Merge pull request #3652 from ziglang/anon-container-lit

implement anonymous struct literals and anonymous list literals

doc/langref.html.in

@@ -1734,6 +1734,43 @@ test "array initialization with function calls" {
       {#code_end#}
       {#see_also|for|Slices#}
 
+      {#header_open|Anonymous List Literals#}
+      <p>Similar to {#link|Enum Literals#} and {#link|Anonymous Struct Literals#}
+      the type can be omitted from array literals:</p>
+      {#code_begin|test|anon_list#}
+const std = @import("std");
+const assert = std.debug.assert;
+
+test "anonymous list literal syntax" {
+    var array: [4]u8 = .{11, 22, 33, 44};
+    assert(array[0] == 11);
+    assert(array[1] == 22);
+    assert(array[2] == 33);
+    assert(array[3] == 44);
+}
+      {#code_end#}
+      <p>
+      If there is no type in the result location then an anonymous list literal actually
+      turns into a {#link|struct#} with numbered field names:
+      </p>
+      {#code_begin|test|infer_list_literal#}
+const std = @import("std");
+const assert = std.debug.assert;
+
+test "fully anonymous list literal" {
+    dump(.{ @as(u32, 1234), @as(f64, 12.34), true, "hi"});
+}
+
+fn dump(args: var) void {
+    assert(args.@"0" == 1234);
+    assert(args.@"1" == 12.34);
+    assert(args.@"2");
+    assert(args.@"3"[0] == 'h');
+    assert(args.@"3"[1] == 'i');
+}
+      {#code_end#}
+      {#header_close#}
+
       {#header_open|Multidimensional Arrays#}
       <p>
       Mutlidimensional arrays can be created by nesting arrays:
@@ -2526,7 +2563,8 @@ test "overaligned pointer to packed struct" {
       Don't worry, there will be a good solution for this use case in zig.
       </p>
       {#header_close#}
-      {#header_open|struct Naming#}
+
+      {#header_open|Struct Naming#}
       <p>Since all structs are anonymous, Zig infers the type name based on a few rules.</p>
       <ul>
           <li>If the struct is in the initialization expression of a variable, it gets named after
@@ -2552,6 +2590,53 @@ fn List(comptime T: type) type {
 }
       {#code_end#}
       {#header_close#}
+
+      {#header_open|Anonymous Struct Literals#}
+      <p>
+      Zig allows omitting the struct type of a literal. When the result is {#link|coerced|Type Coercion#},
+      the struct literal will directly instantiate the result location, with no copy:
+      </p>
+      {#code_begin|test|struct_result#}
+const std = @import("std");
+const assert = std.debug.assert;
+
+const Point = struct {x: i32, y: i32};
+
+test "anonymous struct literal" {
+    var pt: Point = .{
+        .x = 13,
+        .y = 67,
+    };
+    assert(pt.x == 13);
+    assert(pt.y == 67);
+}
+      {#code_end#}
+      <p>
+      The struct type can be inferred. Here the result location does not include a type, and
+      so Zig infers the type:
+      </p>
+      {#code_begin|test|struct_anon#}
+const std = @import("std");
+const assert = std.debug.assert;
+
+test "fully anonymous struct" {
+    dump(.{
+        .int = @as(u32, 1234),
+        .float = @as(f64, 12.34),
+        .b = true,
+        .s = "hi",
+    });
+}
+
+fn dump(args: var) void {
+    assert(args.int == 1234);
+    assert(args.float == 12.34);
+    assert(args.b);
+    assert(args.s[0] == 'h');
+    assert(args.s[1] == 'i');
+}
+      {#code_end#}
+      {#header_close#}
       {#see_also|comptime|@fieldParentPtr#}
       {#header_close#}
       {#header_open|enum#}
@@ -2906,6 +2991,32 @@ test "@tagName" {
       <p>A {#syntax#}packed union{#endsyntax#} has well-defined in-memory layout and is eligible
       to be in a {#link|packed struct#}.
       {#header_close#}
+
+      {#header_open|Anonymous Union Literals#}
+      <p>{#link|Anonymous Struct Literals#} syntax can be used to initialize unions without specifying
+      the type:</p>
+      {#code_begin|test|anon_union#}
+const std = @import("std");
+const assert = std.debug.assert;
+
+const Number = union {
+    int: i32,
+    float: f64,
+};
+
+test "anonymous union literal syntax" {
+    var i: Number = .{.int = 42};
+    var f = makeNumber();
+    assert(i.int == 42);
+    assert(f.float == 12.34);
+}
+
+fn makeNumber() Number {
+    return .{.float = 12.34};
+}
+      {#code_end#}
+      {#header_close#}
+
       {#header_close#}
 
