parser,fmt,markused: add top level comptime $if support (enable $if platform { import module struct Abc {} }) (#25216)

vlib/v/ast/comptime_valid_idents.v

@@ -1,5 +1,7 @@
 module ast
 
+import v.pref
+
 pub const valid_comptime_if_os = ['windows', 'ios', 'macos', 'mach', 'darwin', 'hpux', 'gnu', 'qnx',
 	'linux', 'freebsd', 'openbsd', 'netbsd', 'bsd', 'dragonfly', 'android', 'termux', 'solaris',
 	'haiku', 'serenity', 'vinix', 'plan9', 'wasm32_emscripten']
@@ -22,3 +24,225 @@ fn all_valid_comptime_idents() []string {
 	res << valid_comptime_if_other
 	return res
 }
+
+pub fn eval_comptime_not_user_defined_ident(ident string, the_pref &pref.Preferences) !bool {
+	mut is_true := false
+	if ident in valid_comptime_if_os {
+		if ident_enum_val := pref.os_from_string(ident) {
+			if ident_enum_val == the_pref.os {
+				is_true = true
+			}
+		}
+	} else if ident in valid_comptime_if_compilers {
+		is_true = pref.cc_from_string(ident) == the_pref.ccompiler_type
+	} else if ident in valid_comptime_if_platforms {
+		match ident {
+			'amd64' {
+				is_true = the_pref.arch == .amd64
+			}
+			'i386' {
+				is_true = the_pref.arch == .i386
+			}
+			'aarch64' {
+				is_true = the_pref.arch == .arm64
+			}
+			'arm64' {
+				is_true = the_pref.arch == .arm64
+			}
+			'arm32' {
+				is_true = the_pref.arch == .arm32
+			}
+			'rv64' {
+				is_true = the_pref.arch == .rv64
+			}
+			'rv32' {
+				is_true = the_pref.arch == .rv32
+			}
+			's390x' {
+				is_true = the_pref.arch == .s390x
+			}
+			'ppc64le' {
+				is_true = the_pref.arch == .ppc64le
+			}
+			'loongarch64' {
+				is_true = the_pref.arch == .loongarch64
+			}
+			else {
+				return error('invalid \$if condition: unknown platforms `${ident}`')
+			}
+		}
+	} else if ident in valid_comptime_if_cpu_features {
+		match ident {
+			'x64' {
+				is_true = the_pref.m64
+			}
+			'x32' {
+				is_true = !the_pref.m64
+			}
+			'little_endian' {
+				is_true = $if little_endian { true } $else { false }
+			}
+			'big_endian' {
+				is_true = $if big_endian { true } $else { false }
+			}
+			else {
+				return error('invalid \$if condition: unknown cpu_features `${ident}`')
+			}
+		}
+	} else if ident in valid_comptime_if_other {
+		match ident {
+			'apk' {
+				is_true = the_pref.is_apk
+			}
+			'js' {
+				is_true = the_pref.backend.is_js()
+			}
+			'debug' {
+				is_true = the_pref.is_debug
+			}
+			'prod' {
+				is_true = the_pref.is_prod
+			}
+			'test' {
+				is_true = the_pref.is_test
+			}
+			'glibc' {
+				is_true = the_pref.is_glibc
+			}
+			'prealloc' {
+				is_true = the_pref.prealloc
+			}
+			'no_bounds_checking' {
+				is_true = the_pref.no_bounds_checking
+			}
+			'freestanding' {
+				is_true = the_pref.is_bare && !the_pref.output_cross_c
+			}
+			'threads' {
+				return error('threads should handle outside of `check_valid_ident()`')
+			}
+			'js_node' {
+				is_true = the_pref.backend == .js_node
+			}
+			'js_browser' {
+				is_true = the_pref.backend == .js_browser
+			}
+			'js_freestanding' {
+				is_true = the_pref.backend == .js_freestanding
+			}
+			'interpreter' {
+				is_true = the_pref.backend == .interpret
+			}
+			'es5' {
+				is_true = the_pref.output_es5
+			}
+			'profile' {
+				is_true = the_pref.is_prof
+			}
+			'wasm32' {
+				is_true = the_pref.arch == .wasm32
+			}
+			'wasm32_wasi' {
+				is_true = the_pref.os == .wasm32_wasi
+			}
+			'fast_math' {
+				is_true = the_pref.fast_math
+			}
+			'native' {
+				is_true = the_pref.backend == .native
+			}
+			'autofree' {
+				is_true = the_pref.autofree
+			}
+			else {
+				return error('invalid \$if condition: unknown other indent `${ident}`')
+			}
+		}
+	} else if ident in the_pref.compile_defines {
+		is_true = true
+	} else {
+		return error('invalid \$if condition: unknown indent `${ident}`')
+	}
+	return is_true
+}
+
+pub const system_ident_map = {
+	// OS
+	'windows':            '_WIN32'
+	'ios':                '__TARGET_IOS__'
+	'macos':              '__APPLE__'
+	'mach':               '__MACH__'
+	'darwin':             '__DARWIN__'
+	'hpux':               '__HPUX__'
+	'gnu':                '__GNU__'
+	'qnx':                '__QNX__'
+	'linux':              '__linux__'
+	'serenity':           '__serenity__'
+	'plan9':              '__plan9__'
+	'vinix':              '__vinix__'
+	'freebsd':            '__FreeBSD__'
+	'openbsd':            '__OpenBSD__'
+	'netbsd':             '__NetBSD__'
+	'bsd':                '__BSD__'
+	'dragonfly':          '__DragonFly__'
+	'android':            '__ANDROID__'
+	'termux':             '__TERMUX__'
+	'solaris':            '__sun'
+	'haiku':              '__HAIKU__'
+	// Backend
+	'js':                 '_VJS'
+	'wasm32_emscripten':  '__EMSCRIPTEN__'
+	'native':             '_VNATIVE'
+	// Compiler
+	'gcc':                '__V_GCC__'
+	'tinyc':              '__TINYC__'
+	'clang':              '__clang__'
+	'mingw':              '__MINGW32__'
+	'msvc':               '_MSC_VER'
+	'cplusplus':          '__cplusplus'
+	// Others
+	'threads':            '__VTHREADS__'
+	'gcboehm':            '_VGCBOEHM'
+	'debug':              '_VDEBUG'
+	'prod':               '_VPROD'
+	'profile':            '_VPROFILE'
+	'test':               '_VTEST'
+	'glibc':              '__GLIBC__'
+	'prealloc':           '_VPREALLOC'
+	'no_bounds_checking': 'CUSTOM_DEFINE_no_bounds_checking'
+	'freestanding':       '_VFREESTANDING'
+	'autofree':           '_VAUTOFREE'
+	// CPU
+	'amd64':              '__V_amd64'
+	'aarch64':            '__V_arm64'
+	'arm64':              '__V_arm64' // aarch64 alias
+	'arm32':              '__V_arm32'
+	'i386':               '__V_x86'
+	'rv64':               '__V_rv64'
+	'riscv64':            '__V_rv64' // rv64 alias
+	'rv32':               '__V_rv32'
+	'riscv32':            '__V_rv32' // rv32 alias
+	's390x':              '__V_s390x'
+	'ppc64le':            '__V_ppc64le'
+	'loongarch64':        '__V_loongarch64'
+	'x64':                'TARGET_IS_64BIT'
+	'x32':                'TARGET_IS_32BIT'
+	'little_endian':      'TARGET_ORDER_IS_LITTLE'
+	'big_endian':         'TARGET_ORDER_IS_BIG'
+}
+
+pub fn comptime_if_to_ifdef(name string, the_pref &pref.Preferences) !string {
+	if name == 'fast_math' {
+		return if the_pref.ccompiler_type == .msvc {
+			// turned on by: `-cflags /fp:fast`
+			'_M_FP_FAST'
+		} else {
+			// turned on by: `-cflags -ffast-math`
+			'__FAST_MATH__'
+		}
+	}
+	if ifdef := system_ident_map[name] {
+		return ifdef
+	}
+	return error('bad os ifdef name `${name}`')
+}

