From 02c3af2432cf8f764f450080b73a86d48965c5b1 Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Sat, 29 Oct 2022 06:32:20 +0300
Subject: [PATCH] all: add support for `enum Xyz as u64 {` + tests (#16246)

---
 doc/docs.md                                   |   4 +-
 make.bat                                      |   2 +-
 vlib/sokol/gfx/enums.v                        |   2 +-
 vlib/v/ast/ast.v                              |   1 +
 vlib/v/checker/checker.v                      | 160 ++++++++++++++----
 vlib/v/checker/tests/enum_err.out             |   4 +-
 .../tests/enum_field_name_duplicate_err.out   |   2 +-
 vlib/v/checker/tests/enum_field_overflow.out  |  11 +-
 .../tests/enum_field_value_overflow.out       |  87 +++++++++-
 .../tests/enum_field_value_overflow.vv        |  64 +++++++
 vlib/v/fmt/fmt.v                              |   6 +-
 vlib/v/gen/c/auto_str_methods.v               |   4 +-
 vlib/v/gen/c/cgen.v                           |  38 ++++-
 vlib/v/gen/native/tests/enum.vv               |   5 +-
 vlib/v/gen/native/tests/enum.vv.out           |   1 +
 vlib/v/parser/parser.v                        |  23 ++-
 vlib/v/tests/enum_bitfield_64bit_test.v       | 124 ++++++++++++++
 .../enum_explicit_size_big_and_small_test.v   |  83 +++++++++
 18 files changed, 567 insertions(+), 54 deletions(-)
 create mode 100644 vlib/v/tests/enum_bitfield_64bit_test.v
 create mode 100644 vlib/v/tests/enum_explicit_size_big_and_small_test.v

diff --git a/doc/docs.md b/doc/docs.md
index 21396f980d..59feee51df 100644
--- a/doc/docs.md
+++ b/doc/docs.md
@@ -3237,7 +3237,7 @@ You can see the complete
 ### Enums
 
 ```v
-enum Color {
+enum Color as u8 {
 	red
 	green
 	blue
@@ -3254,6 +3254,8 @@ match color {
 }
 ```
 
+The enum type can be any integer type, but can be ommited, if it is `int`: `enum Color {`.
+
 Enum match must be exhaustive or have an `else` branch.
 This ensures that if a new enum field is added, it's handled everywhere in the code.
 
diff --git a/make.bat b/make.bat
index 2c7f20c0a0..feb5845fcf 100644
--- a/make.bat
+++ b/make.bat
@@ -205,7 +205,7 @@ if exist "%InstallDir%\Common7\Tools\vsdevcmd.bat" (
 set ObjFile=.v.c.obj
 
 echo  ^> Attempting to build v_win.c with MSVC
-cl.exe /volatile:ms /Fo%ObjFile% /O2 /MD /D_VBOOTSTRAP vc\v_win.c user32.lib kernel32.lib advapi32.lib shell32.lib /link /nologo /out:v.exe /incremental:no
+cl.exe /volatile:ms /Fo%ObjFile% /W0 /MD /D_VBOOTSTRAP vc\v_win.c user32.lib kernel32.lib advapi32.lib shell32.lib /link /nologo /out:v.exe /incremental:no
 if %ERRORLEVEL% NEQ 0 (
     echo In some cases, compile errors happen because of the MSVC compiler version
     cl.exe
diff --git a/vlib/sokol/gfx/enums.v b/vlib/sokol/gfx/enums.v
index 575627b23c..c25f88fa6e 100644
--- a/vlib/sokol/gfx/enums.v
+++ b/vlib/sokol/gfx/enums.v
@@ -118,7 +118,7 @@ pub enum ImageType {
 	_num
 }
 
-pub enum CubeFace {
+pub enum CubeFace as u32 {
 	pos_x
 	neg_x
 	pos_y
diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 27d2881a5d..5f6eea6276 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -1164,6 +1164,7 @@ pub:
 	comments         []Comment   // comments before the first EnumField
 	fields           []EnumField // all the enum fields
 	attrs            []Attr      // attributes of enum declaration
+	typ              Type        // the default is `int`; can be changed by `enum Big as u64 { a = 5 }`
 	pos              token.Pos
 }
 
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index e8923e7d10..91d693693f 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1401,7 +1401,9 @@ pub fn (mut c Checker) const_decl(mut node ast.ConstDecl) {
 
 pub fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 	c.check_valid_pascal_case(node.name, 'enum name', node.pos)
-	mut seen := []i64{cap: node.fields.len}
+	mut useen := []u64{}
+	mut iseen := []i64{}
+	mut seen_enum_field_names := map[string]int{}
