builtin: fix leaks in `os.execute()` and `[]string{} == []string{}`

vlib/builtin/array.v

@@ -685,8 +685,12 @@ pub fn (a1 []string) eq(a2 []string) bool {
 	if a1.len != a2.len {
 		return false
 	}
+	size_of_string := int(sizeof(string))
 	for i in 0 .. a1.len {
-		if a1[i] != a2[i] {
+		offset := i * size_of_string
+		s1 := &string(unsafe { byteptr(a1.data) + offset })
+		s2 := &string(unsafe { byteptr(a2.data) + offset })
+		if *s1 != *s2 {
 			return false
 		}
 	}

vlib/os/os_nix.c.v

@@ -157,6 +157,7 @@ pub fn mkdir(path string) ?bool {
 }
 
 // execute starts the specified command, waits for it to complete, and returns its output.
+[manualfree]
 pub fn execute(cmd string) Result {
 	// if cmd.contains(';') || cmd.contains('&&') || cmd.contains('||') || cmd.contains('\n') {
 	// return Result{ exit_code: -1, output: ';, &&, || and \\n are not allowed in shell commands' }
@@ -171,6 +172,9 @@ pub fn execute(cmd string) Result {
 	}
 	buf := [4096]byte{}
 	mut res := strings.new_builder(1024)
+	defer {
+		unsafe { res.free() }
+	}
 	unsafe {
 		bufbp := &buf[0]
 		for C.fgets(charptr(bufbp), 4096, f) != 0 {
@@ -178,7 +182,6 @@ pub fn execute(cmd string) Result {
 		}
 	}
 	soutput := res.str()
-	// res.free()
 	exit_code := vpclose(f)
 	return Result{
 		exit_code: exit_code
@@ -196,19 +199,25 @@ pub:
 	redirect_stdout bool
 }
 
-// pub fn command(cmd Command) Command {
-//}
+[manualfree]
 pub fn (mut c Command) start() ? {
-	pcmd := '$c.path 2>&1'
+	pcmd := c.path + ' 2>&1'
+	defer {
+		unsafe { pcmd.free() }
+	}
 	c.f = vpopen(pcmd)
 	if isnil(c.f) {
 		return error('exec("$c.path") failed')
 	}
 }
 
+[manualfree]
 pub fn (mut c Command) read_line() string {
 	buf := [4096]byte{}
 	mut res := strings.new_builder(1024)
+	defer {
+		unsafe { res.free() }
+	}
 	unsafe {
 		bufbp := &buf[0]
 		for C.fgets(charptr(bufbp), 4096, c.f) != 0 {
@@ -216,14 +225,16 @@ pub fn (mut c Command) read_line() string {
 			for i in 0 .. len {
 				if bufbp[i] == `\n` {
 					res.write_ptr(bufbp, i)
-					return res.str()
+					final := res.str()
+					return final
 				}
 			}
 			res.write_ptr(bufbp, len)
 		}
 	}
 	c.eof = true
-	return res.str()
+	final := res.str()
+	return final
 }
 
 pub fn (c &Command) close() ? {