vlib/v/checker/comptime.v

@@ -784,191 +784,6 @@ fn (mut c Checker) evaluate_once_comptime_if_attribute(mut node ast.Attr) bool {
 	return node.ct_skip
 }
 
-fn (mut c Checker) comptime_if_to_ifdef(name string) !string {
-	match name {
-		// platforms/os-es:
-		'windows' {
-			return '_WIN32'
-		}
-		'ios' {
-			return '__TARGET_IOS__'
-		}
-		'macos' {
-			return '__APPLE__'
-		}
-		'mach' {
-			return '__MACH__'
-		}
-		'darwin' {
-			return '__DARWIN__'
-		}
-		'hpux' {
-			return '__HPUX__'
-		}
-		'gnu' {
-			return '__GNU__'
-		}
-		'qnx' {
-			return '__QNX__'
-		}
-		'linux' {
-			return '__linux__'
-		}
-		'serenity' {
-			return '__serenity__'
-		}
-		'plan9' {
-			return '__plan9__'
-		}
-		'vinix' {
-			return '__vinix__'
-		}
-		'freebsd' {
-			return '__FreeBSD__'
-		}
-		'openbsd' {
-			return '__OpenBSD__'
-		}
-		'netbsd' {
-			return '__NetBSD__'
-		}
-		'bsd' {
-			return '__BSD__'
-		}
-		'dragonfly' {
-			return '__DragonFly__'
-		}
-		'android' {
-			return '__ANDROID__'
-		}
-		'termux' {
-			// Note: termux is running on Android natively so __ANDROID__ will also be defined
-			return '__TERMUX__'
-		}
-		'solaris' {
-			return '__sun'
-		}
-		'haiku' {
-			return '__HAIKU__'
-		}
-		//
-		'js' {
-			return '_VJS'
-		}
-		'wasm32_emscripten' {
-			return '__EMSCRIPTEN__'
-		}
-		'native' {
-			return '_VNATIVE' // when using the native backend, cgen is inactive
-		}
-		// compilers:
-		'gcc' {
-			return '__V_GCC__'
-		}
-		'tinyc' {
-			return '__TINYC__'
-		}
-		'clang' {
-			return '__clang__'
-		}
-		'mingw' {
-			return '__MINGW32__'
-		}
-		'msvc' {
-			return '_MSC_VER'
-		}
-		'cplusplus' {
-			return '__cplusplus'
-		}
-		// other:
-		'threads' {
-			return '__VTHREADS__'
-		}
-		'gcboehm' {
-			return '_VGCBOEHM'
-		}
-		'debug' {
-			return '_VDEBUG'
-		}
-		'prod' {
-			return '_VPROD'
-		}
-		'profile' {
-			return '_VPROFILE'
-		}
-		'test' {
-			return '_VTEST'
-		}
-		'glibc' {
-			return '__GLIBC__'
-		}
-		'prealloc' {
-			return '_VPREALLOC'
-		}
-		'no_bounds_checking' {
-			return 'CUSTOM_DEFINE_no_bounds_checking'
-		}
-		'freestanding' {
-			return '_VFREESTANDING'
-		}
-		'autofree' {
-			return '_VAUTOFREE'
-		}
-		// architectures:
-		'amd64' {
-			return '__V_amd64'
-		}
-		'aarch64', 'arm64' {
-			return '__V_arm64'
-		}
-		'arm32' {
-			return '__V_arm32'
-		}
-		'i386' {
-			return '__V_x86'
-		}
-		'rv64', 'riscv64' {
-			return '__V_rv64'
-		}
-		'rv32', 'riscv32' {
-			return '__V_rv32'
-		}
-		's390x' {
-			return '__V_s390x'
-		}
-		'ppc64le' {
-			return '__V_ppc64le'
-		}
-		'loongarch64' {
-			return '__V_loongarch64'
-		}
-		// bitness:
-		'x64' {
-			return 'TARGET_IS_64BIT'
-		}
-		'x32' {
-			return 'TARGET_IS_32BIT'
-		}
-		// endianness:
-		'little_endian' {
-			return 'TARGET_ORDER_IS_LITTLE'
-		}
-		'big_endian' {
-			return 'TARGET_ORDER_IS_BIG'
-		}
-		'fast_math' {
-			if c.pref.ccompiler_type == .msvc {
-				// turned on by: `-cflags /fp:fast`
-				return '_M_FP_FAST'
-			}
-			// turned on by: `-cflags -ffast-math`
-			return '__FAST_MATH__'
-		}
-		else {}
-	}
-	return error('bad os ifdef name "${name}"')
-}
-
 // check if `ident` is a function generic, such as `T`
 fn (mut c Checker) is_generic_ident(ident string) bool {
 	if !isnil(c.table.cur_fn) && ident in c.table.cur_fn.generic_names
@@ -1141,10 +956,6 @@ fn (mut c Checker) comptime_if_cond(mut cond ast.Expr, mut sb strings.Builder) (
 			should_record_ident = true
 			is_user_ident = true
 			ident_name = cname
-			// ifdef := c.comptime_if_to_ifdef(cname, true) or {
-			//	c.error(err.msg(), cond.pos)
-			//	return false, false
-			//}
 			sb.write_string('defined(CUSTOM_DEFINE_${cname})')
 			is_true = cname in c.pref.compile_defines
 			return is_true, false
@@ -1483,143 +1294,12 @@ fn (mut c Checker) comptime_if_cond(mut cond ast.Expr, mut sb strings.Builder) (
 			should_record_ident = true
 			is_user_ident = false
 			ident_name = cname
-			if cname in ast.valid_comptime_if_os {
-				if cname_enum_val := pref.os_from_string(cname) {
-					if cname_enum_val == c.pref.os {
-						is_true = true
-					}
-				}
-			} else if cname in ast.valid_comptime_if_compilers {