 	if node.fields.len == 0 {
 		c.error('enum cannot be empty', node.pos)
 	}
@@ -1410,35 +1412,114 @@ pub fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 		c.error('`builtin` module cannot have enums', node.pos)
 	}
 	*/
+	mut enum_imin := i64(0)
+	mut enum_imax := i64(0)
+	mut enum_umin := u64(0)
+	mut enum_umax := u64(0)
+	mut signed := true
+	senum_type := c.table.type_to_str(node.typ)
+	match node.typ {
+		ast.i8_type {
+			signed, enum_imin, enum_imax = true, -128, 0x7F
+		}
+		ast.i16_type {
+			signed, enum_imin, enum_imax = true, -32_768, 0x7FFF
+		}
+		ast.int_type {
+			signed, enum_imin, enum_imax = true, -2_147_483_648, 0x7FFF_FFFF
+		}
+		ast.i64_type {
+			signed, enum_imin, enum_imax = true, i64(-9223372036854775807 - 1), i64(0x7FFF_FFFF_FFFF_FFFF)
+		}
+		//
+		ast.u8_type {
+			signed, enum_umin, enum_umax = false, 0, 0xFF
+		}
+		ast.u16_type {
+			signed, enum_umin, enum_umax = false, 0, 0xFFFF
+		}
+		ast.u32_type {
+			signed, enum_umin, enum_umax = false, 0, 0xFFFF_FFFF
+		}
+		ast.u64_type {
+			signed, enum_umin, enum_umax = false, 0, 0xFFFF_FFFF_FFFF_FFFF
+		}
+		else {
+			c.error('`$senum_type` is not one of `i8`,`i16`,`int`,`i64`,`u8`,`u16`,`u32`,`u64`',
+				node.pos)
+		}
+	}
+	if enum_imin > 0 {
+		// ensure that the minimum value is negative, even with msvc, which has a bug that makes -2147483648 positive ...
+		enum_imin *= -1
+	}
 	for i, mut field in node.fields {
 		if !c.pref.experimental && util.contains_capital(field.name) {
 			// TODO C2V uses hundreds of enums with capitals, remove -experimental check once it's handled
 			c.error('field name `$field.name` cannot contain uppercase letters, use snake_case instead',
 				field.pos)
 		}
-		for j in 0 .. i {
-			if field.name == node.fields[j].name {
-				c.error('field name `$field.name` duplicate', field.pos)
-			}
+		if _ := seen_enum_field_names[field.name] {
+			c.error('duplicate enum field name `$field.name`', field.pos)
 		}
+		seen_enum_field_names[field.name] = i
 		if field.has_expr {
 			match mut field.expr {
 				ast.IntegerLiteral {
-					val := field.expr.val.i64()
-					if val < checker.int_min || val > checker.int_max {
-						c.error('enum value `$val` overflows int', field.expr.pos)
-					} else if !c.pref.translated && !c.file.is_translated && !node.is_multi_allowed
-						&& i64(val) in seen {
-						c.error('enum value `$val` already exists', field.expr.pos)
+					mut overflows := false
+					mut uval := u64(0)
+					mut ival := i64(0)
+					if signed {
+						val := field.expr.val.i64()
+						ival = val
+						if val < enum_imin || val >= enum_imax {
+							c.error('enum value `$field.expr.val` overflows the enum type `$senum_type`, values of which have to be in [$enum_imin, $enum_imax]',
+								field.expr.pos)
+							overflows = true
+						}
+					} else {
+						val := field.expr.val.u64()
+						uval = val
+						if val >= enum_umax {
+							c.error('enum value `$field.expr.val` overflows the enum type `$senum_type`, values of which have to be in [$enum_umin, $enum_umax]',
+								field.expr.pos)
+							overflows = true
+						}
+					}
+					if !overflows && !c.pref.translated && !c.file.is_translated
+						&& !node.is_multi_allowed {
+						if (signed && ival in iseen) || (!signed && uval in useen) {
+							c.error('enum value `$field.expr.val` already exists', field.expr.pos)
+						}
+					}
+					if signed {
+						iseen << ival
+					} else {
+						useen << uval
 					}
-					seen << i64(val)
 				}
-				ast.PrefixExpr {}
+				ast.PrefixExpr {
+					dump(field.expr)
+				}
 				ast.InfixExpr {
 					// Handle `enum Foo { x = 1 + 2 }`
 					c.infix_expr(mut field.expr)
 				}
-				// ast.ParExpr {} // TODO allow `.x = (1+2)`
+				ast.ParExpr {
+					c.expr(field.expr)
+				}
+				ast.CastExpr {
+					fe_type := c.cast_expr(mut field.expr)
+					if node.typ != fe_type {
