feat: use backslash at end of line for multiline text (#147)

BREAKING CHANGE: use backslash at end of line for multiline text

```
〉.set dry_run true

〉abc \
def \
ijk

>>> The following message consumes 12 tokens.
abc 
def 
ijk
```

Deprecate old {}/() multi-line editing

src/repl/mod.rs

@@ -16,7 +16,6 @@ use crate::term;
 
 use anyhow::{Context, Result};
 use reedline::Signal;
-use std::borrow::Cow;
 use std::rc::Rc;
 
 pub const REPL_COMMANDS: [(&str, &str); 13] = [
@@ -86,7 +85,7 @@ impl Repl {
     }
 
     fn handle_line(&mut self, handler: &Rc<ReplCmdHandler>, line: &str) -> Result<bool> {
-        let line = clean_multiline_symbols(line);
+        let line = line.trim().replace("\\\n", "\n");
         match parse_command(line.as_ref()) {
             Some((cmd, args)) => match cmd {
                 ".exit" => {
@@ -165,21 +164,12 @@ fn dump_repl_help() {
     print_now!(
         r###"{head}
 
-Type `{{` to enter the multi-line editing mode, type '}}' to exit the mode.
 Press Ctrl+C to abort readline, Ctrl+D to exit the REPL
 
 "###,
     );
 }
 
-fn clean_multiline_symbols(line: &str) -> Cow<str> {
-    let trimed_line = line.trim();
-    match trimed_line.chars().next() {
-        Some('{' | '[' | '(') => trimed_line[1..trimed_line.len() - 1].into(),
-        _ => Cow::Borrowed(line),
-    }
-}
-
 fn parse_command(line: &str) -> Option<(&str, Option<&str>)> {
     let mut trimed_line = line.trim_start();
     if trimed_line.starts_with('.') {

src/repl/validator.rs

@@ -6,55 +6,10 @@ pub struct ReplValidator;
 
 impl Validator for ReplValidator {
     fn validate(&self, line: &str) -> ValidationResult {
-        if incomplete_brackets(line) {
+        if line.ends_with('\\') {
             ValidationResult::Incomplete
         } else {
             ValidationResult::Complete
         }
     }
 }
-
-fn incomplete_brackets(line: &str) -> bool {
-    let mut balance: Vec<char> = Vec::new();
-    let mut symbol = None;
-    for c in line.chars() {
-        match symbol {
-            Some(s) => match (s, c) {
-                ('{', '}') | ('(', ')') => {
-                    balance.pop();
-                }
-                _ if s == c => {
-                    balance.push(c);
-                }
-                _ => {}
-            },
-            None => match c {
-                '{' | '(' => {
-                    balance.push(c);
-                    symbol = Some(c);
-                }
-                _ => {}
-            },
-        }
-    }
-
-    !balance.is_empty()
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_incomplete_brackets() {
-        assert!(incomplete_brackets("{"));
-        assert!(incomplete_brackets("("));
-        assert!(!incomplete_brackets("{}"));
-        assert!(!incomplete_brackets("()"));
-        assert!(!incomplete_brackets("{ab\nc}"));
-        assert!(!incomplete_brackets("(ab\nc)"));
-        assert!(!incomplete_brackets("{[}"));
-        assert!(!incomplete_brackets("{{{{{}}}}}"));
-        assert!(incomplete_brackets("{{}"));
-    }
-}