-				is_true = pref.cc_from_string(cname) == c.pref.ccompiler_type
-			} else if cname in ast.valid_comptime_if_platforms {
-				if cname == 'aarch64' {
-					c.note('use `arm64` instead of `aarch64`', cond.pos)
-				}
-				match cname {
-					'amd64' {
-						is_true = c.pref.arch == .amd64
-					}
-					'i386' {
-						is_true = c.pref.arch == .i386
-					}
-					'aarch64' {
-						is_true = c.pref.arch == .arm64
-					}
-					'arm64' {
-						is_true = c.pref.arch == .arm64
-					}
-					'arm32' {
-						is_true = c.pref.arch == .arm32
-					}
-					'rv64' {
-						is_true = c.pref.arch == .rv64
-					}
-					'rv32' {
-						is_true = c.pref.arch == .rv32
-					}
-					's390x' {
-						is_true = c.pref.arch == .s390x
-					}
-					'ppc64le' {
-						is_true = c.pref.arch == .ppc64le
-					}
-					'loongarch64' {
-						is_true = c.pref.arch == .loongarch64
-					}
-					else {
-						c.error('invalid \$if condition: unknown platforms `${cname}`',
-							cond.pos)
-						return false, false
-					}
-				}
-			} else if cname in ast.valid_comptime_if_cpu_features {
-				match cname {
-					'x64' {
-						is_true = c.pref.m64
-					}
-					'x32' {
-						is_true = !c.pref.m64
-					}
-					'little_endian' {
-						is_true = $if little_endian { true } $else { false }
-					}
-					'big_endian' {
-						is_true = $if big_endian { true } $else { false }
-					}
-					else {
-						c.error('invalid \$if condition: unknown cpu_features `${cname}`',
-							cond.pos)
-						return false, false
-					}
-				}
-			} else if cname in ast.valid_comptime_if_other {
-				match cname {
-					'apk' {
-						is_true = c.pref.is_apk
-					}
-					'js' {
-						is_true = c.pref.backend.is_js()
-					}
-					'debug' {
-						is_true = c.pref.is_debug
-					}
-					'prod' {
-						is_true = c.pref.is_prod
-					}
-					'test' {
-						is_true = c.pref.is_test
-					}
-					'glibc' {
-						is_true = c.pref.is_glibc
-					}
-					'prealloc' {
-						is_true = c.pref.prealloc
-					}
-					'no_bounds_checking' {
-						is_true = c.pref.no_bounds_checking
-					}
-					'freestanding' {
-						is_true = c.pref.is_bare && !c.pref.output_cross_c
-					}
-					'threads' {
+			if cname in ast.valid_comptime_not_user_defined {
+				if cname == 'threads' {
 					is_true = c.table.gostmts > 0
-					}
-					'js_node' {
-						is_true = c.pref.backend == .js_node
-					}
-					'js_browser' {
-						is_true = c.pref.backend == .js_browser
-					}
-					'js_freestanding' {
-						is_true = c.pref.backend == .js_freestanding
-					}
-					'interpreter' {
-						is_true = c.pref.backend == .interpret
-					}
-					'es5' {
-						is_true = c.pref.output_es5
-					}
-					'profile' {
-						is_true = c.pref.is_prof
-					}
-					'wasm32' {
-						is_true = c.pref.arch == .wasm32
-					}
-					'wasm32_wasi' {
-						is_true = c.pref.os == .wasm32_wasi
-					}
-					'fast_math' {
-						is_true = c.pref.fast_math
-					}
-					'native' {
-						is_true = c.pref.backend == .native
-					}
-					'autofree' {
-						is_true = c.pref.autofree
-					}
-					else {
-						c.error('invalid \$if condition: unknown other indent `${cname}`',
-							cond.pos)
+				} else {
+					is_true = ast.eval_comptime_not_user_defined_ident(cname, c.pref) or {
+						c.error(err.msg(), cond.pos)
 						return false, false
 					}
 				}
@@ -1655,7 +1335,7 @@ fn (mut c Checker) comptime_if_cond(mut cond ast.Expr, mut sb strings.Builder) (
 				c.error('invalid \$if condition: unknown indent `${cname}`', cond.pos)
 				return false, false
 			}
-			if ifdef := c.comptime_if_to_ifdef(cname) {
+			if ifdef := ast.comptime_if_to_ifdef(cname, c.pref) {
 				sb.write_string('defined(${ifdef})')
 			} else {
 				sb.write_string('${is_true}')

vlib/v/fmt/fmt.v

@@ -51,6 +51,8 @@ pub mut:
 	wsinfix_depth            int
 	format_state             FormatState
 	source_text              string // can be set by `echo "println('hi')" | v fmt`, i.e. when processing source not from a file, but from stdin. In this case, it will contain the entire input text. You can use f.file.path otherwise, and read from that file.
+	global_processed_imports []string
+	branch_processed_imports []string
 }
 