       {#header_open|blocks#}

lib/std/builtin.zig

@@ -90,40 +90,11 @@ pub const Mode = enum {
     ReleaseSmall,
 };
 
-/// This data structure is used by the Zig language code generation and
-/// therefore must be kept in sync with the compiler implementation.
-pub const TypeId = enum {
-    Type,
-    Void,
-    Bool,
-    NoReturn,
-    Int,
-    Float,
-    Pointer,
-    Array,
-    Struct,
-    ComptimeFloat,
-    ComptimeInt,
-    Undefined,
-    Null,
-    Optional,
-    ErrorUnion,
-    ErrorSet,
-    Enum,
-    Union,
-    Fn,
-    BoundFn,
-    ArgTuple,
-    Opaque,
-    Frame,
-    AnyFrame,
-    Vector,
-    EnumLiteral,
-};
+pub const TypeId = @TagType(TypeInfo);
 
 /// This data structure is used by the Zig language code generation and
 /// therefore must be kept in sync with the compiler implementation.
-pub const TypeInfo = union(TypeId) {
+pub const TypeInfo = union(enum) {
     Type: void,
     Void: void,
     Bool: void,

lib/std/zig/ast.zig

@@ -1648,10 +1648,15 @@ pub const Node = struct {
 
     pub const SuffixOp = struct {
         base: Node,
-        lhs: *Node,
+        lhs: Lhs,
         op: Op,
         rtoken: TokenIndex,
 
+        pub const Lhs = union(enum) {
+            node: *Node,
+            dot: TokenIndex,
+        };
+
         pub const Op = union(enum) {
             Call: Call,
             ArrayAccess: *Node,
@@ -1679,8 +1684,13 @@ pub const Node = struct {
         pub fn iterate(self: *SuffixOp, index: usize) ?*Node {
             var i = index;
 
-            if (i < 1) return self.lhs;
-            i -= 1;
+            switch (self.lhs) {
+                .node => |node| {
+                    if (i == 0) return node;
+                    i -= 1;
+                },
+                .dot => {},
+            }
 
             switch (self.op) {
                 .Call => |*call_info| {
@@ -1721,7 +1731,10 @@ pub const Node = struct {
                 .Call => |*call_info| if (call_info.async_token) |async_token| return async_token,
                 else => {},
             }
-            return self.lhs.firstToken();
+            switch (self.lhs) {
+                .node => |node| return node.firstToken(),
+                .dot => |dot| return dot,
+            }
         }
 
         pub fn lastToken(self: *const SuffixOp) TokenIndex {

lib/std/zig/parse.zig

@@ -1026,16 +1026,16 @@ fn parseWhileExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
 /// CurlySuffixExpr <- TypeExpr InitList?
 fn parseCurlySuffixExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
     const type_expr = (try parseTypeExpr(arena, it, tree)) orelse return null;
-    const init_list = (try parseInitList(arena, it, tree)) orelse return type_expr;
-    init_list.cast(Node.SuffixOp).?.lhs = type_expr;
-    return init_list;
+    const suffix_op = (try parseInitList(arena, it, tree)) orelse return type_expr;
+    suffix_op.lhs.node = type_expr;
+    return &suffix_op.base;
 }
 
 /// InitList
 ///     <- LBRACE FieldInit (COMMA FieldInit)* COMMA? RBRACE
 ///      / LBRACE Expr (COMMA Expr)* COMMA? RBRACE
 ///      / LBRACE RBRACE
-fn parseInitList(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
+fn parseInitList(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node.SuffixOp {
     const lbrace = eatToken(it, .LBrace) orelse return null;
     var init_list = Node.SuffixOp.Op.InitList.init(arena);
 
@@ -1064,11 +1064,11 @@ fn parseInitList(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
     const node = try arena.create(Node.SuffixOp);
     node.* = Node.SuffixOp{
         .base = Node{ .id = .SuffixOp },
-        .lhs = undefined, // set by caller
+        .lhs = .{.node = undefined}, // set by caller
         .op = op,
         .rtoken = try expectToken(it, tree, .RBrace),
     };
-    return &node.base;
+    return node;
 }
 
