stage2: various fixes to get one test passing

* resolve error sets before merging them
* implement tupleFieldPtr
* make ret_ptr behave like alloc with zero sized types in llvm backend

src/Module.zig

@@ -1435,7 +1435,7 @@ pub const Fn = struct {
         /// All currently known errors that this error set contains. This includes direct additions
         /// via `return error.Foo;`, and possibly also errors that are returned from any dependent functions.
         /// When the inferred error set is fully resolved, this map contains all the errors that the function might return.
-        errors: std.StringHashMapUnmanaged(void) = .{},
+        errors: ErrorSet.NameMap = .{},
 
         /// Other inferred error sets which this inferred error set should include.
         inferred_error_sets: std.AutoHashMapUnmanaged(*InferredErrorSet, void) = .{},

src/Sema.zig

@@ -1613,11 +1613,16 @@ fn zirCoerceResultPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileE
         //}
 
         // The last one is always `store`.
-        const trash_inst = trash_block.instructions.pop();
+        const trash_inst = trash_block.instructions.items[trash_block.instructions.items.len - 1];
-        assert(air_tags[trash_inst] == .store);
+        if (air_tags[trash_inst] != .store) {
+            // no store instruction is generated for zero sized types
+            assert((try sema.typeHasOnePossibleValue(block, src, pointee_ty)) != null);
+        } else {
+            trash_block.instructions.items.len -= 1;
             assert(trash_inst == sema.air_instructions.len - 1);
             sema.air_instructions.len -= 1;
         }
+    }
 
     const ptr_ty = try Type.ptr(sema.arena, .{
         .pointee_type = pointee_ty,
@@ -5236,6 +5241,22 @@ fn zirMergeErrorSets(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileEr
     if (lhs_ty.tag() == .anyerror or rhs_ty.tag() == .anyerror) {
         return Air.Inst.Ref.anyerror_type;
     }
+
+    if (lhs_ty.castTag(.error_set_inferred)) |payload| {
+        try sema.resolveInferredErrorSet(payload.data);
+        // isAnyError might have changed from a false negative to a true positive after resolution.
+        if (lhs_ty.isAnyError()) {
+            return Air.Inst.Ref.anyerror_type;
+        }
+    }
+    if (rhs_ty.castTag(.error_set_inferred)) |payload| {
+        try sema.resolveInferredErrorSet(payload.data);
+        // isAnyError might have changed from a false negative to a true positive after resolution.
+        if (rhs_ty.isAnyError()) {
+            return Air.Inst.Ref.anyerror_type;
+        }
+    }
+
     // Resolve both error sets now.
     const lhs_names = lhs_ty.errorSetNames();
     const rhs_names = rhs_ty.errorSetNames();
@@ -6809,6 +6830,10 @@ fn zirSwitchBlock(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError
                 }
             }
 
+            if (operand_ty.castTag(.error_set_inferred)) |inferred| {
+                try sema.resolveInferredErrorSet(inferred.data);
+            }
+
             if (operand_ty.isAnyError()) {
                 if (special_prong != .@"else") {
                     return sema.fail(
@@ -14597,6 +14622,12 @@ fn elemPtr(
         },
         .Array => return sema.elemPtrArray(block, array_ptr_src, array_ptr, elem_index, elem_index_src),
         .Vector => return sema.fail(block, src, "TODO implement Sema for elemPtr for vector", .{}),
+        .Struct => {
+            // Tuple field access.
+            const index_val = try sema.resolveConstValue(block, elem_index_src, elem_index);
+            const index = @intCast(u32, index_val.toUnsignedInt());
+            return sema.tupleFieldPtr(block, array_ptr, index, src, elem_index_src);
+        },
         else => unreachable,
     }
 }
@@ -14673,6 +14704,45 @@ fn elemVal(
     }
 }
 
