all: support `[noreturn] fn abc() { for{} }`, mark panic/1 and exit/1with it too. (#10654)

doc/docs.md

@@ -4763,6 +4763,21 @@ fn legacy_function() {}
 fn inlined_function() {
 }
 
+// This function's calls will NOT be inlined.
+[noinline]
+fn function() {
+}
+
+// This function will NOT return to its callers.
+// Such functions can be used at the end of or blocks,
+// just like exit/1 or panic/1. Such functions can not
+// have return types, and should end either in for{}, or
+// by calling other `[noreturn]` functions.
+[noreturn]
+fn forever() {
+	for {}
+}
+
 // The following struct must be allocated on the heap. Therefore, it can only be used as a
 // reference (`&Window`) or inside another reference (`&OuterStruct{ Window{...} }`).
 [heap]

vlib/builtin/builtin.c.v

@@ -4,9 +4,16 @@ type FnExitCb = fn ()
 
 fn C.atexit(f FnExitCb) int
 
+[noreturn]
+fn vhalt() {
+	for {}
+}
+
 // exit terminates execution immediately and returns exit `code` to the shell.
+[noreturn]
 pub fn exit(code int) {
 	C.exit(code)
+	vhalt()
 }
 
 fn vcommithash() string {
@@ -17,6 +24,7 @@ fn vcommithash() string {
 // recent versions of tcc print nicer backtraces automatically
 // NB: the duplication here is because tcc_backtrace should be called directly
 // inside the panic functions.
+[noreturn]
 fn panic_debug(line_no int, file string, mod string, fn_name string, s string) {
 	// NB: the order here is important for a stabler test output
 	// module is less likely to change than function, etc...
@@ -52,14 +60,17 @@ fn panic_debug(line_no int, file string, mod string, fn_name string, s string) {
 			C.exit(1)
 		}
 	}
+	vhalt()
 }
 
+[noreturn]
 pub fn panic_optional_not_set(s string) {
 	panic('optional not set ($s)')
 }
 
 // panic prints a nice error message, then exits the process with exit code of 1.
 // It also shows a backtrace on most platforms.
+[noreturn]
 pub fn panic(s string) {
 	$if freestanding {
 		bare_panic(s)
@@ -87,6 +98,7 @@ pub fn panic(s string) {
 			C.exit(1)
 		}
 	}
+	vhalt()
 }
 
 // eprintln prints a message with a line end, to stderr. Both stderr and stdout are flushed.

vlib/builtin/linux_bare/libc_impl.v

@@ -140,6 +140,7 @@ pub fn write(fd i64, buf &byte, count u64) i64 {
 	return x
 }
 
+[noreturn]
 fn bare_panic(msg string) {
 	println('V panic' + msg)
 	exit(1)
@@ -150,6 +151,7 @@ fn bare_backtrace() string {
 }
 
 [export: 'exit']
+[noreturn]
 fn __exit(code int) {
 	sys_exit(code)
 }

vlib/builtin/linux_bare/linux_syscalls.v

@@ -303,8 +303,10 @@ fn sys_execve(filename &byte, argv []&byte, envp []&byte) int {
 }
 
 // 60 sys_exit
+[noreturn]
 fn sys_exit(ec int) {
 	sys_call1(60, u64(ec))
+	for {}
 }
 
 // 102 sys_getuid

vlib/v/ast/ast.v

@@ -363,6 +363,7 @@ pub:
 	is_pub          bool
 	is_variadic     bool
 	is_anon         bool
+	is_noreturn     bool           // true, when [noreturn] is used on a fn
 	is_manualfree   bool           // true, when [manualfree] is used on a fn
 	is_main         bool           // true for `fn main()`
 	is_test         bool           // true for `fn test_abcde`
@@ -421,6 +422,7 @@ pub mut:
 	is_method          bool
 	is_field           bool // temp hack, remove ASAP when re-impl CallExpr / Selector (joe)
 	is_keep_alive      bool // GC must not free arguments before fn returns
+	is_noreturn        bool // whether the function/method is marked as [noreturn]
 	args               []CallArg
 	expected_arg_types []Type
 	language           Language

vlib/v/ast/table.v

@@ -73,6 +73,7 @@ pub:
 	generic_names   []string
 	is_pub          bool
 	is_deprecated   bool // `[deprecated] fn abc(){}`
+	is_noreturn     bool // `[noreturn] fn abc(){}`
 	is_unsafe       bool // `[unsafe] fn abc(){}`
 	is_placeholder  bool
 	is_main         bool // `fn main(){}`

