Precedence parsing (#1362)

* Initial prototype

* Update docs
Remove unused code

* More doc updates

* Add feature flags for Vec

* Add basic tests

* Fix formatting

* Add precedence to choosing_a_combinator.md

* Fix typo

* Minor refractoring

* Update docs

* Change parameter order

* Add alloc feature to the entire precedence module

The parser really cant work without it and the helpers dont make much sense without the parser.

* Use fail parser to express "no operators of this type"

* Document evaluation order

* Better documentation for parameters

* Fix precedence in documentation

* Fix doc formatting

* Fix typos

* Use map_res when parsing integers

* Example test for expressions with function calls and AST generation

* Typo

* Make evaluation a bit easier to read

* Update expression_ast

* Update expression_ast doc

* Implement ternary operator in expression_ast

* Shorten ast nodes

* Implement some tests for parser failures

* Update feature flags for docs

* Properly append errors

* Properly bubble up non Error errors

* Split operators into 3 distinct types to help with exhaustiveness checks.

---------

Co-authored-by: Geoffroy Couprie <[email protected]>

Cargo.toml

@@ -66,6 +66,10 @@ name = "css"
 [[test]]
 name = "custom_errors"
 
+[[test]]
+name = "expression_ast"
+required-features = ["alloc"]
+
 [[test]]
 name = "float"
 

doc/choosing_a_combinator.md

@@ -106,6 +106,7 @@ The following parsers could be found on [docs.rs number section](https://docs.rs
 
 - [`escaped`](https://docs.rs/nom/latest/nom/bytes/complete/fn.escaped.html): Matches a byte string with escaped characters
 - [`escaped_transform`](https://docs.rs/nom/latest/nom/bytes/complete/fn.escaped_transform.html): Matches a byte string with escaped characters, and returns a new string with the escaped characters replaced
+- [`precedence`](https://docs.rs/nom/latest/nom/precedence/fn.precedence.html): Parses an expression with regards to operator precedence
 
 ## Binary format parsing
 

src/error.rs

@@ -310,6 +310,7 @@ pub enum ErrorKind {
   Fail,
   Many,
   Fold,
+  Precedence,
 }
 
 #[rustfmt::skip]
@@ -373,6 +374,7 @@ pub fn error_to_u32(e: &ErrorKind) -> u32 {
     ErrorKind::Many                      => 76,
     ErrorKind::Fold                      => 77,
     ErrorKind::BinDigit                  => 78,
+    ErrorKind::Precedence                => 79,
   }
 }
 
@@ -438,6 +440,7 @@ impl ErrorKind {
       ErrorKind::Fail                      => "Fail",
       ErrorKind::Many                      => "Many",
       ErrorKind::Fold                      => "Fold",
+      ErrorKind::Precedence                => "Precedence",
     }
   }
 }

src/lib.rs

@@ -451,6 +451,8 @@ pub mod bytes;
 
 pub mod character;
 
+pub mod precedence;
+
 mod str;
 
 pub mod number;