fix std.mem.addNullByte and implement sentinel slicing

see #3770

lib/std/buffer.zig

@@ -82,11 +82,11 @@ pub const Buffer = struct {
     }
 
     pub fn toSlice(self: Buffer) [:0]u8 {
-        return self.list.toSlice()[0..self.len()];
+        return self.list.toSlice()[0..self.len() :0];
     }
 
     pub fn toSliceConst(self: Buffer) [:0]const u8 {
-        return self.list.toSliceConst()[0..self.len()];
+        return self.list.toSliceConst()[0..self.len() :0];
     }
 
     pub fn shrink(self: *Buffer, new_len: usize) void {

lib/std/cstr.zig

@@ -31,13 +31,21 @@ fn testCStrFnsImpl() void {
     testing.expect(mem.len(u8, "123456789") == 9);
 }
 
-/// Returns a mutable slice with 1 more byte of length which is a null byte.
+/// Returns a mutable, null-terminated slice with the same length as `slice`.
 /// Caller owns the returned memory.
 pub fn addNullByte(allocator: *mem.Allocator, slice: []const u8) ![:0]u8 {
     const result = try allocator.alloc(u8, slice.len + 1);
     mem.copy(u8, result, slice);
     result[slice.len] = 0;
-    return result;
+    return result[0..slice.len :0];
+}
+
+test "addNullByte" {
+    var buf: [30]u8 = undefined;
+    const allocator = &std.heap.FixedBufferAllocator.init(&buf).allocator;
+    const slice = try addNullByte(allocator, "hello"[0..4]);
+    testing.expect(slice.len == 4);
+    testing.expect(slice[4] == 0);
 }
 
 pub const NullTerminated2DArray = struct {

lib/std/fs.zig

@@ -221,16 +221,16 @@ pub const AtomicFile = struct {
         }
 
         tmp_path_buf[tmp_path_len] = 0;
+        const tmp_path_slice = tmp_path_buf[0..tmp_path_len :0];
 
         const my_cwd = cwd();
 
         while (true) {
             try crypto.randomBytes(rand_buf[0..]);
-            b64_fs_encoder.encode(tmp_path_buf[dirname_component_len..tmp_path_len], &rand_buf);
+            b64_fs_encoder.encode(tmp_path_slice[dirname_component_len..tmp_path_len], &rand_buf);
 
-            // TODO https://github.com/ziglang/zig/issues/3770 to clean up this @ptrCast
             const file = my_cwd.createFileC(
-                @ptrCast([*:0]u8, &tmp_path_buf),
+                tmp_path_slice, 
                 .{ .mode = mode, .exclusive = true },
             ) catch |err| switch (err) {
                 error.PathAlreadyExists => continue,
@@ -1488,8 +1488,7 @@ pub fn openSelfExe() OpenSelfExeError!File {
     var buf: [MAX_PATH_BYTES]u8 = undefined;
     const self_exe_path = try selfExePath(&buf);
     buf[self_exe_path.len] = 0;
-    // TODO avoid @ptrCast here using slice syntax with https://github.com/ziglang/zig/issues/3770
-    return openFileAbsoluteC(@ptrCast([*:0]u8, self_exe_path.ptr), .{});
+    return openFileAbsoluteC(self_exe_path[0..self_exe_path.len :0].ptr, .{});
 }
 
 test "openSelfExe" {

lib/std/mem.zig

@@ -231,9 +231,10 @@ pub const Allocator = struct {
     pub fn free(self: *Allocator, memory: var) void {
         const Slice = @typeInfo(@TypeOf(memory)).Pointer;
         const bytes = @sliceToBytes(memory);
-        if (bytes.len == 0) return;
+        const bytes_len = bytes.len + @boolToInt(Slice.sentinel != null);
+        if (bytes_len == 0) return;
         const non_const_ptr = @intToPtr([*]u8, @ptrToInt(bytes.ptr));
-        const shrink_result = self.shrinkFn(self, non_const_ptr[0..bytes.len], Slice.alignment, 0, 1);
+        const shrink_result = self.shrinkFn(self, non_const_ptr[0..bytes_len], Slice.alignment, 0, 1);
         assert(shrink_result.len == 0);
     }
 };