 @[params]
@@ -317,12 +319,17 @@ pub fn (mut f Fmt) import_stmt(imp ast.Import) {
 		return
 	}
 	imp_stmt := f.imp_stmt_str(imp)
-	if imp_stmt in f.processed_imports {
+	if imp_stmt in f.global_processed_imports
+		|| (f.inside_comptime_if && imp_stmt in f.branch_processed_imports) {
 		// Skip duplicates.
 		f.import_comments(imp.next_comments)
 		return
 	}
-	f.processed_imports << imp_stmt
+	if f.inside_comptime_if {
+		f.branch_processed_imports << imp_stmt
+	} else {
+		f.global_processed_imports << imp_stmt
+	}
 	if !f.format_state.is_vfmt_on {
 		original_imp_line := f.get_source_lines()#[imp.pos.line_nr..imp.pos.last_line + 1].join('\n')
 		// Same line comments(`imp.comments`) are included in the `original_imp_line`.
@@ -1070,7 +1077,7 @@ pub fn (mut f Fmt) enum_decl(node ast.EnumDecl) {
 		f.writeln('')
 		f.comments(field.next_comments, has_nl: true, level: .indent)
 	}
-	f.writeln('}\n')
+	f.writeln('}')
 }
 
 pub fn (mut f Fmt) fn_decl(node ast.FnDecl) {
@@ -2354,6 +2361,7 @@ pub fn (mut f Fmt) if_expr(node ast.IfExpr) {
 	start_len := f.line_len
 	for {
 		for i, branch in node.branches {
+			f.branch_processed_imports.clear()
 			mut sum_len := 0
 			if i > 0 {
 				// `else`, close previous branch

vlib/v/fmt/tests/comptime_if_top_enum_empty_line_keep.vv

@@ -0,0 +1,16 @@
+$if new_c_1 ? {
+	pub enum Enum1 {
+		enum1_a
+		enum1_b
+	}
+} $else $if new_c_2 ? {
+	pub enum Enum1 {
+		enum1_c
+		enum1_d
+	}
+} $else {
+	pub enum Enum1 {
+		enum1_e
+		enum1_f
+	}
+}

vlib/v/fmt/tests/enums_expected.vv

@@ -2,7 +2,6 @@ pub enum PubEnum {
 	foo
 	bar
 }
-
 enum PrivateEnum {
 	foo
 	bar

vlib/v/markused/markused.v

@@ -331,18 +331,8 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 	}
 }
 
-fn all_global_decl(ast_files []&ast.File) (map[string]ast.FnDecl, map[string]ast.ConstField, map[string]ast.GlobalField, map[string]ast.TypeDecl, map[string]ast.StructDecl) {
-	util.timing_start(@METHOD)
-	defer {
-		util.timing_measure(@METHOD)
-	}
-	mut all_fns := map[string]ast.FnDecl{}
-	mut all_consts := map[string]ast.ConstField{}
-	mut all_globals := map[string]ast.GlobalField{}
-	mut all_decltypes := map[string]ast.TypeDecl{}
-	mut all_structs := map[string]ast.StructDecl{}
-	for i in 0 .. ast_files.len {
-		for node in ast_files[i].stmts {
+fn all_global_decl_in_stmts(stmts []ast.Stmt, mut all_fns map[string]ast.FnDecl, mut all_consts map[string]ast.ConstField, mut all_globals map[string]ast.GlobalField, mut all_decltypes map[string]ast.TypeDecl, mut all_structs map[string]ast.StructDecl) {
+	for node in stmts {
 		match node {
 			ast.FnDecl {
 				fkey := node.fkey()
@@ -370,9 +360,49 @@ fn all_global_decl(ast_files []&ast.File) (map[string]ast.FnDecl, map[string]ast
 					all_decltypes[node.name] = node
 				}
 			}
+			ast.ExprStmt {
+				match node.expr {
+					ast.IfExpr {
+						if node.expr.is_comptime {
+							// top level comptime $if
+							for branch in node.expr.branches {
+								all_global_decl_in_stmts(branch.stmts, mut all_fns, mut
+									all_consts, mut all_globals, mut all_decltypes, mut
+									all_structs)
+							}
+						}
+					}
+					ast.MatchExpr {
+						if node.expr.is_comptime {
+							// top level comptime $match
+							for branch in node.expr.branches {
+								all_global_decl_in_stmts(branch.stmts, mut all_fns, mut
+									all_consts, mut all_globals, mut all_decltypes, mut
+									all_structs)
+							}
+						}
+					}
 					else {}
 				}
 			}
+			else {}
+		}
+	}
+}
+
+fn all_global_decl(ast_files []&ast.File) (map[string]ast.FnDecl, map[string]ast.ConstField, map[string]ast.GlobalField, map[string]ast.TypeDecl, map[string]ast.StructDecl) {
+	util.timing_start(@METHOD)
+	defer {
+		util.timing_measure(@METHOD)
+	}
+	mut all_fns := map[string]ast.FnDecl{}
+	mut all_consts := map[string]ast.ConstField{}
+	mut all_globals := map[string]ast.GlobalField{}
+	mut all_decltypes := map[string]ast.TypeDecl{}
+	mut all_structs := map[string]ast.StructDecl{}
+	for i in 0 .. ast_files.len {
+		all_global_decl_in_stmts(ast_files[i].stmts, mut all_fns, mut all_consts, mut
+			all_globals, mut all_decltypes, mut all_structs)
 	}
 	return all_fns, all_consts, all_globals, all_decltypes, all_structs
 }

vlib/v/parser/enum.v

@@ -96,7 +96,10 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		// p.warn('enum val $val')
 		if p.tok.kind == .assign {
 			p.next()
+			old_assign_rhs := p.inside_assign_rhs
+			p.inside_assign_rhs = true
 			expr = p.expr(0)
+			p.inside_assign_rhs = old_assign_rhs
 			has_expr = true
 			uses_exprs = true
 		}
@@ -225,7 +228,8 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		is_pub: is_pub
 	})
 
