checker: warn when accessing `union` fields outside `unsafe` (#7869)

vlib/strconv/atof.v

@@ -522,6 +522,7 @@ pub fn atof64(s string) f64 {
 
 	res_parsing,pn = parser(s + ' ') // TODO: need an extra char for now
 	// println(pn)
+	unsafe {
 	match res_parsing {
 		parser_ok {
 			res.u = converter(mut pn)
@@ -539,6 +540,8 @@ pub fn atof64(s string) f64 {
 			res.u = double_minus_infinity
 		}
 		else {
-		}}
+		}
+	}
 	return res.f
+	}
 }

vlib/strconv/atofq.v

@@ -37,6 +37,7 @@ pub fn atof_quick(s string) f64 {
 			i++
 		}
 	}
+	unsafe {
 	// infinite
 	if s[i] == `i` && i + 2 < s.len && s[i + 1] == `n` && s[i + 2] == `f` {
 		if sign > 0.0 {
@@ -133,6 +134,7 @@ pub fn atof_quick(s string) f64 {
 	}
 	f.f = f.f * sign
 	return f.f
+	}
 }
 
 const (

vlib/strconv/f32_str.v

@@ -321,8 +321,8 @@ pub fn f32_to_decimal(mant u32, exp u32) Dec32 {
 // f32_to_str return a string in scientific notation with max n_digit after the dot
 pub fn f32_to_str(f f32, n_digit int) string {
 	mut u1 := Uf32{}
-	u1.f = f
-	u := u1.u
+	unsafe { u1.f = f }
+	u := unsafe {u1.u}
 
 	neg   := (u>>(mantbits32+expbits32)) != 0
 	mant  := u & ((u32(1)<<mantbits32) - u32(1))
@@ -348,8 +348,8 @@ pub fn f32_to_str(f f32, n_digit int) string {
 // f32_to_str return a string in scientific notation with max n_digit after the dot
 pub fn f32_to_str_pad(f f32, n_digit int) string {
 	mut u1 := Uf32{}
-	u1.f = f
-	u := u1.u
+	unsafe { u1.f = f }
+	u := unsafe {u1.u}
 
 	neg   := (u>>(mantbits32+expbits32)) != 0
 	mant  := u & ((u32(1)<<mantbits32) - u32(1))

vlib/strconv/f64_str.v

@@ -370,8 +370,8 @@ fn f64_to_decimal(mant u64, exp u64) Dec64 {
 // f64_to_str return a string in scientific notation with max n_digit after the dot
 pub fn f64_to_str(f f64, n_digit int) string {
 	mut u1 := Uf64{}
-	u1.f = f
-	u := u1.u
+	unsafe { u1.f = f }
+	u := unsafe {u1.u}
 
 	neg   := (u>>(mantbits64+expbits64)) != 0
 	mant  := u & ((u64(1)<<mantbits64) - u64(1))
@@ -395,8 +395,8 @@ pub fn f64_to_str(f f64, n_digit int) string {
 // f64_to_str return a string in scientific notation with max n_digit after the dot
 pub fn f64_to_str_pad(f f64, n_digit int) string {
 	mut u1 := Uf64{}
-	u1.f = f
-	u := u1.u
+	unsafe { u1.f = f }
+	u := unsafe {u1.u}
 
 	neg   := (u>>(mantbits64+expbits64)) != 0
 	mant  := u & ((u64(1)<<mantbits64) - u64(1))

vlib/v/checker/checker.v

@@ -1050,6 +1050,9 @@ fn (mut c Checker) fail_if_immutable(expr ast.Expr) (string, token.Position) {
 						// No automatic lock for struct access
 						explicit_lock_needed = true
 					}
+					if struct_info.is_union && !c.inside_unsafe {
+						c.warn('accessing union fields requires `unsafe`', expr.pos)
+					}
 				}
 				.array, .string {
 					// This should only happen in `builtin`