lib/std/os.zig

@@ -805,9 +805,9 @@ pub fn execvpeC(file: [*:0]const u8, child_argv: [*:null]const ?[*:0]const u8, e
         mem.copy(u8, &path_buf, search_path);
         path_buf[search_path.len] = '/';
         mem.copy(u8, path_buf[search_path.len + 1 ..], file_slice);
-        path_buf[search_path.len + file_slice.len + 1] = 0;
-        // TODO avoid @ptrCast here using slice syntax with https://github.com/ziglang/zig/issues/3770
-        err = execveC(@ptrCast([*:0]u8, &path_buf), child_argv, envp);
+        const path_len = search_path.len + file_slice.len + 1;
+        path_buf[path_len] = 0;
+        err = execveC(path_buf[0..path_len :0].ptr, child_argv, envp);
         switch (err) {
             error.AccessDenied => seen_eacces = true,
             error.FileNotFound, error.NotDir => {},
@@ -841,18 +841,14 @@ pub fn execvpe(
         const arg_buf = try allocator.alloc(u8, arg.len + 1);
         @memcpy(arg_buf.ptr, arg.ptr, arg.len);
         arg_buf[arg.len] = 0;
-
-        // TODO avoid @ptrCast using slice syntax with https://github.com/ziglang/zig/issues/3770
-        argv_buf[i] = @ptrCast([*:0]u8, arg_buf.ptr);
+        argv_buf[i] = arg_buf[0..arg.len :0].ptr;
     }
     argv_buf[argv_slice.len] = null;
+    const argv_ptr = argv_buf[0..argv_slice.len :null].ptr;
 
     const envp_buf = try createNullDelimitedEnvMap(allocator, env_map);
     defer freeNullDelimitedEnvMap(allocator, envp_buf);
 
-    // TODO avoid @ptrCast here using slice syntax with https://github.com/ziglang/zig/issues/3770
-    const argv_ptr = @ptrCast([*:null]?[*:0]u8, argv_buf.ptr);
-
     return execvpeC(argv_buf.ptr[0].?, argv_ptr, envp_buf.ptr);
 }
 
@@ -869,16 +865,13 @@ pub fn createNullDelimitedEnvMap(allocator: *mem.Allocator, env_map: *const std.
             @memcpy(env_buf.ptr, pair.key.ptr, pair.key.len);
             env_buf[pair.key.len] = '=';
             @memcpy(env_buf.ptr + pair.key.len + 1, pair.value.ptr, pair.value.len);
-            env_buf[env_buf.len - 1] = 0;
-
-            // TODO avoid @ptrCast here using slice syntax with https://github.com/ziglang/zig/issues/3770
-            envp_buf[i] = @ptrCast([*:0]u8, env_buf.ptr);
+            const len = env_buf.len - 1;
+            env_buf[len] = 0;
+            envp_buf[i] = env_buf[0..len :0].ptr;
         }
         assert(i == envp_count);
     }
-    // TODO avoid @ptrCast here using slice syntax with https://github.com/ziglang/zig/issues/3770
-    assert(envp_buf[envp_count] == null);
-    return @ptrCast([*:null]?[*:0]u8, envp_buf.ptr)[0..envp_count];
+    return envp_buf[0..envp_count :null];
 }
 
 pub fn freeNullDelimitedEnvMap(allocator: *mem.Allocator, envp_buf: []?[*:0]u8) void {

src/all_types.hpp

@@ -810,6 +810,7 @@ struct AstNodeSliceExpr {
     AstNode *array_ref_expr;
     AstNode *start;
     AstNode *end;
+    AstNode *sentinel; // can be null
 };
 
 struct AstNodeFieldAccessExpr {
@@ -3388,6 +3389,7 @@ struct IrInstructionSliceSrc {
     IrInstruction *ptr;
     IrInstruction *start;
     IrInstruction *end;
+    IrInstruction *sentinel;
     ResultLoc *result_loc;
 };
 

src/ir.cpp

@@ -2967,18 +2967,21 @@ static IrInstruction *ir_build_memcpy(IrBuilder *irb, Scope *scope, AstNode *sou
 }
 