-	if idx in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx] {
+	if idx in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx]
+		&& !p.pref.is_fmt {
 		p.error_with_pos('cannot register enum `${name}`, another type with this name exists',
 			end_pos)
 	}

vlib/v/parser/fn.v

@@ -359,6 +359,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			check_name = if language == .js { p.check_js_name() } else { p.check_name() }
 			name = check_name
 		}
+
 		if language == .v && !p.pref.translated && !p.is_translated && !p.builtin_mod
 			&& util.contains_capital(check_name) {
 			p.error_with_pos('function names cannot contain uppercase letters, use snake_case instead',
@@ -655,6 +656,7 @@ run them via `v file.v` instead',
 	})
 	*/
 	// Body
+	keep_fn_name := p.cur_fn_name
 	p.cur_fn_name = name
 	mut stmts := []ast.Stmt{}
 	body_start_pos := p.tok.pos()
@@ -671,6 +673,7 @@ run them via `v file.v` instead',
 		p.inside_unsafe_fn = false
 		p.inside_fn = false
 	}
+	p.cur_fn_name = keep_fn_name
 	if !no_body && are_params_type_only {
 		p.error_with_pos('functions with type only params can not have bodies', body_start_pos)
 		return ast.FnDecl{

vlib/v/parser/if_match.v

@@ -5,6 +5,7 @@ module parser
 
 import v.ast
 import v.token
+import v.pkgconfig
 
 fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 	was_inside_if_expr := p.inside_if_expr
@@ -25,6 +26,8 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 	mut has_else := false
 	mut comments := []ast.Comment{}
 	mut prev_guard := false
+	mut comptime_skip_curr_stmts := false
+	mut comptime_has_true_branch := false
 	for p.tok.kind in [.key_if, .key_else] {
 		p.inside_if = true
 		if is_comptime {
@@ -58,6 +61,16 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 						is_special:   true
 					})
 				}
+				if is_comptime && comptime_has_true_branch && !p.pref.is_fmt
+					&& !p.pref.output_cross_c {
+					p.skip_scope()
+					branches << ast.IfBranch{
+						pos:      start_pos.extend(end_pos)
+						body_pos: body_pos.extend(p.tok.pos())
+						comments: comments
+						scope:    p.scope
+					}
+				} else {
 					branches << ast.IfBranch{
 						stmts:    p.parse_block_no_scope(false)
 						pos:      start_pos.extend(end_pos)
@@ -65,6 +78,7 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 						comments: comments
 						scope:    p.scope
 					}
+				}
 				p.close_scope()
 				comments = []
 				break
@@ -114,7 +128,10 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 			comments << p.eat_comments()
 			p.check(.decl_assign)
 			comments << p.eat_comments()
+			old_assign_rhs := p.inside_assign_rhs
+			p.inside_assign_rhs = true
 			expr := p.expr(0)
+			p.inside_assign_rhs = old_assign_rhs
 			if expr !in [ast.CallExpr, ast.IndexExpr, ast.PrefixExpr, ast.SelectorExpr, ast.Ident] {
 				p.error_with_pos('if guard condition expression is illegal, it should return an Option',
 					expr.pos())
@@ -141,6 +158,12 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 			p.comptime_if_cond = true
 			p.inside_if_cond = true
 			cond = p.expr(0)
+			if is_comptime && p.is_in_top_level_comptime(p.inside_assign_rhs) {
+				comptime_skip_curr_stmts = !p.comptime_if_cond(mut cond)
+				if !comptime_skip_curr_stmts {
+					comptime_has_true_branch = true
+				}
+			}
 			if mut cond is ast.InfixExpr && !is_comptime {
 				if cond.op in [.key_is, .not_is] {
 					if mut cond.left is ast.Ident {
@@ -170,6 +193,16 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 			return ast.IfExpr{}
 		}
 		p.open_scope()
+		if is_comptime && comptime_skip_curr_stmts && !p.pref.is_fmt && !p.pref.output_cross_c {
+			p.skip_scope()
+			branches << ast.IfBranch{
+				cond:     cond
+				pos:      start_pos.extend(end_pos)
+				body_pos: body_pos.extend(p.prev_tok.pos())
+				comments: comments
+				scope:    p.scope
+			}
+		} else {
 			stmts := p.parse_block_no_scope(false)
 			branches << ast.IfBranch{
 				cond:     cond
@@ -179,6 +212,7 @@ fn (mut p Parser) if_expr(is_comptime bool, is_expr bool) ast.IfExpr {
 				comments: comments
 				scope:    p.scope
 			}
+		}
 		p.close_scope()
 		if is_guard {
 			p.close_scope()
@@ -570,3 +604,167 @@ fn (mut p Parser) select_expr() ast.SelectExpr {
 		has_exception: has_else || has_timeout