+						sfe_type := c.table.type_to_str(fe_type)
+						c.error('the type of the enum value `$sfe_type` != the enum type itself `$senum_type`',
+							field.expr.pos)
+					}
+					if !fe_type.is_pure_int() {
+						c.error('the type of an enum value must be an integer type, like i8, u8, int, u64 etc.',
+							field.expr.pos)
+					}
+				}
 				else {
 					if mut field.expr is ast.Ident {
 						if field.expr.language == .c {
@@ -1449,21 +1530,38 @@ pub fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 					if pos.pos == 0 {
 						pos = field.pos
 					}
-					c.error('default value for enum has to be an integer', pos)
+					c.error('the default value for an enum has to be an integer', pos)
 				}
 			}
 		} else {
-			if seen.len > 0 {
-				last := seen[seen.len - 1]
-				if last == checker.int_max {
-					c.error('enum value overflows', field.pos)
-				} else if !c.pref.translated && !c.file.is_translated && !node.is_multi_allowed
-					&& last + 1 in seen {
-					c.error('enum value `${last + 1}` already exists', field.pos)
+			if signed {
+				if iseen.len > 0 {
+					ilast := iseen[iseen.len - 1]
+					if ilast == enum_imax {
+						c.error('enum value overflows type `$senum_type`, which has a maximum value of $enum_imax',
+							field.pos)
+					} else if !c.pref.translated && !c.file.is_translated && !node.is_multi_allowed
+						&& ilast + 1 in iseen {
+						c.error('enum value `${ilast + 1}` already exists', field.pos)
+					}
+					iseen << ilast + 1
+				} else {
+					iseen << 0
 				}
-				seen << last + 1
 			} else {
-				seen << 0
+				if useen.len > 0 {
+					ulast := useen[useen.len - 1]
+					if ulast == enum_umax {
+						c.error('enum value overflows type `$senum_type`, which has a maximum value of $enum_umax',
+							field.pos)
+					} else if !c.pref.translated && !c.file.is_translated && !node.is_multi_allowed
+						&& ulast + 1 in useen {
+						c.error('enum value `${ulast + 1}` already exists', field.pos)
+					}
+					useen << ulast + 1
+				} else {
+					useen << 0
+				}
 			}
 		}
 	}
@@ -2637,21 +2735,25 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 	if to_sym.kind == .enum_ {
 		if mut node.expr is ast.IntegerLiteral {
 			enum_typ_name := c.table.get_type_name(to_type)
-			node_val := node.expr.val.int()
+			node_val := node.expr.val.i64()
 
 			if enum_decl := c.table.enum_decls[to_sym.name] {
 				mut in_range := false
 				if enum_decl.is_flag {
 					// if a flag enum has 4 variants, the maximum possible value would have all 4 flags set (0b1111)
-					max_val := (1 << enum_decl.fields.len) - 1
-					in_range = node_val >= 0 && node_val <= max_val
+					max_val := (u64(1) << enum_decl.fields.len) - 1
+					in_range = node_val >= 0 && u64(node_val) <= max_val
 				} else {
-					mut enum_val := 0
+					mut enum_val := i64(0)
 
 					for enum_field in enum_decl.fields {
 						// check if the field of the enum value is an integer literal
 						if enum_field.expr is ast.IntegerLiteral {
-							enum_val = enum_field.expr.val.int()
+							enum_val = enum_field.expr.val.i64()
+						} else if comptime_value := c.eval_comptime_const_expr(enum_field.expr,
+							0)
+						{
+							enum_val = comptime_value.i64() or { -1 }
 						}
 						if node_val == enum_val {
 							in_range = true
diff --git a/vlib/v/checker/tests/enum_err.out b/vlib/v/checker/tests/enum_err.out
index 739305d3b9..669f2d25a1 100644
--- a/vlib/v/checker/tests/enum_err.out
+++ b/vlib/v/checker/tests/enum_err.out
@@ -1,5 +1,5 @@
-vlib/v/checker/tests/enum_err.vv:4:13: error: default value for enum has to be an integer
-    2 |
+vlib/v/checker/tests/enum_err.vv:4:13: error: the default value for an enum has to be an integer
+    2 | 
     3 | enum Color {
     4 |     green = 'green'
       |             ~~~~~~~
diff --git a/vlib/v/checker/tests/enum_field_name_duplicate_err.out b/vlib/v/checker/tests/enum_field_name_duplicate_err.out