 static IrInstruction *ir_build_slice_src(IrBuilder *irb, Scope *scope, AstNode *source_node,
-    IrInstruction *ptr, IrInstruction *start, IrInstruction *end, bool safety_check_on, ResultLoc *result_loc)
+    IrInstruction *ptr, IrInstruction *start, IrInstruction *end, IrInstruction *sentinel,
+    bool safety_check_on, ResultLoc *result_loc)
 {
     IrInstructionSliceSrc *instruction = ir_build_instruction<IrInstructionSliceSrc>(irb, scope, source_node);
     instruction->ptr = ptr;
     instruction->start = start;
     instruction->end = end;
+    instruction->sentinel = sentinel;
     instruction->safety_check_on = safety_check_on;
     instruction->result_loc = result_loc;
 
     ir_ref_instruction(ptr, irb->current_basic_block);
     ir_ref_instruction(start, irb->current_basic_block);
     if (end) ir_ref_instruction(end, irb->current_basic_block);
+    if (sentinel) ir_ref_instruction(sentinel, irb->current_basic_block);
 
     return &instruction->base;
 }
@@ -8483,6 +8486,7 @@ static IrInstruction *ir_gen_slice(IrBuilder *irb, Scope *scope, AstNode *node,
     AstNode *array_node = slice_expr->array_ref_expr;
     AstNode *start_node = slice_expr->start;
     AstNode *end_node = slice_expr->end;
+    AstNode *sentinel_node = slice_expr->sentinel;
 
     IrInstruction *ptr_value = ir_gen_node_extra(irb, array_node, scope, LValPtr, nullptr);
     if (ptr_value == irb->codegen->invalid_instruction)
@@ -8501,7 +8505,17 @@ static IrInstruction *ir_gen_slice(IrBuilder *irb, Scope *scope, AstNode *node,
         end_value = nullptr;
     }
 
-    IrInstruction *slice = ir_build_slice_src(irb, scope, node, ptr_value, start_value, end_value, true, result_loc);
+    IrInstruction *sentinel_value;
+    if (sentinel_node) {
+        sentinel_value = ir_gen_node(irb, sentinel_node, scope);
+        if (sentinel_value == irb->codegen->invalid_instruction)
+            return irb->codegen->invalid_instruction;
+    } else {
+        sentinel_value = nullptr;
+    }
+
+    IrInstruction *slice = ir_build_slice_src(irb, scope, node, ptr_value, start_value, end_value,
+            sentinel_value, true, result_loc);
     return ir_lval_wrap(irb, scope, slice, lval, result_loc);
 }
 
@@ -10533,6 +10547,18 @@ static ConstCastOnly types_match_const_cast_only(IrAnalyze *ira, ZigType *wanted
             result.id = ConstCastResultIdInvalid;
             return result;
         }
+        bool ok_sentinels =
+            wanted_ptr_type->data.pointer.sentinel == nullptr ||
+            (actual_ptr_type->data.pointer.sentinel != nullptr &&
+             const_values_equal(ira->codegen, wanted_ptr_type->data.pointer.sentinel,
+                 actual_ptr_type->data.pointer.sentinel));
+        if (!ok_sentinels) {
+            result.id = ConstCastResultIdPtrSentinel;
+            result.data.bad_ptr_sentinel = allocate_nonzero<ConstCastPtrSentinel>(1);
+            result.data.bad_ptr_sentinel->wanted_type = wanted_ptr_type;
+            result.data.bad_ptr_sentinel->actual_type = actual_ptr_type;
+            return result;
+        }
         if ((!actual_ptr_type->data.pointer.is_const || wanted_ptr_type->data.pointer.is_const) &&
             (!actual_ptr_type->data.pointer.is_volatile || wanted_ptr_type->data.pointer.is_volatile) &&
             actual_ptr_type->data.pointer.bit_offset_in_host == wanted_ptr_type->data.pointer.bit_offset_in_host &&
@@ -19313,6 +19339,20 @@ static ZigType *adjust_ptr_align(CodeGen *g, ZigType *ptr_type, uint32_t new_ali
             ptr_type->data.pointer.sentinel);
 }
 