 	}
 }
+
+fn (mut p Parser) comptime_if_cond(mut cond ast.Expr) bool {
+	mut is_true := false
+	match mut cond {
+		ast.BoolLiteral {
+			return cond.val
+		}
+		ast.ParExpr {
+			return p.comptime_if_cond(mut cond.expr)
+		}
+		ast.PrefixExpr {
+			if cond.op != .not {
+				p.error('invalid \$if prefix operator, only allow `!`.')
+				return false
+			}
+			return !p.comptime_if_cond(mut cond.right)
+		}
+		ast.PostfixExpr {
+			if cond.op != .question {
+				p.error('invalid \$if postfix operator, only allow `?`.')
+				return false
+			}
+			if cond.expr !is ast.Ident {
+				p.error('invalid \$if postfix condition, only allow `Indent`.')
+				return false
+			}
+			cname := (cond.expr as ast.Ident).name
+			return cname in p.pref.compile_defines
+		}
+		ast.InfixExpr {
+			match cond.op {
+				.and, .logical_or {
+					l := p.comptime_if_cond(mut cond.left)
+					r := p.comptime_if_cond(mut cond.right)
+					// if at least one of the cond has `keep_stmts`, we should keep stmts
+					return if cond.op == .and { l && r } else { l || r }
+				}
+				.eq, .ne, .gt, .lt, .ge, .le {
+					match mut cond.left {
+						ast.Ident {
+							// $if version == 2
+							match mut cond.right {
+								ast.StringLiteral {
+									match cond.op {
+										.eq {
+											is_true = cond.left.str() == cond.right.str()
+										}
+										.ne {
+											is_true = cond.left.str() != cond.right.str()
+										}
+										else {
+											p.error('string type only support `==` and `!=` operator')
+											return false
+										}
+									}
+								}
+								ast.IntegerLiteral {
+									match cond.op {
+										.eq {
+											is_true = cond.left.str().i64() == cond.right.val.i64()
+										}
+										.ne {
+											is_true = cond.left.str().i64() != cond.right.val.i64()
+										}
+										.gt {
+											is_true = cond.left.str().i64() > cond.right.val.i64()
+										}
+										.lt {
+											is_true = cond.left.str().i64() < cond.right.val.i64()
+										}
+										.ge {
+											is_true = cond.left.str().i64() >= cond.right.val.i64()
+										}
+										.le {
+											is_true = cond.left.str().i64() <= cond.right.val.i64()
+										}
+										else {
+											p.error('int type only support `==` `!=` `>` `<` `>=` and `<=` operator')
+											return false
+										}
+									}
+								}
+								ast.BoolLiteral {
+									match cond.op {
+										.eq {
+											is_true = cond.left.str().bool() == cond.right.val
+										}
+										.ne {
+											is_true = cond.left.str().bool() != cond.right.val
+										}
+										else {
+											p.error('bool type only support `==` and `!=` operator')
+											return false
+										}
+									}
+								}
+								else {
+									p.error('compare only support string int and bool type')
+									return false
+								}
+							}
+							return is_true
+						}
+						else {
+							p.error('invalid \$if condition')
+							return false
+						}
+					}
+					p.error('invalid \$if condition')
+					return false
+				}
+				else {
+					p.error('invalid \$if operator: ${cond.op}')
+					return false
+				}
+			}
+		}
+		ast.Ident {
+			cname := cond.name
+			if cname in ast.valid_comptime_not_user_defined {
+				if cname == 'threads' {
+					is_true = p.table.gostmts > 0
+				} else {
+					is_true = ast.eval_comptime_not_user_defined_ident(cname, p.pref) or {
+						p.error(err.msg())
+						return false
+					}
+				}
+			} else {
+				p.error('invalid \$if condition: unknown indent `${cname}`')
+				return false
+			}
+			return is_true
+		}
+		ast.ComptimeCall {
+			if cond.kind == .pkgconfig {
+				if mut m := pkgconfig.main([cond.args_var]) {
+					if _ := m.run() {
+						is_true = true
+					} else {
+						// pkgconfig not found, do not issue error, just set false
+						is_true = false
+					}
+				} else {
+					p.error(err.msg())
+					is_true = false
+				}
+				return is_true
+			}
+			if cond.kind == .d {
+				is_true = cond.compile_value.bool()
+				return is_true
+			}
+			p.error('invalid \$if condition: unknown ComptimeCall')
+			return false
+		}
+		else {
+			p.error('invalid \$if condition ${cond}')
+			return false
+		}
+	}
+
+	return is_true
+}

