std: have std.meta.fieldInfo take an enum rather than a string

lib/std/meta.zig

@@ -487,19 +487,14 @@ test "std.meta.fields" {
     testing.expect(comptime uf[0].field_type == u8);
 }
 
-pub fn fieldInfo(comptime T: type, comptime field_name: []const u8) switch (@typeInfo(T)) {
+pub fn fieldInfo(comptime T: type, comptime field: FieldEnum(T)) switch (@typeInfo(T)) {
     .Struct => TypeInfo.StructField,
     .Union => TypeInfo.UnionField,
     .ErrorSet => TypeInfo.Error,
     .Enum => TypeInfo.EnumField,
     else => @compileError("Expected struct, union, error set or enum type, found '" ++ @typeName(T) ++ "'"),
 } {
-    inline for (comptime fields(T)) |field| {
-        if (comptime mem.eql(u8, field.name, field_name))
-            return field;
-    }
-
-    @compileError("'" ++ @typeName(T) ++ "' has no field '" ++ field_name ++ "'");
+    return fields(T)[@enumToInt(field)];
 }
 
 test "std.meta.fieldInfo" {
@@ -514,10 +509,10 @@ test "std.meta.fieldInfo" {
         a: u8,
     };
 
-    const e1f = comptime fieldInfo(E1, "A");
-    const e2f = comptime fieldInfo(E2, "A");
-    const sf = comptime fieldInfo(S1, "a");
-    const uf = comptime fieldInfo(U1, "a");
+    const e1f = fieldInfo(E1, .A);
+    const e2f = fieldInfo(E2, .A);
+    const sf = fieldInfo(S1, .a);
+    const uf = fieldInfo(U1, .a);
 
     testing.expect(mem.eql(u8, e1f.name, "A"));
     testing.expect(mem.eql(u8, e2f.name, "A"));

lib/std/zig/ast.zig

@@ -688,7 +688,7 @@ pub const Node = struct {
 
     /// Prefer `castTag` to this.
     pub fn cast(base: *Node, comptime T: type) ?*T {
-        if (std.meta.fieldInfo(T, "base").default_value) |default_base| {
+        if (std.meta.fieldInfo(T, .base).default_value) |default_base| {
             return base.castTag(default_base.tag);
         }
         inline for (@typeInfo(Tag).Enum.fields) |field| {

src/astgen.zig

@@ -758,7 +758,7 @@ fn ptrSliceType(mod: *Module, scope: *Scope, src: usize, ptr_info: *ast.PtrInfo,
         }, child_type);
     }
 
-    var kw_args: std.meta.fieldInfo(zir.Inst.PtrType, "kw_args").field_type = .{};
+    var kw_args: std.meta.fieldInfo(zir.Inst.PtrType, .kw_args).field_type = .{};
     kw_args.size = size;
     kw_args.@"allowzero" = ptr_info.allowzero_token != null;
     if (ptr_info.align_info) |some| {
@@ -2756,8 +2756,8 @@ pub fn addZIRInstSpecial(
     scope: *Scope,
     src: usize,
     comptime T: type,
-    positionals: std.meta.fieldInfo(T, "positionals").field_type,
-    kw_args: std.meta.fieldInfo(T, "kw_args").field_type,
+    positionals: std.meta.fieldInfo(T, .positionals).field_type,
+    kw_args: std.meta.fieldInfo(T, .kw_args).field_type,
 ) !*T {
     const gen_zir = scope.getGenZIR();
     try gen_zir.instructions.ensureCapacity(mod.gpa, gen_zir.instructions.items.len + 1);
@@ -2874,8 +2874,8 @@ pub fn addZIRInst(
     scope: *Scope,
     src: usize,
     comptime T: type,
-    positionals: std.meta.fieldInfo(T, "positionals").field_type,
-    kw_args: std.meta.fieldInfo(T, "kw_args").field_type,
+    positionals: std.meta.fieldInfo(T, .positionals).field_type,
+    kw_args: std.meta.fieldInfo(T, .kw_args).field_type,
 ) !*zir.Inst {
     const inst_special = try addZIRInstSpecial(mod, scope, src, T, positionals, kw_args);
     return &inst_special.base;
@@ -2883,12 +2883,12 @@ pub fn addZIRInst(
 
 /// TODO The existence of this function is a workaround for a bug in stage1.
 pub fn addZIRInstConst(mod: *Module, scope: *Scope, src: usize, typed_value: TypedValue) !*zir.Inst {
-    const P = std.meta.fieldInfo(zir.Inst.Const, "positionals").field_type;
+    const P = std.meta.fieldInfo(zir.Inst.Const, .positionals).field_type;
     return addZIRInst(mod, scope, src, zir.Inst.Const, P{ .typed_value = typed_value }, .{});
 }
 
 /// TODO The existence of this function is a workaround for a bug in stage1.
 pub fn addZIRInstLoop(mod: *Module, scope: *Scope, src: usize, body: zir.Module.Body) !*zir.Inst.Loop {
-    const P = std.meta.fieldInfo(zir.Inst.Loop, "positionals").field_type;
+    const P = std.meta.fieldInfo(zir.Inst.Loop, .positionals).field_type;
     return addZIRInstSpecial(mod, scope, src, zir.Inst.Loop, P{ .body = body }, .{});
 }

src/ir.zig

@@ -189,7 +189,7 @@ pub const Inst = struct {
     }
 
     pub fn Args(comptime T: type) type {
-        return std.meta.fieldInfo(T, "args").field_type;
+        return std.meta.fieldInfo(T, .args).field_type;
     }
 
     /// Returns `null` if runtime-known.

src/type.zig

@@ -3232,7 +3232,7 @@ pub const Type = extern union {
         }
 
         pub fn Data(comptime t: Tag) type {
-            return std.meta.fieldInfo(t.Type(), "data").field_type;
+            return std.meta.fieldInfo(t.Type(), .data).field_type;
         }
     };
 

src/value.zig

@@ -207,7 +207,7 @@ pub const Value = extern union {
         }
 
         pub fn Data(comptime t: Tag) type {
-            return std.meta.fieldInfo(t.Type(), "data").field_type;
+            return std.meta.fieldInfo(t.Type(), .data).field_type;
         }
     };