index 6f1de8d93a..9f705a71c9 100644
--- a/vlib/v/checker/tests/enum_field_name_duplicate_err.out
+++ b/vlib/v/checker/tests/enum_field_name_duplicate_err.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/enum_field_name_duplicate_err.vv:5:2: error: field name `green` duplicate
+vlib/v/checker/tests/enum_field_name_duplicate_err.vv:5:2: error: duplicate enum field name `green`
     3 |     yellow
     4 |     blue
     5 |     green
diff --git a/vlib/v/checker/tests/enum_field_overflow.out b/vlib/v/checker/tests/enum_field_overflow.out
index 26f58437f4..c51d6580c4 100644
--- a/vlib/v/checker/tests/enum_field_overflow.out
+++ b/vlib/v/checker/tests/enum_field_overflow.out
@@ -1,6 +1,13 @@
-vlib/v/checker/tests/enum_field_overflow.vv:4:2: error: enum value overflows
+vlib/v/checker/tests/enum_field_overflow.vv:3:10: error: enum value `2147483647` overflows the enum type `int`, values of which have to be in [-2147483648, 2147483647]
+    1 | enum Color {
+    2 |     red
+    3 |     green = 2147483647
+      |             ~~~~~~~~~~
+    4 |     blue
+    5 | }
+vlib/v/checker/tests/enum_field_overflow.vv:4:2: error: enum value overflows type `int`, which has a maximum value of 2147483647
     2 |     red
     3 |     green = 2147483647
     4 |     blue
       |     ~~~~
-    5 | }
\ No newline at end of file
+    5 | }
diff --git a/vlib/v/checker/tests/enum_field_value_overflow.out b/vlib/v/checker/tests/enum_field_value_overflow.out
index c6bb9c0a10..a13678b4ec 100644
--- a/vlib/v/checker/tests/enum_field_value_overflow.out
+++ b/vlib/v/checker/tests/enum_field_value_overflow.out
@@ -1,7 +1,90 @@
-vlib/v/checker/tests/enum_field_value_overflow.vv:3:10: error: enum value `2147483648` overflows int
+vlib/v/checker/tests/enum_field_value_overflow.vv:3:10: error: enum value `2147483648` overflows the enum type `int`, values of which have to be in [-2147483648, 2147483647]
     1 | enum Color {
     2 |     red
     3 |     green = 2147483648
       |             ~~~~~~~~~~
     4 |     blue
-    5 | }
\ No newline at end of file
+    5 | }
+vlib/v/checker/tests/enum_field_value_overflow.vv:7:1: error: `string` is not one of `i8`,`i16`,`int`,`i64`,`u8`,`u16`,`u32`,`u64`
+    5 | }
+    6 | 
+    7 | enum ColorString as string {
+      | ~~~~~~~~~~~~~~~~
+    8 |     red
+    9 |     green = 'abc'
+vlib/v/checker/tests/enum_field_value_overflow.vv:9:10: error: the default value for an enum has to be an integer
+    7 | enum ColorString as string {
+    8 |     red
+    9 |     green = 'abc'
+      |             ~~~~~
+   10 |     blue
+   11 | }
+vlib/v/checker/tests/enum_field_value_overflow.vv:10:2: error: enum value overflows type `string`, which has a maximum value of 0
+    8 |     red
+    9 |     green = 'abc'
+   10 |     blue
+      |     ~~~~
+   11 | }
+   12 |
+vlib/v/checker/tests/enum_field_value_overflow.vv:15:10: error: enum value `128` overflows the enum type `i8`, values of which have to be in [-128, 127]
+   13 | enum ColorI8 as i8 {
+   14 |     red
+   15 |     green = 128
+      |             ~~~
+   16 |     blue
+   17 | }
+vlib/v/checker/tests/enum_field_value_overflow.vv:21:10: error: enum value `32769` overflows the enum type `i16`, values of which have to be in [-32768, 32767]
+   19 | enum ColorI16 as i16 {
+   20 |     red
+   21 |     green = 32769
+      |             ~~~~~
+   22 |     blue
+   23 | }
+vlib/v/checker/tests/enum_field_value_overflow.vv:27:10: error: enum value `2147483648` overflows the enum type `int`, values of which have to be in [-2147483648, 2147483647]
+   25 | enum ColorI32 {
+   26 |     red
+   27 |     green = 2147483648
+      |             ~~~~~~~~~~
+   28 |     blue
+   29 | }
+vlib/v/checker/tests/enum_field_value_overflow.vv:33:10: error: enum value `9223372036854775808` overflows the enum type `i64`, values of which have to be in [-9223372036854775808, 9223372036854775807]