vlib/v/parser/parser.v

@@ -111,6 +111,7 @@ mut:
 	generic_type_level       int  // to avoid infinite recursion segfaults due to compiler bugs in ensure_type_exists
 	main_already_defined     bool // TODO move to checker
 	is_vls                   bool
+	inside_import_section    bool
 pub mut:
 	scanner &scanner.Scanner = unsafe { nil }
 	table   &ast.Table       = unsafe { nil }
@@ -290,6 +291,7 @@ pub fn (mut p Parser) parse() &ast.File {
 	} else {
 		stmts << module_decl
 	}
+	p.inside_import_section = true
 	// imports
 	for {
 		if p.tok.kind == .key_import {
@@ -451,6 +453,12 @@ fn (mut p Parser) parse_block() []ast.Stmt {
 	return stmts
 }
 
+fn (mut p Parser) is_in_top_level_comptime(inside_assign_rhs bool) bool {
+	// TODO: find out a better way detect we are in top level.
+	return p.cur_fn_name.len == 0 && p.inside_ct_if_expr && !inside_assign_rhs && !p.script_mode
+		&& p.tok.kind != .name
+}
+
 fn (mut p Parser) parse_block_no_scope(is_top_level bool) []ast.Stmt {
 	p.check(.lcbr)
 	mut stmts := []ast.Stmt{cap: 20}
@@ -459,7 +467,12 @@ fn (mut p Parser) parse_block_no_scope(is_top_level bool) []ast.Stmt {
 	if p.tok.kind != .rcbr {
 		mut count := 0
 		for p.tok.kind !in [.eof, .rcbr] {
+			if p.is_in_top_level_comptime(old_assign_rhs) {
+				// top level `$if cond { println() }` should goto `p.stmt()`
+				stmts << p.top_stmt()
+			} else {
 				stmts << p.stmt(is_top_level)
+			}
 			count++
 			if count % 100000 == 0 {
 				if p.is_vls {
@@ -617,6 +630,10 @@ fn (p &Parser) trace_parser(label string) {
 fn (mut p Parser) top_stmt() ast.Stmt {
 	p.trace_parser('top_stmt')
 	for {
+		if p.tok.kind !in [.key_import, .comment, .dollar] {
+			// import section should only prepend by `import`, `comment` or `$if`.
+			p.inside_import_section = false
+		}
 		match p.tok.kind {
 			.key_pub {
 				match p.peek_tok.kind {
@@ -660,8 +677,10 @@ fn (mut p Parser) top_stmt() ast.Stmt {
 				return p.interface_decl()
 			}
 			.key_import {
+				if !p.inside_import_section {
 					p.error_with_pos('`import x` can only be declared at the beginning of the file',
 						p.tok.pos())
+				}
 				return p.import_stmt()
 			}
 			.key_global {
@@ -677,13 +696,15 @@ fn (mut p Parser) top_stmt() ast.Stmt {
 				return p.struct_decl(false)
 			}
 			.dollar {
-				if p.peek_tok.kind == .eof {
+				match p.peek_tok.kind {
+					.eof {
 						return p.unexpected(got: 'eof')
 					}
-				if p.peek_tok.kind == .key_for {
+					.key_for {
 						comptime_for_stmt := p.comptime_for()
 						return p.other_stmts(comptime_for_stmt)
-				} else if p.peek_tok.kind == .key_if {
+					}
+					.key_if {
 						if_expr := p.if_expr(true, false)
 						cur_stmt := ast.ExprStmt{
 							expr: if_expr
@@ -694,10 +715,35 @@ fn (mut p Parser) top_stmt() ast.Stmt {
 						} else {
 							return p.other_stmts(cur_stmt)
 						}
+					}
+					.key_match {
+						mut pos := p.tok.pos()
+						expr := p.match_expr(true)
+						pos.update_last_line(p.prev_tok.line_nr)
+						return ast.ExprStmt{
+							expr: expr
+							pos:  pos
+						}
+					}
+					.name {
+						// handles $dbg directly without registering token
+						if p.peek_tok.lit == 'dbg' {
+							return p.dbg_stmt()
 						} else {
+							mut pos := p.tok.pos()
+							expr := p.expr(0)
+							pos.update_last_line(p.prev_tok.line_nr)
+							return ast.ExprStmt{
+								expr: expr
+								pos:  pos
+							}
+						}
+					}
+					else {
 						return p.unexpected()
 					}
 				}
+			}
 			.hash {
 				return p.hash()
 			}
@@ -2470,7 +2516,10 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 		}
 		mut expr := ast.Expr{}
 		if !is_virtual_c_const {
+			old_inside_assign_rhs := p.inside_assign_rhs
+			p.inside_assign_rhs = true
 			expr = p.expr(0)
+			p.inside_assign_rhs = old_inside_assign_rhs
 		}
 		if is_block {
 			end_comments << p.eat_comments(same_line: true)
@@ -2596,7 +2645,10 @@ fn (mut p Parser) global_decl() ast.GlobalDecl {
 		mut typ_pos := token.Pos{}
 		if has_expr {
 			p.next() // =
+			old_assign_rhs := p.inside_assign_rhs
+			p.inside_assign_rhs = true
 			expr = p.expr(0)
+			p.inside_assign_rhs = old_assign_rhs
 			match mut expr {
 				ast.CastExpr, ast.StructInit, ast.ArrayInit, ast.ChanInit {
 					typ = expr.typ
@@ -2759,7 +2811,8 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 			}
 			is_pub: is_pub
 		})
-		if typ in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx] {
+		if typ in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx]
+			&& !p.pref.is_fmt {
 			p.error_with_pos('cannot register sum type `${name}`, another type with this name exists',
 				name_pos)
 			return ast.SumTypeDecl{}
@@ -2806,7 +2859,8 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		is_pub:     is_pub
 	})
 	type_end_pos := p.prev_tok.pos()
-	if idx in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx] {
+	if idx in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx]
+		&& !p.pref.is_fmt {
 		p.error_with_pos('cannot register alias `${name}`, another type with this name exists',
 			name_pos)
 		return ast.AliasTypeDecl{}
@@ -3017,3 +3071,23 @@ fn (mut p Parser) add_defer_var(ident ast.Ident) {
 		}
 	}
 }
+
+// skip `{...}`
+fn (mut p Parser) skip_scope() {
+	mut br_cnt := 0
+	for {
+		match p.tok.kind {
+			.lcbr { br_cnt++ }
+			.rcbr { br_cnt-- }
+			.eof { break }
+			else {}
+		}
+		if br_cnt == 0 {
+			break
+		}
+		p.next()
+	}
+	if p.tok.kind == .rcbr {
+		p.next()
+	}
+}

vlib/v/parser/struct.v

@@ -338,7 +338,10 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 				if p.tok.kind == .assign {
 					// Default value
 					p.next()
+					old_assign_rhs := p.inside_assign_rhs
+					p.inside_assign_rhs = true
 					default_expr = p.expr(0)
+					p.inside_assign_rhs = old_assign_rhs
 					match mut default_expr {
 						ast.EnumVal { default_expr.typ = typ }
 						// TODO: implement all types??
@@ -457,7 +460,7 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 		}
 	}
 	// allow duplicate c struct declarations
-	if ret == -1 && language != .c {
+	if ret == -1 && language != .c && !p.pref.is_fmt {
 		p.error_with_pos('cannot register struct `${name}`, another type with this name exists',
 			name_pos)
 		return ast.StructDecl{}
@@ -671,7 +674,7 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 		}
 		language: language
 	)
-	if reg_idx == -1 {
+	if reg_idx == -1 && !p.pref.is_fmt {
 		p.error_with_pos('cannot register interface `${interface_name}`, another type with this name exists',
 			name_pos)
 		return ast.InterfaceDecl{}

