail into a rope of string
+  // segments. The shape must include every segment ("./locales/*.json"), not
+  // just the first one ("./loc*.json"), or a matching pattern is rejected.
+  itBundled("allow-unresolved/RopeHeadFromStringAddition", {
+    files: {
+      "/entry.js": /* js */ `
+        export function load(x) {
+          return import("./loc" + \`ales/\${x}.json\`);
+        }
+      `,
+    },
+    outdir: "/out",
+    allowUnresolved: ["./locales/*.json"],
+  });
+
+  itBundled("allow-unresolved/RopeHeadFromTemplateFolding", {
+    files: {
+      "/entry.js": /* js */ `
+        export function load(x) {
+          return import(\`./loc\${"ales"}/\${x}.json\`);
+        }
+      `,
+    },
+    outdir: "/out",
+    allowUnresolved: ["./locales/*.json"],
+  });
+
+  itBundled("allow-unresolved/RopeTailFromStringAddition", {
+    files: {
+      "/entry.js": /* js */ `
+        export function load(x) {
+          return import(\`./locales/\${x}\` + ".json");
+        }
+      `,
+    },
+    outdir: "/out",
+    allowUnresolved: ["./locales/*.json"],
+  });
+
+  itBundled("allow-unresolved/RequireResolveRopeHead", {
+    files: {
+      "/entry.js": /* js */ `
+        export function load(x) {
+          return require.resolve("./loc" + \`ales/\${x}.json\`);
+        }
+      `,
+    },
+    outdir: "/out",
+    allowUnresolved: ["./locales/*.json"],
+  });
 });

test/bundler/bundler_edgecase.test.ts

@@ -2913,6 +2913,36 @@ describe("bundler", () => {
     },
     run: { stdout: "true 1" },
   });
+  // Enum initializers are always constant-folded, so K.X inlines as a rope
+  // ("fo" -> "o"). Without minifySyntax the index visitor used to rewrite the
+  // access with only the first segment: `fo` instead of `foo`.
+  itBundled("edgecase/FoldedEnumStringIndexOnNamespaceImport", {
+    files: {
+      "/entry.ts": /* ts */ `
+        import * as ns from "./ns.ts";
+        enum K { X = "fo" + "o" }
+        console.log(ns[K.X]);
+      `,
+      "/ns.ts": /* ts */ `
+        export const foo = "yes";
+        export const fo = "no";
+      `,
+    },
+    run: { stdout: "yes" },
+  });
+  itBundled("edgecase/FoldedEnumStringIndexAsCommonJSExportName", {
+    files: {
+      "/entry.ts": /* ts */ `
+        import * as k from "./k.ts";
+        console.log(JSON.stringify(Object.keys(k).sort()), k.foo);
+      `,
+      "/k.ts": /* ts */ `
+        enum K { X = "fo" + "o" }
+        exports[K.X] = "value";
+      `,
+    },
+    run: { stdout: '["foo"] value' },
+  });
   // The bundler rewrites bare `require`/`require.main`/`require.resolve` to an
   // ERequireCallTarget / ERequireMain / ERequireResolveCallTarget that prints
   // as `__require` / `__require.main` / `__require.resolve`.

test/bundler/bundler_feature_flag.test.ts

@@ -88,6 +88,28 @@ if (feature("DISABLED_FEATURE")) {
         },
       });
 
+      // minifySyntax folds "ENABLED_" + "FEATURE" before feature() sees it; the
+      // lookup must use the whole folded name, not its first segment.
+      itBundled(`feature_flag/${backend}/FoldedFlagName`, {
+        backend,
+        files: {
+          "/a.js": `
+import { feature } from "bun:bundle";
+if (feature("ENABLED_" + "FEATURE")) {
+  console.log("this should be kept");
+} else {
+  console.log("this should be removed");
+}
+`,
+        },
+        features: ["ENABLED_FEATURE"],
+        minifySyntax: true,
+        onAfterBundle(api) {
+          api.expectFile("out.js").toInclude("this should be kept");
+          api.expectFile("out.js").not.toInclude("this should be removed");
+        },
+      });
+
       itBundled(`feature_flag/${backend}/ImportRemoved`, {
         backend,
         files: {

test/bundler/bundler_loader.test.ts

@@ -151,6 +151,32 @@ describe("bundler", async () => {
     });
   }
 
+  // import() options are visited with constant folding forced on, so these
+  // attribute strings reach the loader lookup as ropes; the lookup must see the
+  // whole string ("json"), not just its first segment ("js" is a real loader).
+  itBundled("bun/loader-dynamic-import-attribute-folded-type", {
+    target: "bun",
+    files: {
+      "/entry.ts": /* js */ `
+        const mod = await import('./hello.notjson', { with: { type: "js" + "on" } });
+        console.write(JSON.stringify(mod.default));
+      `,
+      "/hello.notjson": JSON.stringify({ hello: "world" }),
+    },
+    run: { stdout: '{"hello":"world"}' },
+  });
+  itBundled("bun/loader-dynamic-import-attribute-folded-keys", {
+    target: "bun",
+    files: {
+      "/entry.ts": /* js */ `
+        const mod = await import('./hello.notjson', { ["wi" + "th"]: { ["ty" + "pe"]: "json" } });
+        console.write(JSON.stringify(mod.default));
+      `,
+      "/hello.notjson": JSON.stringify({ hello: "world" }),
+    },
+    run: { stdout: '{"hello":"world"}' },
+  });
+
   itBundled("bun/loader-text-file", {
     target: "bun",
     outfile: "",