+   31 | enum ColorI64 as i64 {
+   32 |     red
+   33 |     green = 9223372036854775808
+      |             ~~~~~~~~~~~~~~~~~~~
+   34 |     blue
+   35 | }
+vlib/v/checker/tests/enum_field_value_overflow.vv:34:2: error: enum value overflows type `i64`, which has a maximum value of 9223372036854775807
+   32 |     red
+   33 |     green = 9223372036854775808
+   34 |     blue
+      |     ~~~~
+   35 | }
+   36 |
+vlib/v/checker/tests/enum_field_value_overflow.vv:56:10: error: enum value `256` overflows the enum type `u8`, values of which have to be in [0, 255]
+   54 | // These should work however, since the type is unsigned:
+   55 | enum ColorU8ShouldFail as u8 {
+   56 |     green = 256
+      |             ~~~
+   57 | }
+   58 |
+vlib/v/checker/tests/enum_field_value_overflow.vv:60:10: error: enum value `65536` overflows the enum type `u16`, values of which have to be in [0, 65535]
+   58 | 
+   59 | enum ColorU16ShouldFail as u16 {
+   60 |     green = 65536
+      |             ~~~~~
+   61 | }
+   62 |
+vlib/v/checker/tests/enum_field_value_overflow.vv:64:10: error: enum value `4294967296` overflows the enum type `u32`, values of which have to be in [0, 4294967295]
+   62 | 
+   63 | enum ColorU32ShouldFail as u32 {
+   64 |     green = 4294967296
+      |             ~~~~~~~~~~
+   65 | }
+   66 |
+vlib/v/checker/tests/enum_field_value_overflow.vv:68:10: error: enum value `18446744073709551616` overflows the enum type `u64`, values of which have to be in [0, 18446744073709551615]
+   66 | 
+   67 | enum ColorU64ShouldFail as u64 {
+   68 |     green = 18446744073709551616
+      |             ~~~~~~~~~~~~~~~~~~~~
+   69 | }
diff --git a/vlib/v/checker/tests/enum_field_value_overflow.vv b/vlib/v/checker/tests/enum_field_value_overflow.vv
index cb9fb9af08..13802116c3 100644
--- a/vlib/v/checker/tests/enum_field_value_overflow.vv
+++ b/vlib/v/checker/tests/enum_field_value_overflow.vv
@@ -3,3 +3,67 @@ enum Color {
 	green = 2147483648
 	blue
 }
+
+enum ColorString as string {
+	red
+	green = 'abc'
+	blue
+}
+
+enum ColorI8 as i8 {
+	red
+	green = 128
+	blue
+}
+
+enum ColorI16 as i16 {
+	red
+	green = 32769
+	blue
+}
+
+enum ColorI32 {
+	red
+	green = 2147483648
+	blue
+}
+
+enum ColorI64 as i64 {
+	red
+	green = 9223372036854775808
+	blue
+}
+
+// These should work however, since the type is unsigned:
+enum ColorU8ShouldWork as u8 {
+	green = 128
+}
+
+enum ColorU16ShouldWork as u16 {
+	green = 32769
+}
+
+enum ColorU32ShouldWork as u32 {
+	green = 2147483648
+}
+
+enum ColorU64ShouldWork as u64 {
+	green = 9223372036854775808
+}
+
+// These should work however, since the type is unsigned:
+enum ColorU8ShouldFail as u8 {
+	green = 256
+}
+
+enum ColorU16ShouldFail as u16 {
+	green = 65536
+}
+
+enum ColorU32ShouldFail as u32 {
+	green = 4294967296
+}
+
+enum ColorU64ShouldFail as u64 {
+	green = 18446744073709551616
+}
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index b520739d5a..0f348ea53c 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -938,7 +938,11 @@ pub fn (mut f Fmt) enum_decl(node ast.EnumDecl) {
 	if node.is_pub {
 		f.write('pub ')
 	}
-	name := node.name.after('.')
+	mut name := node.name.after('.')
+	if node.typ != ast.int_type {
+		senum_type := f.table.type_to_str_using_aliases(node.typ, f.mod2alias)
+		name += ' as $senum_type'
+	}
 	if node.fields.len == 0 && node.pos.line_nr == node.pos.last_line {
 		f.writeln('enum $name {}\n')
 		return
diff --git a/vlib/v/gen/c/auto_str_methods.v b/vlib/v/gen/c/auto_str_methods.v
index b4230f3dcc..6353593a0e 100644
--- a/vlib/v/gen/c/auto_str_methods.v
+++ b/vlib/v/gen/c/auto_str_methods.v
@@ -306,8 +306,10 @@ fn (mut g Gen) gen_str_for_enum(info ast.Enum, styp string, str_fn_name string)
 		clean_name := util.strip_main_name(styp.replace('__', '.'))
