v3: detect wrapped fastc NUL escapes

Author: medvednikov

vlib/v3/gen/fastc/fastc.v

@@ -740,6 +740,20 @@ fn fastc_string_contains_nul(content string, is_raw bool) bool {
 			i += 2
 			continue
 		}
+		if escape >= `0` && escape <= `7` && i + 3 < content.len && content[i + 2] >= `0`
+			&& content[i + 2] <= `7` && content[i + 3] >= `0` && content[i + 3] <= `7` {
+			high := int(escape - `0`)
+			middle := int(content[i + 2] - `0`)
+			low := int(content[i + 3] - `0`)
+			value := high * 64 + middle * 8 + low
+			// V stores three-digit octal escapes in a byte, including wrapping
+			// values such as \400 to NUL.
+			if u8(value) == 0 {
+				return true
+			}
+			i += 4
+			continue
+		}
 		if escape == `0`
 			|| (escape == `x` && i + 3 < content.len && content[i + 2..i + 4] == '00')
 			|| (escape == `u` && i + 5 < content.len && content[i + 2..i + 6] == '0000')

vlib/v3/gen/fastc/fastc_test.v

@@ -128,17 +128,25 @@ fn test_hex_string_escape_has_fixed_width_in_c() {
 
 fn test_runtime_sensitive_constructs_request_checked_lane() {
 	prefs := pref.new_preferences()
-	mut nul_failed := false
-	_ := generate('module main
+	for source in ['module main
 
 fn main() {
 	println("a\\0b")
 }
-', 'nul_string.v', prefs) or {
-		nul_failed = true
-		''
+',
+		"module main\nfn main() { println('\\400tail') }\n"] {
+		mut nul_failed := false
+		_ := generate(source, 'nul_string.v', prefs) or {
+			nul_failed = true
+			''
+		}
+		assert nul_failed
 	}
-	assert nul_failed
+	assert fastc_string_contains_nul(r'\400tail', false)
+	assert !fastc_string_contains_nul(r'\401tail', false)
+	non_nul_octal_c := generate("module main\nfn main() { println('\\401tail') }\n",
+		'non_nul_octal_string.v', prefs) or { panic(err) }
+	assert non_nul_octal_c.contains(r'println("\401tail");')
 
 	mut assert_failed := false
 	_ := generate('module main

vlib/v3/tests/fastc_backend_test.v

@@ -547,6 +547,25 @@ fn main() {
 	assert nul_run.exit_code == 0, nul_run.output.bytes().str()
 	assert nul_run.output == 'a\0b\n', nul_run.output.bytes().str()
 
+	wrapped_nul_source := os.join_path(root, 'wrapped_nul_string.v')
+	os.write_file(wrapped_nul_source, "module main
+
+fn main() {
+	println('\\400tail')
+}
+") or {
+		panic(err)
+	}
+	wrapped_nul_binary := os.join_path(root, 'wrapped_nul_string')
+	wrapped_nul_compile := cmdexec.run(v3_bin, ['-silent', '-b', 'fastc', '-o', wrapped_nul_binary,
+		wrapped_nul_source])
+	assert wrapped_nul_compile.exit_code == 0, wrapped_nul_compile.output
+	wrapped_nul_c := os.read_file(wrapped_nul_binary + '.c') or { panic(err) }
+	assert !wrapped_nul_c.contains('V_FASTC_PRINT_SELECT')
+	wrapped_nul_run := cmdexec.run(wrapped_nul_binary, [])
+	assert wrapped_nul_run.exit_code == 0, wrapped_nul_run.output.bytes().str()
+	assert wrapped_nul_run.output == '\0tail\n', wrapped_nul_run.output.bytes().str()
+
 	assert_source := os.join_path(root, 'assert_failure.v')
 	os.write_file(assert_source, 'module main