feat: PromQL Rust Lexer (#12)

* feat(lex): skeleton

* refactor(lexer): use enum instead of trait object

* lex: keyword_or_identifier

* fix(ctx): pos, start, peek logic

* refactor: fn -> Fn

* refactor: move shift into Lexer

* lexer: accept_string

* lexer: duration, lable_selector

* example: make example work with lexer

* test: common test done

* test(lex): more test cases

* test(lex): unbalanced parentheses

* test(lexer): subquery

* test(lexer): more cases

* test: token and production fn

* misc(lex): modification based on review comments

- don't expose some public methods
- refactor test cases

Reviewer: @evenyag
Refs: #14 #15

* misc(lex): revision based on review comment

- func in token mod, directly use match arms
- use char default method, instead of a hashmap
- use for loop to asset_eq!(left, right) instead of assert!(all)

reviewer: @evenyag

* misc(lex): use const instead of lazy_static

* perf(token): use hashmap instead of match on &str

* fix(lex): potential panic try to dec depth when depth is less than 1

* misc(lex): use usize instead of u8 for paren_depth

* feat(lex): to check if backup is at the beginning of input

* comment(lex): typo

.gitignore

@@ -1,6 +1,7 @@
 # Generated by Cargo
 # will have compiled files and executables
 /target/
+.vscode
 
 # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
 # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html

examples/parser.rs

@@ -15,9 +15,10 @@
 use promql_parser::parser;
 
 fn main() {
-    let promql = "node_cpu_seconds_total{cpu=0,mode=idle}";
+    let promql = r#"prometheus_http_requests_total{code="200", job="prometheus"}"#;
 
-    let ast = parser::parse(promql).unwrap();
-
-    println!("AST: {:?}", ast);
+    match parser::parse(promql) {
+        Ok(ast) => println!("AST: {:?}", ast),
+        Err(info) => println!("Err: {:?}", info),
+    }
 }

src/label/matcher.rs

@@ -12,8 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::parser::Token;
-use crate::parser::{T_EQL, T_EQL_REGEX, T_NEQ, T_NEQ_REGEX};
+use crate::parser::token::{Token, T_EQL, T_EQL_REGEX, T_NEQ, T_NEQ_REGEX};
 use regex::Regex;
 
 #[derive(Debug)]