vlib/v/checker/checker.v

@@ -1936,6 +1936,7 @@ pub fn (mut c Checker) method_call(mut call_expr ast.CallExpr) ast.Type {
 		}
 	}
 	if has_method {
+		call_expr.is_noreturn = method.is_noreturn
 		if !method.is_pub && !c.pref.is_test && method.mod != c.mod {
 			// If a private method is called outside of the module
 			// its receiver type is defined in, show an error.
@@ -2439,10 +2440,13 @@ pub fn (mut c Checker) fn_call(mut call_expr ast.CallExpr) ast.Type {
 			c.table.fns[fn_name].usages++
 		}
 	}
+	mut is_native_builtin := false
 	if !found && c.pref.backend == .native {
 		if fn_name in native.builtins {
 			c.table.fns[fn_name].usages++
-			return ast.void_type
+			found = true
+			func = c.table.fns[fn_name]
+			is_native_builtin = true
 		}
 	}
 	if !found && c.pref.is_vsh {
@@ -2457,6 +2461,9 @@ pub fn (mut c Checker) fn_call(mut call_expr ast.CallExpr) ast.Type {
 			c.table.fns[os_name].usages++
 		}
 	}
+	if is_native_builtin {
+		return ast.void_type
+	}
 	// check for arg (var) of fn type
 	if !found {
 		if v := call_expr.scope.find_var(fn_name) {
@@ -2493,6 +2500,7 @@ pub fn (mut c Checker) fn_call(mut call_expr ast.CallExpr) ast.Type {
 		c.error('unknown function: $fn_name', call_expr.pos)
 		return ast.void_type
 	}
+	call_expr.is_noreturn = func.is_noreturn
 	if !found_in_args {
 		if _ := call_expr.scope.find_var(fn_name) {
 			c.error('ambiguous call to: `$fn_name`, may refer to fn `$fn_name` or variable `$fn_name`',
@@ -2906,13 +2914,13 @@ pub fn (mut c Checker) check_or_expr(or_expr ast.OrExpr, ret_type ast.Type, expr
 				c.expected_or_type = ast.void_type
 				type_fits := c.check_types(last_stmt_typ, ret_type)
 					&& last_stmt_typ.nr_muls() == ret_type.nr_muls()
-				is_panic_or_exit := is_expr_panic_or_exit(last_stmt.expr)
+				is_noreturn := is_noreturn_callexpr(last_stmt.expr)
-				if type_fits || is_panic_or_exit {
+				if type_fits || is_noreturn {
 					return
 				}
 				expected_type_name := c.table.type_to_str(ret_type.clear_flag(.optional))
 				if last_stmt.typ == ast.void_type {
-					c.error('`or` block must provide a default value of type `$expected_type_name`, or return/exit/continue/break/panic',
+					c.error('`or` block must provide a default value of type `$expected_type_name`, or return/continue/break or call a [noreturn] function like panic(err) or exit(1)',
 						last_stmt.pos)
 				} else {
 					type_name := c.table.type_to_str(last_stmt_typ)
@@ -2942,7 +2950,7 @@ pub fn (mut c Checker) check_or_expr(or_expr ast.OrExpr, ret_type ast.Type, expr
 				if last_stmt.typ == ast.void_type {
 					return
 				}
-				if is_expr_panic_or_exit(last_stmt.expr) {
+				if is_noreturn_callexpr(last_stmt.expr) {
 					return
 				}
 				if c.check_types(last_stmt.typ, expr_return_type) {
@@ -2959,11 +2967,11 @@ pub fn (mut c Checker) check_or_expr(or_expr ast.OrExpr, ret_type ast.Type, expr
 	}
 }
 
