wasm-linker: correctly resolve undefined functions

We now resolve undefined symbols during incremental-compilation
where we discard the current symbol if we detect we found
an existing symbol which is not the one currently being updated.
The symbol will always be discarded in favor of the existing symbol
in such a case.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig
index f593f95c3d..60944ff981 100644
--- a/src/link/Wasm.zig
+++ b/src/link/Wasm.zig
@@ -1909,6 +1909,17 @@ pub fn addOrUpdateImport(
         global_gop.value_ptr.* = loc;
         try wasm.resolved_symbols.put(wasm.base.allocator, loc, {});
         try wasm.undefs.putNoClobber(wasm.base.allocator, decl_name_index, loc);
+    } else if (global_gop.value_ptr.*.index != symbol_index) {
+        // We are not updating a symbol, but found an existing global
+        // symbol with the same name. This means we always favor the
+        // existing symbol, regardless whether it's defined or not.
+        // We can also skip storing the import as we will not output
+        // this symbol.
+        return wasm.discarded.put(
+            wasm.base.allocator,
+            .{ .file = null, .index = symbol_index },
+            global_gop.value_ptr.*,
+        );
     }
 
     if (type_index) |ty_index| {
@@ -1924,8 +1935,8 @@ pub fn addOrUpdateImport(
             };
         }
     } else {
+        // non-functions will not be imported from the runtime, but only resolved during link-time
         symbol.tag = .data;
-        return; // non-functions will not be imported from the runtime, but only resolved during link-time
     }
 }