+static ZigType *adjust_ptr_sentinel(CodeGen *g, ZigType *ptr_type, ZigValue *new_sentinel) {
+    assert(ptr_type->id == ZigTypeIdPointer);
+    return get_pointer_to_type_extra2(g,
+            ptr_type->data.pointer.child_type,
+            ptr_type->data.pointer.is_const, ptr_type->data.pointer.is_volatile,
+            ptr_type->data.pointer.ptr_len,
+            ptr_type->data.pointer.explicit_alignment,
+            ptr_type->data.pointer.bit_offset_in_host, ptr_type->data.pointer.host_int_bytes,
+            ptr_type->data.pointer.allow_zero,
+            ptr_type->data.pointer.vector_index,
+            ptr_type->data.pointer.inferred_struct_field,
+            new_sentinel);
+}
+
 static ZigType *adjust_slice_align(CodeGen *g, ZigType *slice_type, uint32_t new_align) {
     assert(is_slice(slice_type));
     ZigType *ptr_type = adjust_ptr_align(g, slice_type->data.structure.fields[slice_ptr_index]->type_entry,
@@ -25051,50 +25091,70 @@ static IrInstruction *ir_analyze_instruction_slice(IrAnalyze *ira, IrInstruction
         end = nullptr;
     }
 
-    ZigType *return_type;
+    ZigType *non_sentinel_slice_ptr_type;
+    ZigType *elem_type;
 
     if (array_type->id == ZigTypeIdArray) {
+        elem_type = array_type->data.array.child_type;
         bool is_comptime_const = ptr_ptr->value->special == ConstValSpecialStatic &&
             ptr_ptr->value->data.x_ptr.mut == ConstPtrMutComptimeConst;
-        ZigType *slice_ptr_type = get_pointer_to_type_extra(ira->codegen, array_type->data.array.child_type,
+        non_sentinel_slice_ptr_type = get_pointer_to_type_extra(ira->codegen, elem_type,
             ptr_ptr_type->data.pointer.is_const || is_comptime_const,
             ptr_ptr_type->data.pointer.is_volatile,
             PtrLenUnknown,
             ptr_ptr_type->data.pointer.explicit_alignment, 0, 0, false);
-        return_type = get_slice_type(ira->codegen, slice_ptr_type);
     } else if (array_type->id == ZigTypeIdPointer) {
         if (array_type->data.pointer.ptr_len == PtrLenSingle) {
             ZigType *main_type = array_type->data.pointer.child_type;
             if (main_type->id == ZigTypeIdArray) {
-                ZigType *slice_ptr_type = get_pointer_to_type_extra(ira->codegen,
-                        main_type->data.pointer.child_type,
+                elem_type = main_type->data.pointer.child_type;
+                non_sentinel_slice_ptr_type = get_pointer_to_type_extra(ira->codegen,
+                        elem_type,
                         array_type->data.pointer.is_const, array_type->data.pointer.is_volatile,
                         PtrLenUnknown,
                         array_type->data.pointer.explicit_alignment, 0, 0, false);
-                return_type = get_slice_type(ira->codegen, slice_ptr_type);
             } else {
                 ir_add_error(ira, &instruction->base, buf_sprintf("slice of single-item pointer"));
                 return ira->codegen->invalid_instruction;
             }
         } else {
+            elem_type = array_type->data.pointer.child_type;
             if (array_type->data.pointer.ptr_len == PtrLenC) {
                 array_type = adjust_ptr_len(ira->codegen, array_type, PtrLenUnknown);
             }
-            return_type = get_slice_type(ira->codegen, array_type);
+            non_sentinel_slice_ptr_type = array_type;
             if (!end) {
                 ir_add_error(ira, &instruction->base, buf_sprintf("slice of pointer must include end value"));
                 return ira->codegen->invalid_instruction;
             }
         }
     } else if (is_slice(array_type)) {
-        ZigType *ptr_type = array_type->data.structure.fields[slice_ptr_index]->type_entry;
-        return_type = get_slice_type(ira->codegen, ptr_type);
+        non_sentinel_slice_ptr_type = array_type->data.structure.fields[slice_ptr_index]->type_entry;
+        elem_type = non_sentinel_slice_ptr_type->data.pointer.child_type;
     } else {
         ir_add_error(ira, &instruction->base,
             buf_sprintf("slice of non-array type '%s'", buf_ptr(&array_type->name)));
         return ira->codegen->invalid_instruction;
     }
 