-fn is_expr_panic_or_exit(expr ast.Expr) bool {
+fn is_noreturn_callexpr(expr ast.Expr) bool {
-	match expr {
+	if expr is ast.CallExpr {
-		ast.CallExpr { return !expr.is_method && expr.name in ['panic', 'exit'] }
+		return expr.is_noreturn
-		else { return false }
 	}
+	return false
 }
 
 pub fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
@@ -7572,9 +7580,11 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 	}
 	c.fn_scope = node.scope
 	c.stmts(node.stmts)
-	node.has_return = c.returns || has_top_return(node.stmts)
+	node_has_top_return := has_top_return(node.stmts)
+	node.has_return = c.returns || node_has_top_return
+	c.check_noreturn_fn_decl(mut node)
 	if node.language == .v && !node.no_body && node.return_type != ast.void_type && !node.has_return
-		&& (node.is_method || node.name !in ['panic', 'exit']) {
+		&& !node.is_noreturn {
 		if c.inside_anon_fn {
 			c.error('missing return at the end of an anonymous function', node.pos)
 		} else if !node.attrs.contains('_naked') {
@@ -7594,21 +7604,28 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 	node.source_file = c.file
 }
 
+// NB: has_top_return/1 should be called on *already checked* stmts,
+// which do have their stmt.expr.is_noreturn set properly:
 fn has_top_return(stmts []ast.Stmt) bool {
 	for stmt in stmts {
-		if stmt is ast.Return {
+		match stmt {
+			ast.Return {
 				return true
-		} else if stmt is ast.Block {
+			}
+			ast.Block {
 				if has_top_return(stmt.stmts) {
 					return true
 				}
-		} else if stmt is ast.ExprStmt {
+			}
+			ast.ExprStmt {
 				if stmt.expr is ast.CallExpr {
-				if !stmt.expr.is_method && stmt.expr.name in ['panic', 'exit'] {
+					if stmt.expr.is_noreturn {
 						return true
 					}
 				}
 			}
+			else {}
+		}
 	}
 	return false
 }

vlib/v/checker/noreturn.v

@@ -0,0 +1,112 @@
+module checker
+
+import v.ast
+
+fn (mut c Checker) check_noreturn_fn_decl(mut node ast.FnDecl) {
+	if !node.is_noreturn {
+		return
+	}
+	if node.no_body {
+		return
+	}
+	if uses_return_stmt(node.stmts) {
+		c.error('[noreturn] functions cannot use return statements', node.pos)
+	}
+	if node.return_type != ast.void_type {
+		c.error('[noreturn] functions cannot have return types', node.pos)
+	} else {
+		if node.stmts.len != 0 {
+			mut is_valid_end_of_noreturn_fn := false
+			last_stmt := node.stmts.last()
+			match last_stmt {
+				ast.ExprStmt {
+					if last_stmt.expr is ast.CallExpr {
+						if last_stmt.expr.should_be_skipped {
+							c.error('[noreturn] functions cannot end with a skippable `[if ..]` call',
+								last_stmt.pos)
+						}
+						if last_stmt.expr.is_noreturn {
+							is_valid_end_of_noreturn_fn = true
+						}
+					}
+				}
+				ast.ForStmt {
+					if last_stmt.is_inf && last_stmt.stmts.len == 0 {
+						is_valid_end_of_noreturn_fn = true
+					}
+				}
+				else {}
+			}
+			if !is_valid_end_of_noreturn_fn {
+				c.error('[noreturn] functions should end with a call to another [noreturn] function, or with an infinite `for {}` loop',
+					last_stmt.pos)
+			}
+		}
+	}
+}
+
+fn uses_return_stmt(stmts []ast.Stmt) bool {
+	if stmts.len == 0 {
+		return false
+	}
+	for stmt in stmts {
+		match stmt {
+			ast.Return {
+				return true
+			}
+			ast.Block {
+				if uses_return_stmt(stmt.stmts) {
+					return true
+				}
+			}
+			ast.ExprStmt {
+				match stmt.expr {
+					ast.CallExpr {
+						if uses_return_stmt(stmt.expr.or_block.stmts) {
+							return true
+						}
+					}
+					ast.MatchExpr {
+						for b in stmt.expr.branches {
+							if uses_return_stmt(b.stmts) {
+								return true
+							}
+						}
+					}
+					ast.SelectExpr {
+						for b in stmt.expr.branches {
+							if uses_return_stmt(b.stmts) {
+								return true
+							}
+						}
+					}
+					ast.IfExpr {
+						for b in stmt.expr.branches {
+							if uses_return_stmt(b.stmts) {
+								return true
+							}
+						}
+					}
+					else {}
+				}
+			}
+			ast.ForStmt {
+				if uses_return_stmt(stmt.stmts) {
+					return true
+				}
+			}
+			ast.ForCStmt {
+				if uses_return_stmt(stmt.stmts) {
+					return true
+				}
+			}
+			ast.ForInStmt {
+				if uses_return_stmt(stmt.stmts) {
+					return true
+				}
+			}
+			else {}
+		}
+	}
+	return false
+}

