frontend: fix reference tracking through coerced function bodies

This bug was manifesting for user as a nasty link error because they
were calling their application's main entry point as a coerced function,
which essentially broke reference tracking for the entire ZCU, causing
exported symbols to silently not get exported.

I've been a little unsure about how coerced functions should interact
with the unit graph before, but the solution is actually really obvious
now: they shouldn't! `Sema` is now responsible for unwrapping
possibly-coerced functions *before* queuing analysis or marking unit
references. This makes the reference graph optimal (there are no
redundant edges representing coerced versions of the same function) and
simplifies logic elsewhere at the expense of just a few lines in Sema.

1 files changed, 37 insertions, 19 deletions

diff --git a/src/Sema.zig b/src/Sema.zig
index 51b93fb308..385e1ae74a 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -4376,8 +4376,9 @@ fn zirResolveInferredAlloc(sema: *Sema, block: *Block, inst: Zir.Inst.Index) Com
             if (zcu.intern_pool.isFuncBody(val)) {
                 const ty: Type = .fromInterned(zcu.intern_pool.typeOf(val));
                 if (try ty.fnHasRuntimeBitsSema(pt)) {
-                    try sema.addReferenceEntry(block, src, AnalUnit.wrap(.{ .func = val }));
-                    try zcu.ensureFuncBodyAnalysisQueued(val);
+                    const orig_fn_index = zcu.intern_pool.unwrapCoercedFunc(val);
+                    try sema.addReferenceEntry(block, src, .wrap(.{ .func = orig_fn_index }));
+                    try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
                 }
             }
 
@@ -5589,16 +5590,21 @@ fn zirPanic(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void
     }
 
     try sema.ensureMemoizedStateResolved(src, .panic);
-    try zcu.ensureFuncBodyAnalysisQueued(zcu.builtin_decl_values.get(.@"panic.call"));
-
-    const panic_fn = Air.internedToRef(zcu.builtin_decl_values.get(.@"panic.call"));
-
+    const panic_fn_index = zcu.builtin_decl_values.get(.@"panic.call");
     const opt_usize_ty = try pt.optionalType(.usize_type);
     const null_ret_addr = Air.internedToRef((try pt.intern(.{ .opt = .{
         .ty = opt_usize_ty.toIntern(),
         .val = .none,
     } })));
-    try sema.callBuiltin(block, src, panic_fn, .auto, &.{ coerced_msg, null_ret_addr }, .@"@panic");
+    // `callBuiltin` also calls `addReferenceEntry` to the function body for us.
+    try sema.callBuiltin(
+        block,
+        src,
+        .fromIntern(panic_fn_index),
+        .auto,
+        &.{ coerced_msg, null_ret_addr },
+        .@"@panic",
+    );
 }
 
 fn zirTrap(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
@@ -7567,8 +7573,9 @@ fn analyzeCall(
         ref_func: {
             const runtime_func_val = try sema.resolveValue(runtime_func) orelse break :ref_func;
             if (!ip.isFuncBody(runtime_func_val.toIntern())) break :ref_func;
-            try sema.addReferenceEntry(block, call_src, .wrap(.{ .func = runtime_func_val.toIntern() }));
-            try zcu.ensureFuncBodyAnalysisQueued(runtime_func_val.toIntern());
+            const orig_fn_index = ip.unwrapCoercedFunc(runtime_func_val.toIntern());
+            try sema.addReferenceEntry(block, call_src, .wrap(.{ .func = orig_fn_index }));
+            try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
         }
 
         const call_tag: Air.Inst.Tag = switch (modifier) {
@@ -26383,23 +26390,27 @@ fn explainWhyTypeIsNotPacked(
 /// instructions. This function ensures the panic function will be available to
 /// be called during that time.
 fn preparePanicId(sema: *Sema, src: LazySrcLoc, panic_id: Zcu.SimplePanicId) !void {
+    const zcu = sema.pt.zcu;
+
     // If the backend doesn't support `.panic_fn`, it doesn't want us to lower the panic handlers.
     // The backend will transform panics into traps instead.
-    if (sema.pt.zcu.backendSupportsFeature(.panic_fn)) {
-        _ = try sema.getPanicIdFunc(src, panic_id);
-    }
+    if (!zcu.backendSupportsFeature(.panic_fn)) return;
+
+    const fn_index = try sema.getPanicIdFunc(src, panic_id);
+    const orig_fn_index = zcu.intern_pool.unwrapCoercedFunc(fn_index);
+    try sema.addReferenceEntry(null, src, .wrap(.{ .func = orig_fn_index }));
+    try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
 }
 
 fn getPanicIdFunc(sema: *Sema, src: LazySrcLoc, panic_id: Zcu.SimplePanicId) !InternPool.Index {
     const zcu = sema.pt.zcu;
     try sema.ensureMemoizedStateResolved(src, .panic);
-    const panic_func = zcu.builtin_decl_values.get(panic_id.toBuiltin());
-    try zcu.ensureFuncBodyAnalysisQueued(panic_func);
+    const panic_fn_index = zcu.builtin_decl_values.get(panic_id.toBuiltin());
     switch (sema.owner.unwrap()) {
         .@"comptime", .nav_ty, .nav_val, .type, .memoized_state => {},
         .func => |owner_func| zcu.intern_pool.funcSetHasErrorTrace(owner_func, true),
     }
-    return panic_func;
+    return panic_fn_index;
 }
 
 fn addSafetyCheck(
@@ -31143,6 +31154,11 @@ fn addReferenceEntry(
     referenced_unit: AnalUnit,
 ) !void {
     const zcu = sema.pt.zcu;
+    const ip = &zcu.intern_pool;
+    switch (referenced_unit.unwrap()) {
+        .func => |f| assert(ip.unwrapCoercedFunc(f) == f), // for `.{ .func = f }`, `f` must be uncoerced
+        else => {},
+    }
     if (!zcu.comp.incremental and zcu.comp.reference_trace == 0) return;
     const gop = try sema.references.getOrPut(sema.gpa, referenced_unit);
     if (gop.found_existing) return;
@@ -31329,8 +31345,9 @@ fn maybeQueueFuncBodyAnalysis(sema: *Sema, block: *Block, src: LazySrcLoc, nav_i
     const nav_val = zcu.navValue(nav_index);
     if (!ip.isFuncBody(nav_val.toIntern())) return;
 
-    try sema.addReferenceEntry(block, src, AnalUnit.wrap(.{ .func = nav_val.toIntern() }));
-    try zcu.ensureFuncBodyAnalysisQueued(nav_val.toIntern());
+    const orig_fn_index = ip.unwrapCoercedFunc(nav_val.toIntern());
+    try sema.addReferenceEntry(block, src, .wrap(.{ .func = orig_fn_index }));
+    try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
 }
 
 fn analyzeRef(
@@ -34963,8 +34980,9 @@ fn resolveInferredErrorSet(
         }
         // In this case we are dealing with the actual InferredErrorSet object that
         // corresponds to the function, not one created to track an inline/comptime call.
-        try sema.addReferenceEntry(block, src, AnalUnit.wrap(.{ .func = func_index }));
-        try pt.ensureFuncBodyUpToDate(func_index);
+        const orig_func_index = ip.unwrapCoercedFunc(func_index);
+        try sema.addReferenceEntry(block, src, .wrap(.{ .func = orig_func_index }));
+        try pt.ensureFuncBodyUpToDate(orig_func_index);
     }
 
     // This will now have been resolved by the logic at the end of `Zcu.analyzeFnBody`