+    ZigType *return_type;
+    ZigValue *sentinel_val = nullptr;
+    if (instruction->sentinel) {
+        IrInstruction *uncasted_sentinel = instruction->sentinel->child;
+        if (type_is_invalid(uncasted_sentinel->value->type))
+            return ira->codegen->invalid_instruction;
+        IrInstruction *sentinel = ir_implicit_cast(ira, uncasted_sentinel, elem_type);
+        if (type_is_invalid(sentinel->value->type))
+            return ira->codegen->invalid_instruction;
+        sentinel_val = ir_resolve_const(ira, sentinel, UndefBad);
+        if (sentinel_val == nullptr)
+            return ira->codegen->invalid_instruction;
+        ZigType *slice_ptr_type = adjust_ptr_sentinel(ira->codegen, non_sentinel_slice_ptr_type, sentinel_val);
+        return_type = get_slice_type(ira->codegen, slice_ptr_type);
+    } else {
+        return_type = get_slice_type(ira->codegen, non_sentinel_slice_ptr_type);
+    }
+
     if (instr_is_comptime(ptr_ptr) &&
         value_is_comptime(casted_start->value) &&
         (!end || value_is_comptime(end->value)))

src/parser.cpp

@@ -2723,7 +2723,7 @@ static AstNode *ast_parse_prefix_type_op(ParseContext *pc) {
 }
 
 // SuffixOp
-//     <- LBRACKET Expr (DOT2 Expr?)? RBRACKET
+//     <- LBRACKET Expr (DOT2 (Expr (COLON Expr)?)?)? RBRACKET
 //      / DOT IDENTIFIER
 //      / DOTASTERISK
 //      / DOTQUESTIONMARK
@@ -2733,12 +2733,17 @@ static AstNode *ast_parse_suffix_op(ParseContext *pc) {
         AstNode *start = ast_expect(pc, ast_parse_expr);
         AstNode *end = nullptr;
         if (eat_token_if(pc, TokenIdEllipsis2) != nullptr) {
+            AstNode *sentinel = nullptr;
             end = ast_parse_expr(pc);
+            if (eat_token_if(pc, TokenIdColon) != nullptr) {
+                sentinel = ast_parse_expr(pc);
+            }
             expect_token(pc, TokenIdRBracket);
 
             AstNode *res = ast_create_node(pc, NodeTypeSliceExpr, lbracket);
             res->data.slice_expr.start = start;
             res->data.slice_expr.end = end;
+            res->data.slice_expr.sentinel = sentinel;
             return res;
         }
 
@@ -3041,6 +3046,7 @@ void ast_visit_node_children(AstNode *node, void (*visit)(AstNode **, void *cont
             visit_field(&node->data.slice_expr.array_ref_expr, visit, context);
             visit_field(&node->data.slice_expr.start, visit, context);
             visit_field(&node->data.slice_expr.end, visit, context);
+            visit_field(&node->data.slice_expr.sentinel, visit, context);
             break;
         case NodeTypeFieldAccessExpr:
             visit_field(&node->data.field_access_expr.struct_expr, visit, context);

test/compile_errors.zig

@@ -2,6 +2,17 @@ const tests = @import("tests.zig");
 const builtin = @import("builtin");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.add("slice sentinel mismatch",
+        \\fn foo() [:0]u8 {
+        \\    var x: []u8 = undefined;
+        \\    return x;
+        \\}
+        \\comptime { _ = foo; }
+    , &[_][]const u8{
+        "tmp.zig:3:12: error: expected type '[:0]u8', found '[]u8'",
+        "tmp.zig:3:12: note: destination pointer requires a terminating '0' sentinel",
+    });
+
     cases.add("intToPtr with misaligned address",
         \\pub fn main() void {
         \\    var y = @intToPtr([*]align(4) u8, 5);