vlib/v/checker/tests/noreturn_with_non_empty_loop_at_end.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/noreturn_with_non_empty_loop_at_end.vv:4:6: error: [noreturn] functions should end with a call to another [noreturn] function, or with an infinite `for {}` loop
+    2 | fn another() {
+    3 |     eprintln(@FN)
+    4 |     for {
+      |         ^
+    5 |         break
+    6 |     }

vlib/v/checker/tests/noreturn_with_non_empty_loop_at_end.vv

@@ -0,0 +1,19 @@
+[noreturn]
+fn another() {
+	eprintln(@FN)
+	for {
+		break
+	}
+}
+
+[noreturn]
+fn abc() {
+	eprintln(@FN)
+	another()
+}
+
+fn main() {
+	eprintln('start')
+	abc()
+	eprintln('done')
+}

vlib/v/checker/tests/noreturn_with_return.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/noreturn_with_return.vv:2:1: error: [noreturn] functions cannot use return statements
+    1 | [noreturn]
+    2 | fn another() {
+      | ~~~~~~~~~~~~
+    3 |     eprintln(@FN)
+    4 |     // for{}
+vlib/v/checker/tests/noreturn_with_return.vv:6:2: error: [noreturn] functions should end with a call to another [noreturn] function, or with an infinite `for {}` loop
+    4 |     // for{}
+    5 |     // exit(0)
+    6 |     return
+      |     ~~~~~~
+    7 | }
+    8 |

vlib/v/checker/tests/noreturn_with_return.vv

@@ -0,0 +1,19 @@
+[noreturn]
+fn another() {
+	eprintln(@FN)
+	// for{}
+	// exit(0)
+	return
+}
+
+[noreturn]
+fn abc() {
+	eprintln(@FN)
+	another()
+}
+
+fn main() {
+	eprintln('start')
+	abc()
+	eprintln('done')
+}

vlib/v/checker/tests/noreturn_without_loop_or_another_noreturn_at_end.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/noreturn_without_loop_or_another_noreturn_at_end.vv:3:2: error: [noreturn] functions should end with a call to another [noreturn] function, or with an infinite `for {}` loop
+    1 | [noreturn]
+    2 | fn another() {
+    3 |     eprintln(@FN)
+      |     ~~~~~~~~~~~~~
+    4 | }
+    5 |

vlib/v/checker/tests/noreturn_without_loop_or_another_noreturn_at_end.vv

@@ -0,0 +1,16 @@
+[noreturn]
+fn another() {
+	eprintln(@FN)
+}
+
+[noreturn]
+fn abc() {
+	eprintln(@FN)
+	another()
+}
+
+fn main() {
+	eprintln('start')
+	abc()
+	eprintln('done')
+}

vlib/v/checker/tests/run/noreturn_fn_can_be_used_instead_of_panic.run.out

@@ -0,0 +1 @@
+log_and_die: error: oh no

vlib/v/checker/tests/run/noreturn_fn_can_be_used_instead_of_panic.vv

@@ -0,0 +1,14 @@
+fn abc() ?int {
+	return error('oh no')
+}
+
+[noreturn]
+fn log_and_die(e IError) {
+	eprintln('${@FN}: error: $e')
+	exit(77)
+}
+
+fn main() {
+	x := abc() or { log_and_die(err) }
+	println(x)
+}

vlib/v/gen/c/cgen.v

@@ -5164,10 +5164,12 @@ fn (mut g Gen) assoc(node ast.Assoc) {
 	}
 }
 
+[noreturn]
 fn verror(s string) {
 	util.verror('cgen error', s)
 }
 
+[noreturn]
 fn (g &Gen) error(s string, pos token.Position) {
 	ferror := util.formatted_error('cgen error:', s, g.file.path, pos)
 	eprintln(ferror)

vlib/v/gen/c/cheaders.v

@@ -165,11 +165,26 @@ const c_common_macros = '
 	#define _MOV
 #endif
 
-#if defined(__TINYC__) && defined(__has_include)
 // tcc does not support has_include properly yet, turn it off completely
+#if defined(__TINYC__) && defined(__has_include)
 #undef __has_include
 #endif
 