 		g.auto_str_funcs.writeln('\tstring ret = _SLIT("$clean_name{");')
 		g.auto_str_funcs.writeln('\tint first = 1;')
+		g.auto_str_funcs.writeln('\tu64 zit = (u64)it;')
 		for i, val in info.vals {
-			g.auto_str_funcs.writeln('\tif (it & (1 << $i)) { if (!first) { ret = string__plus(ret, _SLIT(" | "));} ret = string__plus(ret, _SLIT(".$val")); first = 0;}')
+			mask := u64(1) << i
+			g.auto_str_funcs.writeln('\tif (zit & 0x${mask:016x}U) { if (!first) { ret = string__plus(ret, _SLIT(" | "));} ret = string__plus(ret, _SLIT(".$val")); first = 0;}')
 		}
 		g.auto_str_funcs.writeln('\tret = string__plus(ret, _SLIT("}"));')
 		g.auto_str_funcs.writeln('\treturn ret;')
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 93bb24934c..c69c2cbfea 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -3677,6 +3677,33 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 fn (mut g Gen) enum_decl(node ast.EnumDecl) {
 	enum_name := util.no_dots(node.name)
 	is_flag := node.is_flag
+	if g.pref.ccompiler == 'msvc' {
+		mut last_value := '0'
+		enum_typ_name := g.table.get_type_name(node.typ)
+		g.enum_typedefs.writeln('typedef $enum_typ_name $enum_name;')
+		for i, field in node.fields {
+			g.enum_typedefs.write_string('\t#define ${enum_name}__$field.name ')
+			g.enum_typedefs.write_string('(')
+			if is_flag {
+				g.enum_typedefs.write_string((u64(1) << i).str())
+				g.enum_typedefs.write_string('ULL')
+			} else if field.has_expr {
+				expr_str := g.expr_string(field.expr)
+				g.enum_typedefs.write_string(expr_str)
+				last_value = expr_str
+			} else {
+				if i != 0 {
+					last_value += '+1'
+				}
+				g.enum_typedefs.write_string(last_value)
+			}
+			g.enum_typedefs.writeln(')')
+		}
+		return
+	}
+	if node.typ != ast.int_type {
+		g.enum_typedefs.writeln('#pragma pack(push, 1)')
+	}
 	g.enum_typedefs.writeln('typedef enum {')
 	mut cur_enum_expr := ''
 	mut cur_enum_offset := 0
@@ -3690,8 +3717,9 @@ fn (mut g Gen) enum_decl(node ast.EnumDecl) {
 			cur_enum_offset = 0
 		} else if is_flag {
 			g.enum_typedefs.write_string(' = ')
-			cur_enum_expr = '1 << $i'
-			g.enum_typedefs.write_string((1 << i).str())
+			cur_enum_expr = 'u64(1) << $i'
+			g.enum_typedefs.write_string((u64(1) << i).str())
+			g.enum_typedefs.write_string('U')
 			cur_enum_offset = 0
 		}
 		cur_value := if cur_enum_offset > 0 {
@@ -3702,7 +3730,11 @@ fn (mut g Gen) enum_decl(node ast.EnumDecl) {
 		g.enum_typedefs.writeln(', // $cur_value')
 		cur_enum_offset++
 	}
-	g.enum_typedefs.writeln('} $enum_name;\n')
+	packed_attribute := if node.typ != ast.int_type { '__attribute__((packed))' } else { '' }
+	g.enum_typedefs.writeln('} $packed_attribute $enum_name;')
+	if node.typ != ast.int_type {
+		g.enum_typedefs.writeln('#pragma pack(pop)\n')
+	}
 }
 
 fn (mut g Gen) enum_expr(node ast.Expr) {
diff --git a/vlib/v/gen/native/tests/enum.vv b/vlib/v/gen/native/tests/enum.vv
index 642d1078a6..9e8292632c 100644
--- a/vlib/v/gen/native/tests/enum.vv
+++ b/vlib/v/gen/native/tests/enum.vv
@@ -31,7 +31,7 @@ fn match_test() {
 			assert false
 		}
 	}
-//	println(color)
+	//	println(color)
 	assert num == 3
 }
 
@@ -43,7 +43,7 @@ fn (_ Bar) baz() {}
 
 fn test_enum_variant_and_method_name_clash() {
 	x := Bar.baz
-//	println(x)
+	//	println(x)
 	x.baz()
 }
 
@@ -73,4 +73,5 @@ fn main() {
 	match_test()
 	test_enum_variant_and_method_name_clash()
 	value_test()
+	println('OK')
 }
diff --git a/vlib/v/gen/native/tests/enum.vv.out b/vlib/v/gen/native/tests/enum.vv.out
index e69de29bb2..d86bac9de5 100644
--- a/vlib/v/gen/native/tests/enum.vv.out
+++ b/vlib/v/gen/native/tests/enum.vv.out
@@ -0,0 +1 @@
+OK