+fn tupleFieldPtr(
+    sema: *Sema,
+    block: *Block,
+    tuple_ptr: Air.Inst.Ref,
+    field_index: u32,
+    tuple_src: LazySrcLoc,
+    field_index_src: LazySrcLoc,
+) CompileError!Air.Inst.Ref {
+    const tuple_ptr_ty = sema.typeOf(tuple_ptr);
+    const tuple_ty = tuple_ptr_ty.childType();
+    const tuple_info = tuple_ty.castTag(.tuple).?.data;
+
+    if (field_index > tuple_info.types.len) {
+        return sema.fail(block, field_index_src, "index {d} outside tuple of length {d}", .{
+            field_index, tuple_info.types.len,
+        });
+    }
+
+    const field_ty = tuple_info.types[field_index];
+    const ptr_field_ty = try Type.ptr(sema.arena, .{
+        .pointee_type = field_ty,
+        .mutable = tuple_ptr_ty.ptrIsMutable(),
+        .@"addrspace" = tuple_ptr_ty.ptrAddressSpace(),
+    });
+
+    if (try sema.resolveMaybeUndefVal(block, tuple_src, tuple_ptr)) |tuple_ptr_val| {
+        return sema.addConstant(
+            ptr_field_ty,
+            try Value.Tag.field_ptr.create(sema.arena, .{
+                .container_ptr = tuple_ptr_val,
+                .field_index = field_index,
+            }),
+        );
+    }
+
+    try sema.requireRuntimeBlock(block, tuple_src);
+    return block.addStructFieldPtr(tuple_ptr, field_index, ptr_field_ty);
+}
+
 fn tupleField(
     sema: *Sema,
     block: *Block,
@@ -15273,9 +15343,8 @@ fn coerceInMemoryAllowedErrorSets(
                 return .no_match;
             }
 
-            var it = src_data.errors.keyIterator();
+            for (src_data.errors.keys()) |key| {
-            while (it.next()) |name_ptr| {
+                if (!dest_ty.errorSetHasField(key)) {
-                if (!dest_ty.errorSetHasField(name_ptr.*)) {
                     return .no_match;
                 }
             }
@@ -17525,9 +17594,8 @@ fn resolveInferredErrorSet(sema: *Sema, inferred_error_set: *Module.Fn.InferredE
         try sema.ensureDeclAnalyzed(decl); // To ensure that all dependencies are properly added to the set.
         try sema.resolveInferredErrorSet(other_error_set_ptr.*);
 
-        var error_it = other_error_set_ptr.*.errors.keyIterator();
+        for (other_error_set_ptr.*.errors.keys()) |key| {
-        while (error_it.next()) |entry| {
+            try inferred_error_set.errors.put(sema.gpa, key, {});
-            try inferred_error_set.errors.put(sema.gpa, entry.*, {});
         }
         if (other_error_set_ptr.*.is_anyerror)
             inferred_error_set.is_anyerror = true;

src/codegen/llvm.zig

@@ -4025,7 +4025,7 @@ pub const FuncGen = struct {
         if (self.liveness.isUnused(inst)) return null;
         const ptr_ty = self.air.typeOfIndex(inst);
         const ret_ty = ptr_ty.childType();
-        if (!ret_ty.isFnOrHasRuntimeBits()) return null;
+        if (!ret_ty.isFnOrHasRuntimeBits()) return self.dg.lowerPtrToVoid(ptr_ty);
         if (self.ret_ptr) |ret_ptr| return ret_ptr;
         const ret_llvm_ty = try self.dg.llvmType(ret_ty);
         const target = self.dg.module.getTarget();
@@ -4845,6 +4845,7 @@ pub const FuncGen = struct {
         struct_ptr_ty: Type,
         field_index: u32,
     ) !?*const llvm.Value {
+        if (self.liveness.isUnused(inst)) return null;
         const struct_ty = struct_ptr_ty.childType();
         switch (struct_ty.zigTypeTag()) {
             .Struct => switch (struct_ty.containerLayout()) {

src/type.zig

@@ -3878,6 +3878,12 @@ pub const Type = extern union {
             },
             .error_set_merged => ty.castTag(.error_set_merged).?.data.keys(),
             .error_set => ty.castTag(.error_set).?.data.names.keys(),
+            .error_set_inferred => {
+                const inferred_error_set = ty.castTag(.error_set_inferred).?.data;
+                assert(inferred_error_set.is_resolved);
+                assert(!inferred_error_set.is_anyerror);
+                return inferred_error_set.errors.keys();
+            },
             else => unreachable,
         };
     }

test/behavior.zig

@@ -132,6 +132,7 @@ test {
             _ = @import("behavior/bugs/3384.zig");
             _ = @import("behavior/bugs/3742.zig");
             _ = @import("behavior/bugs/5398.zig");
+            _ = @import("behavior/bugs/5487.zig");
             _ = @import("behavior/struct_contains_null_ptr_itself.zig");
             _ = @import("behavior/switch_prong_err_enum.zig");
             _ = @import("behavior/switch_prong_implicit_cast.zig");
@@ -153,7 +154,6 @@ test {
                 _ = @import("behavior/bugs/1851.zig");
                 _ = @import("behavior/bugs/3779.zig");
                 _ = @import("behavior/bugs/5413.zig");
-                _ = @import("behavior/bugs/5487.zig");
                 _ = @import("behavior/bugs/6456.zig");
                 _ = @import("behavior/bugs/6781.zig");
                 _ = @import("behavior/bugs/7003.zig");