 /// TypeExpr <- PrefixTypeOp* ErrorUnionExpr
@@ -1117,7 +1117,7 @@ fn parseSuffixExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
 
         while (try parseSuffixOp(arena, it, tree)) |node| {
             switch (node.id) {
-                .SuffixOp => node.cast(Node.SuffixOp).?.lhs = res,
+                .SuffixOp => node.cast(Node.SuffixOp).?.lhs = .{.node = res},
                 .InfixOp => node.cast(Node.InfixOp).?.lhs = res,
                 else => unreachable,
             }
@@ -1133,7 +1133,7 @@ fn parseSuffixExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
         const node = try arena.create(Node.SuffixOp);
         node.* = Node.SuffixOp{
             .base = Node{ .id = .SuffixOp },
-            .lhs = res,
+            .lhs = .{.node = res},
             .op = Node.SuffixOp.Op{
                 .Call = Node.SuffixOp.Op.Call{
                     .params = params.list,
@@ -1150,7 +1150,7 @@ fn parseSuffixExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
         while (true) {
             if (try parseSuffixOp(arena, it, tree)) |node| {
                 switch (node.id) {
-                    .SuffixOp => node.cast(Node.SuffixOp).?.lhs = res,
+                    .SuffixOp => node.cast(Node.SuffixOp).?.lhs = .{.node = res},
                     .InfixOp => node.cast(Node.InfixOp).?.lhs = res,
                     else => unreachable,
                 }
@@ -1161,7 +1161,7 @@ fn parseSuffixExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
                 const call = try arena.create(Node.SuffixOp);
                 call.* = Node.SuffixOp{
                     .base = Node{ .id = .SuffixOp },
-                    .lhs = res,
+                    .lhs = .{.node = res},
                     .op = Node.SuffixOp.Op{
                         .Call = Node.SuffixOp.Op.Call{
                             .params = params.list,
@@ -1215,7 +1215,7 @@ fn parsePrimaryTypeExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*N
         return &node.base;
     }
     if (try parseContainerDecl(arena, it, tree)) |node| return node;
-    if (try parseEnumLiteral(arena, it, tree)) |node| return node;
+    if (try parseAnonLiteral(arena, it, tree)) |node| return node;
     if (try parseErrorSetDecl(arena, it, tree)) |node| return node;
     if (try parseFloatLiteral(arena, it, tree)) |node| return node;
     if (try parseFnProto(arena, it, tree)) |node| return node;
@@ -1494,16 +1494,28 @@ fn parseAsmExpr(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
 }
 
 /// DOT IDENTIFIER
-fn parseEnumLiteral(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
+fn parseAnonLiteral(arena: *Allocator, it: *TokenIterator, tree: *Tree) !?*Node {
     const dot = eatToken(it, .Period) orelse return null;
-    const name = try expectToken(it, tree, .Identifier);
-    const node = try arena.create(Node.EnumLiteral);
-    node.* = Node.EnumLiteral{
-        .base = Node{ .id = .EnumLiteral },
-        .dot = dot,
-        .name = name,
-    };
-    return &node.base;
+
+    // anon enum literal
+    if (eatToken(it, .Identifier)) |name| {
+        const node = try arena.create(Node.EnumLiteral);
+        node.* = Node.EnumLiteral{
+            .base = Node{ .id = .EnumLiteral },
+            .dot = dot,
+            .name = name,
+        };
+        return &node.base;
+    }
+
+    // anon container literal
+    if (try parseInitList(arena, it, tree)) |node| {
+        node.lhs = .{.dot = dot};
+        return &node.base;
+    }
+
+    putBackToken(it, dot);
+    return null;
 }
 
 /// AsmOutput <- COLON AsmOutputList AsmInput?

lib/std/zig/parser_test.zig

@@ -1,3 +1,20 @@
+test "zig fmt: anon struct literal syntax" {
+    try testCanonical(
+        \\const x = .{
+        \\    .a = b,
+        \\    .c = d,
+        \\};
+        \\
+    );
+}
+
+test "zig fmt: anon list literal syntax" {
+    try testCanonical(
+        \\const x = .{ a, b, c };
+        \\
+    );
+}
+
 test "zig fmt: async function" {
     try testCanonical(
         \\pub const Server = struct {