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index a86eae1668..405b603904 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -3665,8 +3665,14 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		return ast.EnumDecl{}
 	}
 	name := p.prepend_mod(enum_name)
+	mut enum_type := ast.int_type
+	if p.tok.kind == .key_as {
+		p.next()
+		enum_type = p.parse_type()
+	}
 	p.check(.lcbr)
 	enum_decl_comments := p.eat_comments()
+	senum_type := p.table.get_type_name(enum_type)
 	mut vals := []string{}
 	// mut default_exprs := []ast.Expr{}
 	mut fields := []ast.EnumField{}
@@ -3698,8 +3704,8 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 	is_flag := p.attrs.contains('flag')
 	is_multi_allowed := p.attrs.contains('_allow_multiple_values')
 	if is_flag {
-		if fields.len > 32 {
-			p.error('when an enum is used as bit field, it must have a max of 32 fields')
+		if fields.len > 64 {
+			p.error('when an enum is used as bit field, it must have a max of 64 fields')
 			return ast.EnumDecl{}
 		}
 		for f in fields {
@@ -3712,12 +3718,12 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		pubfn := if p.mod == 'main' { 'fn' } else { 'pub fn' }
 		p.codegen('
 //
-[inline] $pubfn (    e &$enum_name) is_empty() bool           { return  int(*e) == 0 }
-[inline] $pubfn (    e &$enum_name) has(flag $enum_name) bool { return  (int(*e) &  (int(flag))) != 0 }
-[inline] $pubfn (    e &$enum_name) all(flag $enum_name) bool { return  (int(*e) &  (int(flag))) == int(flag) }
-[inline] $pubfn (mut e  $enum_name) set(flag $enum_name)      { unsafe{ *e = ${enum_name}(int(*e) |  (int(flag))) } }
-[inline] $pubfn (mut e  $enum_name) clear(flag $enum_name)    { unsafe{ *e = ${enum_name}(int(*e) & ~(int(flag))) } }
-[inline] $pubfn (mut e  $enum_name) toggle(flag $enum_name)   { unsafe{ *e = ${enum_name}(int(*e) ^  (int(flag))) } }
+[inline] $pubfn (    e &$enum_name) is_empty() bool           { return  ${senum_type}(*e) == 0 }
+[inline] $pubfn (    e &$enum_name) has(flag $enum_name) bool { return  (${senum_type}(*e) &  (${senum_type}(flag))) != 0 }
+[inline] $pubfn (    e &$enum_name) all(flag $enum_name) bool { return  (${senum_type}(*e) &  (${senum_type}(flag))) == ${senum_type}(flag) }
+[inline] $pubfn (mut e  $enum_name) set(flag $enum_name)      { unsafe{ *e = ${enum_name}(${senum_type}(*e) |  (${senum_type}(flag))) } }
+[inline] $pubfn (mut e  $enum_name) clear(flag $enum_name)    { unsafe{ *e = ${enum_name}(${senum_type}(*e) & ~(${senum_type}(flag))) } }
+[inline] $pubfn (mut e  $enum_name) toggle(flag $enum_name)   { unsafe{ *e = ${enum_name}(${senum_type}(*e) ^  (${senum_type}(flag))) } }
 //
 ')
 	}
@@ -3741,6 +3747,7 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 
 	enum_decl := ast.EnumDecl{
 		name: name
+		typ: enum_type
 		is_pub: is_pub
 		is_flag: is_flag
 		is_multi_allowed: is_multi_allowed
diff --git a/vlib/v/tests/enum_bitfield_64bit_test.v b/vlib/v/tests/enum_bitfield_64bit_test.v
new file mode 100644
index 0000000000..74c7106299
--- /dev/null
+++ b/vlib/v/tests/enum_bitfield_64bit_test.v
@@ -0,0 +1,124 @@
+// TODO: fix the formatting here, when VFMT ON/OFF is working
+
+[flag]
+enum PawnsBoard as u64 {
+	a8
+	b8
+	c8
+	d8
+	e8
+	f8
+	g8
+	h8
+	a7
+	b7
+	c7
+	d7
+	e7
+	f7
+	g7
+	h7
+	a6
+	b6
+	c6
+	d6
+	e6
+	f6
+	g6
+	h6
+	a5
+	b5
+	c5
+	d5
+	e5
+	f5
+	g5
+	h5
+	a4
+	b4
+	c4
+	d4
+	e4
+	f4
+	g4
+	h4
+	a3
+	b3
+	c3
+	d3
+	e3
+	f3
+	g3
+	h3
+	a2
+	b2
+	c2
+	d2
+	e2
+	f2
+	g2
+	h2
+	a1
+	b1
+	c1
+	d1
+	e1
+	f1
+	g1
+	h1
+}
+
+fn test_flag_enum_with_64_value_bits() {
+	last_value := PawnsBoard.h1
+	dump(u64(last_value))
+	assert u64(last_value) == 0x8000_0000_0000_0000
+
+	wb := PawnsBoard.a2 | .b2 | .c2 | .d2 | .e2 | .f2 | .g2 | .h2
