From 91d8b7b8dc04aecea1a4fa7c6c6bc0696ebdada4 Mon Sep 17 00:00:00 2001
From: Matthew Lugg <mlugg@mlugg.co.uk>
Date: Mon, 31 Aug 2026 05:42:43 -0400
Subject: [PATCH] Zcu: notify the linker once source files have been scanned

---
 src/Zcu/PerThread.zig |  2 ++
 src/link.zig          | 48 +++++++++++++++++++++++++++++++------------
 src/link/Elf2.zig     |  4 ++++
 3 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/src/Zcu/PerThread.zig b/src/Zcu/PerThread.zig
index 0e4962985a566aa611a326ea1aeb2b61e9928ae4..9a34d3ebdbf7be956d066caf98a71933afabf137 100644
--- a/src/Zcu/PerThread.zig
+++ b/src/Zcu/PerThread.zig
@@ -258,6 +258,8 @@ pub fn update(
         return;
     }
 
+    try comp.link_queue.enqueueZcu(comp, pt.tid, .files_ready);
+
     if (comp.config.incremental) {
         const update_zir_refs_node = main_progress_node.start("Update ZIR References", 0);
         defer update_zir_refs_node.end();
diff --git a/src/link.zig b/src/link.zig
index d5c0759bfc353ca7982f3aa94546b7ae431975b1..d084cd7e41f53cdf4854b556b545c985ecf812bd 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -794,6 +794,28 @@ pub const File = struct {
         }
     }
 
+    /// When there is a ZCU, this is called exactly once per update, to indicate that all per-file
+    /// state (e.g. `Zcu.alive_files`) has been populated by the frontend, so can now be safely
+    /// accessed by the linker.
+    ///
+    /// This call occurs before any call to any of these functions:
+    /// * `updateNav`
+    /// * `updateFunc`
+    /// * `updateContainerType`
+    /// * `updateLineNumber`
+    ///
+    /// Asserts that the ZCU is not using the LLVM backend.
+    fn zcuFilesReady(base: *File) Error!void {
+        assert(base.comp.zcu.?.llvm_object == null);
+        switch (base.tag) {
+            else => {},
+            inline .elf2 => |tag| {
+                dev.check(tag.devFeature());
+                return @as(*tag.Type(), @fieldParentPtr("base", base)).zcuFilesReady();
+            },
+        }
+    }
+
     /// Asserts that the ZCU is not using the LLVM backend.
     fn updateNav(base: *File, pt: Zcu.PerThread, nav_index: InternPool.Nav.Index) Error!void {
         assert(base.comp.zcu.?.llvm_object == null);
@@ -823,19 +845,6 @@ pub const File = struct {
         }
     }
 
-    /// Never called when LLVM is codegenning the ZCU.
-    fn clearContainerType(base: *File, pt: Zcu.PerThread, ty: InternPool.Index) Error!void {
-        assert(base.comp.zcu.?.llvm_object == null);
-        switch (base.tag) {
-            .lld => unreachable,
-            else => {},
-            inline .elf => |tag| {
-                dev.check(tag.devFeature());
-                return @as(*tag.Type(), @fieldParentPtr("base", base)).clearContainerType(pt, ty);
-            },
-        }
-    }
-
     /// The active tag of `mir` is determined by the backend used for the module this function is in.
     /// Never called when LLVM is codegenning the ZCU.
     fn updateFunc(
@@ -1417,6 +1426,9 @@ pub const PrelinkTask = union(enum) {
     load_dso: Path,
 };
 pub const ZcuTask = union(enum) {
+    /// Sent once per update, as the very first `ZcuTask` in the update. Indicates that all per-file
+    /// state (e.g. `Zcu.alive_files`) is populated so can now be safely accessed by the linker.
+    files_ready,
     /// Write the constant value for a Decl to the output file.
     link_nav: InternPool.Nav.Index,
     /// Write the machine code for a function to the output file.
@@ -1620,6 +1632,16 @@ pub fn doZcuTask(comp: *Compilation, tid: Zcu.PerThread.Id, task: ZcuTask) void
     var timer = comp.startTimer();
 
     const maybe_nav: ?InternPool.Nav.Index = switch (task) {
+        .files_ready => {
+            if (zcu.llvm_object != null) return;
+            const lf = comp.bin_file orelse return;
+            lf.zcuFilesReady() catch |err| switch (err) {
+                error.Canceled => io.recancel(),
+                error.AlreadyReported => return,
+                error.OutOfMemory => return diags.setAllocFailure(),
+            };
+            return;
+        },
         .link_nav => |nav_index| nav: {
             const fqn_slice = ip.getNav(nav_index).fqn.toSlice(ip);
             const nav_prog_node = comp.link_prog_node.start(fqn_slice, 0);
diff --git a/src/link/Elf2.zig b/src/link/Elf2.zig
index 4c5071fad3768f6123121295d5eeacd2c5b5443a..5dfb87ceb014d82837c13d1910612d6f059a06f7 100644
--- a/src/link/Elf2.zig
+++ b/src/link/Elf2.zig
@@ -7148,6 +7148,10 @@ fn prelinkInner(elf: *Elf) Error!void {
     }
 }
 
+pub fn zcuFilesReady(elf: *Elf) link.Error!void {
+    _ = elf; // TODO jacobly
+}
+
 fn prepareDynamic(elf: *Elf) Error!void {
     const comp = elf.base.comp;
 
-- 
2.54.0