+#if !defined(VNORETURN)
+	#if defined(__TINYC__)
+		#include <stdnoreturn.h>
+		#define VNORETURN noreturn
+	#endif
+	# if !defined(__TINYC__) && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
+	#  define VNORETURN _Noreturn
+	# elif defined(__GNUC__) && __GNUC__ >= 2
+	#  define VNORETURN __attribute__((noreturn))
+	# endif	
+	#ifndef VNORETURN
+		#define VNORETURN
+	#endif
+#endif
+
 //likely and unlikely macros
 #if defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__clang__)
 	#define _likely_(x)  __builtin_expect(x,1)

vlib/v/gen/c/fn.v

@@ -333,6 +333,9 @@ fn (mut g Gen) gen_fn_decl(node &ast.FnDecl, skip bool) {
 	prev_defer_stmts := g.defer_stmts
 	g.defer_stmts = []
 	g.stmts(node.stmts)
+	if node.is_noreturn {
+		g.writeln('\twhile(1);')
+	}
 	// clear g.fn_mut_arg_names
 
 	if !node.has_return {
@@ -1315,10 +1318,23 @@ fn (mut g Gen) write_fn_attrs(attrs []ast.Attr) string {
 			'inline' {
 				g.write('inline ')
 			}
-			'no_inline' {
+			'noinline' {
 				// since these are supported by GCC, clang and MSVC, we can consider them officially supported.
 				g.write('__NOINLINE ')
 			}
+			'noreturn' {
+				// a `[noreturn]` tag tells the compiler, that a function
+				// *DOES NOT RETURN* to its callsites.
+				// See: https://en.cppreference.com/w/c/language/_Noreturn
+				// Such functions should have no return type. They can be used
+				// in places where `panic(err)` or `exit(0)` can be used.
+				// panic/1 and exit/0 themselves will also be marked as
+				// `[noreturn]` soon.
+				// These functions should have busy `for{}` loops injected
+				// at their end, when they do not end by calling other fns
+				// marked by `[noreturn]`.
+				g.write('VNORETURN ')
+			}
 			'irq_handler' {
 				g.write('__IRQHANDLER ')
 			}

vlib/v/gen/native/gen.v

@@ -428,7 +428,6 @@ fn (mut g Gen) postfix_expr(node ast.PostfixExpr) {
 	}
 }
 
-// not yet supported
 [noreturn]
 fn verror(s string) {
 	util.verror('native gen error', s)

vlib/v/parser/fn.v

@@ -185,8 +185,10 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	mut is_exported := false
 	mut is_unsafe := false
 	mut is_trusted := false
+	mut is_noreturn := false
 	for fna in p.attrs {
 		match fna.name {
+			'noreturn' { is_noreturn = true }
 			'manualfree' { is_manualfree = true }
 			'deprecated' { is_deprecated = true }
 			'direct_array_access' { is_direct_arr = true }
@@ -408,6 +410,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			generic_names: generic_names
 			is_pub: is_pub
 			is_deprecated: is_deprecated
+			is_noreturn: is_noreturn
 			is_unsafe: is_unsafe
 			is_main: is_main
 			is_test: is_test
@@ -449,6 +452,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		return_type: return_type
 		return_type_pos: return_type_pos
 		params: params
+		is_noreturn: is_noreturn
 		is_manualfree: is_manualfree
 		is_deprecated: is_deprecated
 		is_exported: is_exported

vlib/v/parser/tests/or_default_missing.out

@@ -1,4 +1,4 @@
-vlib/v/parser/tests/or_default_missing.vv:4:3: error: `or` block must provide a default value of type `int`, or return/exit/continue/break/panic
+vlib/v/parser/tests/or_default_missing.vv:4:3: error: `or` block must provide a default value of type `int`, or return/continue/break or call a [noreturn] function like panic(err) or exit(1)
     2 |     m := [3, 4, 5]
     3 |     el := m[4] or {
     4 |         println('error')

vlib/v/util/errors.v

@@ -141,6 +141,7 @@ pub fn source_context(kind string, source string, pos token.Position) []string {
 	return clines
 }
 
+[noreturn]
 pub fn verror(kind string, s string) {
 	final_kind := bold(color(kind, kind))
 	eprintln('$final_kind: $s')