+	dump(wb)
+	dump(u64(wb))
+	assert u64(wb) == 71776119061217280
+	assert '${u64(wb):064b}' == '0000000011111111000000000000000000000000000000000000000000000000'
+	assert '$wb' == 'PawnsBoard{.a2 | .b2 | .c2 | .d2 | .e2 | .f2 | .g2 | .h2}'
+
+	bb := PawnsBoard.a7 | .b7 | .c7 | .d7 | .e7 | .f7 | .g7 | .h7
+	dump(bb)
+	dump(u64(bb))
+	assert u64(bb) == 65280
+	assert '${u64(bb):064b}' == '0000000000000000000000000000000000000000000000001111111100000000'
+	assert '$bb' == 'PawnsBoard{.a7 | .b7 | .c7 | .d7 | .e7 | .f7 | .g7 | .h7}'
+
+	if false {
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.a1, .a2, .a3, .a4, .a5, .a6, .a7, .a8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.b1, .b2, .b3, .b4, .b5, .b6, .b7, .b8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.c1, .c2, .c3, .c4, .c5, .c6, .c7, .c8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.d1, .d2, .d3, .d4, .d5, .d6, .d7, .d8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.e1, .e2, .e3, .e4, .e5, .e6, .e7, .e8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.f1, .f2, .f3, .f4, .f5, .f6, .f7, .f8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.g1, .g2, .g3, .g4, .g5, .g6, .g7, .g8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+		eprintln('----------------------------------------------')
+		for x in [PawnsBoard.h1, .h2, .h3, .h4, .h5, .h6, .h7, .h8] {
+			eprintln('>> x: $x | hex value: ${u64(x).hex()}')
+		}
+	}
+}
diff --git a/vlib/v/tests/enum_explicit_size_big_and_small_test.v b/vlib/v/tests/enum_explicit_size_big_and_small_test.v
new file mode 100644
index 0000000000..e4ba5ded6e
--- /dev/null
+++ b/vlib/v/tests/enum_explicit_size_big_and_small_test.v
@@ -0,0 +1,83 @@
+enum SmallEnum as i8 {
+	a = -1
+	b = -4
+	c
+	d = 5
+	e
+}
+
+enum BigEnum as u64 {
+	a = 0xABCD_EF09_1234_5678
+	b = 0xFFFF_FFFF_FFFF_FFF0
+	c
+	d = 5
+	e
+}
+
+enum BigIEnum as i64 {
+	a = -999_999_999_999
+	b = -900_000_000_000
+	c
+	d = 900_000_000_000
+	e
+}
+
+fn test_small_enum() {
+	dump(sizeof(SmallEnum))
+	$if tinyc {
+		// TODO: TCC currently ignores `__attribute__((packed))` for enums, and uses an int instead, even with -fshort-enums :-|
+		assert sizeof(SmallEnum) == 4
+	} $else {
+		assert sizeof(SmallEnum) == 1
+	}
+	dump(i8(SmallEnum.a))
+	dump(i8(SmallEnum.b))
+	dump(i8(SmallEnum.c))
+	dump(i8(SmallEnum.d))
+	dump(i8(SmallEnum.e))
+	assert i8(SmallEnum.a) == -1
+	assert i8(SmallEnum.b) == -4
+	assert i8(SmallEnum.c) == -3
+	assert i8(SmallEnum.d) == 5
+	assert i8(SmallEnum.e) == 6
+}
+
+fn test_big_enum() {
+	assert sizeof(BigIEnum) == 8
+	assert BigEnum.a.str() == 'a'
+	assert BigEnum.b.str() == 'b'
+	assert BigEnum.c.str() == 'c'
+	assert BigEnum.d.str() == 'd'
+	assert BigEnum.e.str() == 'e'
+	dump(u64(BigEnum.a))
+	dump(u64(BigEnum.b))
+	dump(u64(BigEnum.c))
+	dump(u64(BigEnum.d))
+	dump(u64(BigEnum.e))
+	assert sizeof(BigEnum) == 8
+	assert u64(BigEnum.a) == 0xABCD_EF09_1234_5678
+	assert u64(BigEnum.b) == 0xFFFF_FFFF_FFFF_FFF0
+	assert u64(BigEnum.c) == 0xFFFF_FFFF_FFFF_FFF1
+	assert u64(BigEnum.d) == 5
+	assert u64(BigEnum.e) == 6
+}
+
+fn test_big_ienum() {
+	assert sizeof(BigIEnum) == 8
+	assert BigIEnum.a.str() == 'a'
+	assert BigIEnum.b.str() == 'b'
+	assert BigIEnum.c.str() == 'c'
+	assert BigIEnum.d.str() == 'd'
+	assert BigIEnum.e.str() == 'e'
+	dump(i64(BigIEnum.a))
+	dump(i64(BigIEnum.b))
+	dump(i64(BigIEnum.c))
+	dump(i64(BigIEnum.d))
+	dump(i64(BigIEnum.e))
+	assert sizeof(BigIEnum) == 8
+	assert i64(BigIEnum.a) == -999999999999
+	assert i64(BigIEnum.b) == -900000000000
+	assert i64(BigIEnum.c) == -899999999999
+	assert i64(BigIEnum.d) == 900000000000
+	assert i64(BigIEnum.e) == 900000000001
+}