vlib/v/tests/comptime/comptime_if_top_1_test.v

@@ -0,0 +1,94 @@
+// vtest vflags: -d new_1 -d new_a_1 -d new_b_1 -d new_c_1 -d new_d_1 -d new_e_1
+module main
+
+// this is comment, should skip
+
+$if new_1 ? {
+	// this is comment, should skip
+	import os
+	// this is comment, should skip
+} $else $if new_2 ? {
+	// this is comment, should skip
+	import math
+	// this is comment, should skip
+} $else {
+	// this is comment, should skip
+	import time
+	// this is comment, should skip
+}
+// this is comment, should skip
+
+const t = $if amd64 { 1 } $else { 2 }
+
+$if new_a_1 ? {
+	pub type Digits = u64
+} $else $if new_a_2 ? {
+	pub type Digits = u32
+} $else {
+	pub type Digits = u8
+}
+
+$if new_b_1 ? {
+	pub const const1 = '123'
+} $else $if new_b_2 ? {
+	pub const const1 = 123
+} $else {
+	pub const const1 = 1.1
+}
+
+$if new_c_1 ? {
+	pub enum Enum1 {
+		enum1_a
+		enum1_b
+	}
+} $else $if new_c_2 ? {
+	pub enum Enum1 {
+		enum1_c
+		enum1_d
+	}
+} $else {
+	pub enum Enum1 {
+		enum1_e
+		enum1_f
+	}
+}
+
+$if new_d_1 ? {
+	pub struct Struct1 {
+		a int
+	}
+} $else $if new_d_2 ? {
+	pub struct Struct1 {
+		b int
+	}
+} $else {
+	pub struct Struct1 {
+		c int
+	}
+}
+
+$if new_e_1 ? {
+	pub fn ret() string {
+		return 'new_e_1'
+	}
+} $else $if new_e_2 ? {
+	pub fn ret() string {
+		return 'new_e_2'
+	}
+} $else {
+	pub fn ret() string {
+		return 'new_e_3'
+	}
+}
+
+fn test_main() {
+	assert os.user_os().len > 0
+	assert t in [1, 2]
+	assert sizeof(Digits) == 8 // Digits == u64
+	assert const1 == '123'
+	_ := Enum1.enum1_a // should compile
+	_ := Struct1{
+		a: 123
+	} // should compile
+	assert ret() == 'new_e_1'
+}

vlib/v/tests/comptime/comptime_if_top_2_test.v

@@ -0,0 +1,94 @@
+// vtest vflags: -d new_2 -d new_a_2 -d new_b_2 -d new_c_2 -d new_d_2 -d new_e_2
+module main
+
+// this is comment, should skip
+
+$if new_1 ? {
+	// this is comment, should skip
+	import os
+	// this is comment, should skip
+} $else $if new_2 ? {
+	// this is comment, should skip
+	import math
+	// this is comment, should skip
+} $else {
+	// this is comment, should skip
+	import time
+	// this is comment, should skip
+}
+// this is comment, should skip
+
+const t = $if amd64 { 1 } $else { 2 }
+
+$if new_a_1 ? {
+	pub type Digits = u64
+} $else $if new_a_2 ? {
+	pub type Digits = u32
+} $else {
+	pub type Digits = u8
+}
+
+$if new_b_1 ? {
+	pub const const1 = '123'
+} $else $if new_b_2 ? {
+	pub const const1 = 123
+} $else {
+	pub const const1 = 1.1
+}
+
+$if new_c_1 ? {
+	pub enum Enum1 {
+		enum1_a
+		enum1_b
+	}
+} $else $if new_c_2 ? {
+	pub enum Enum1 {
+		enum1_c
+		enum1_d
+	}
+} $else {
+	pub enum Enum1 {
+		enum1_e
+		enum1_f
+	}
+}
+
+$if new_d_1 ? {
+	pub struct Struct1 {
+		a int
+	}
+} $else $if new_d_2 ? {
+	pub struct Struct1 {
+		b int
+	}
+} $else {
+	pub struct Struct1 {
+		c int
+	}
+}
+
+$if new_e_1 ? {
+	pub fn ret() string {
+		return 'new_e_1'
+	}
+} $else $if new_e_2 ? {
+	pub fn ret() string {
+		return 'new_e_2'
+	}
+} $else {
+	pub fn ret() string {
+		return 'new_e_3'
+	}
+}
+
+fn test_main() {
+	assert math.max(1, 2) == 2
+	assert t in [1, 2]
+	assert sizeof(Digits) == 4 // Digits == u32
+	assert const1 == 123
+	_ := Enum1.enum1_d // should compile
+	_ := Struct1{
+		b: 123
+	} // should compile
+	assert ret() == 'new_e_2'
+}

vlib/v/tests/comptime/comptime_if_top_3_test.v

@@ -0,0 +1,94 @@
+// vtest vflags: -d new_3 -d new_a_3 -d new_b_3 -d new_c_3 -d new_d_3 -d new_e_3
+module main
+
+// this is comment, should skip
+
+$if new_1 ? {
+	// this is comment, should skip
+	import os
+	// this is comment, should skip
+} $else $if new_2 ? {
+	// this is comment, should skip
+	import math
+	// this is comment, should skip
+} $else {
+	// this is comment, should skip
+	import time
+	// this is comment, should skip
+}
+// this is comment, should skip
+
+const t = $if amd64 { 1 } $else { 2 }
+
+$if new_a_1 ? {
+	pub type Digits = u64
+} $else $if new_a_2 ? {
+	pub type Digits = u32
+} $else {
+	pub type Digits = u8
+}
+
+$if new_b_1 ? {
+	pub const const1 = '123'
+} $else $if new_b_2 ? {
+	pub const const1 = 123
+} $else {
+	pub const const1 = 1.1
+}
+
+$if new_c_1 ? {
+	pub enum Enum1 {
+		enum1_a
+		enum1_b
+	}
+} $else $if new_c_2 ? {
+	pub enum Enum1 {
+		enum1_c
+		enum1_d
+	}
+} $else {
+	pub enum Enum1 {
+		enum1_e
+		enum1_f
+	}
+}
+
+$if new_d_1 ? {
+	pub struct Struct1 {
+		a int
+	}
+} $else $if new_d_2 ? {
+	pub struct Struct1 {
+		b int
+	}
+} $else {
+	pub struct Struct1 {
+		c int
+	}
+}
+
+$if new_e_1 ? {
+	pub fn ret() string {
+		return 'new_e_1'
+	}
+} $else $if new_e_2 ? {
+	pub fn ret() string {
+		return 'new_e_2'
+	}
+} $else {
+	pub fn ret() string {
+		return 'new_e_3'
+	}
+}
+
+fn test_main() {
+	assert time.days_in_year == 365
+	assert t in [1, 2]
+	assert sizeof(Digits) == 1 // Digits == u8
+	assert const1 == 1.1
+	_ := Enum1.enum1_e // should compile
+	_ := Struct1{
+		c: 123
+	} // should compile
+	assert ret() == 'new_e_3'
+}