rubble_templates_evaluators/

parser.rs

//! Default parser logic

use log::{debug, trace, log_enabled, Level};
use rubble_templates_core::ast::SyntaxNode;
use rubble_templates_core::units::Position;

/// Used for parsing AST for further evaluation.
///
/// This function tries to parse AST assuming it is Lisp-like syntax, which is practically
/// `function arg0 arg1 arg2`, where `function` is the function name, and `arg0...` are the arguments.
///
/// It also allows to use parenthesis to evaluate a nested function.
///
/// Reserved characters (cannot be used in names):
/// * ` ` - space
/// * `(` - left parenthesis
/// * `)` - right parenthesis
///
/// Examples:
/// * `(function 1 2 3)` - interpreted as `function` call with parameters `1`, `2` and `3`
/// * `plus 1 2 (times 3 4)` - interpreted as `1 + 2 + (3 * 4)`, given `plus` is an addition function and `times` is a multiplication function
///
pub fn parse_ast(source: &str, code_start: &str, code_end: &str) -> SyntaxNode {
    if log_enabled!(Level::Debug) {
        debug!("Starting to parse AST of: {}", source);
    }
    let source = source.strip_prefix(code_start).unwrap_or(source);
    let source = source.strip_suffix(code_end).unwrap_or(source);

    let result = next_node_of(source, 0, 0).0;
    if log_enabled!(Level::Debug) {
        debug!("Parsing complete, result: {:?}", result);
    }
    result
}

struct SyntaxScanResult(SyntaxNode, usize);

fn next_node_of(source: &str, offset: usize, level: usize) -> SyntaxScanResult {
    if log_enabled!(Level::Trace) {
        trace!("{:->width$}>{}", "", source, width = level);
    }
    let mut syntax_node = SyntaxNode::AnonymousNode {
        children: vec![],
        starts_at: Position::RelativeToCodeStart(offset),
    };
    let mut identifier = "".to_string();
    let mut string_started = false;
    let mut identifier_start: usize = offset;
    let mut skip_end: usize = 0;
    let mut source_length: usize = 0;

    for (index, char) in source.chars().enumerate() {
        let position = offset + index;
        source_length += 1;
        if position <= skip_end {
            continue;
        }
        let current_offset = index + 1;

        let (id, started) = extract_string(identifier, char, string_started);
        identifier = id;
        string_started = started;
        if string_started {
            continue;
        }

        if char == '(' {
            let (new_node, skip_pos) = start_node(syntax_node, &identifier, &source[current_offset..], identifier_start + 1, position, level);
            syntax_node = new_node;
            skip_end = skip_pos;
        } else {
            if char == ' ' || char == ')' {
                syntax_node = add_identifier_or_child(
                    syntax_node,
                    &identifier,
                    identifier_start + 1,
                    level,
                );
                identifier.clear();
                identifier_start = position + 1;
            } else {
                identifier.push(char);
            }

            if char == ')' {
                if log_enabled!(Level::Trace) {
                    trace!("{:->width$}Parsing of the following fragment is complete (finished at {}): {}, result: {:?}", "", position, source, syntax_node, width = level);
                }
                return SyntaxScanResult(syntax_node, position);
            }
        }
    }

    let end_pos = offset + source_length;
    if log_enabled!(Level::Trace) {
        trace!("{:->width$}Parsing of the following fragment is complete (finished at {}): {}, result: {:?}", "", end_pos, source, syntax_node, width = level);
    }
    SyntaxScanResult(syntax_node, end_pos)
}

fn extract_string(identifier: String, char: char, string_started: bool) -> (String, bool) {
    let mut identifier = identifier;
    let mut string_started = string_started;

    if string_started && char != '"' {
        identifier.push(char);
    } else if string_started {
        string_started = false;
    } else if char == '"' {
        identifier.push(char);
        string_started = true;
    }

    (identifier, string_started)
}

fn start_node(syntax_node: SyntaxNode, identifier: &str, source_remainder: &str, identifier_start: usize, position: usize, level: usize) -> (SyntaxNode, usize) {
    let mut syntax_node = syntax_node;
    syntax_node = add_identifier_or_child(
        syntax_node,
        identifier,
        identifier_start,
        level,
    );

    let SyntaxScanResult(child, skip_pos) = next_node_of(source_remainder, position, level + 1);
    syntax_node = syntax_node.add_child(child);

    (syntax_node, skip_pos)
}

fn add_identifier_or_child(syntax_node: SyntaxNode, new_identifier: &str, identifier_starts_at: usize, level: usize) -> SyntaxNode {
    if new_identifier.is_empty() {
        return syntax_node;
    }

    trace!("{:->width$}+\"{}\" at {}", "", new_identifier, identifier_starts_at, width = level);

    if syntax_node.is_anonymous() {
        syntax_node.with_identifier(new_identifier, Position::RelativeToCodeStart(identifier_starts_at))

    } else {
        if log_enabled!(Level::Trace) {
            trace!("{:->width$}-\"{}\" at {} (child of {})", "", new_identifier, identifier_starts_at, syntax_node, width = level);
        }
        syntax_node.add_child(SyntaxNode::NamedNode {
                identifier: new_identifier.to_string(),
                children: vec![],
                starts_at: Position::RelativeToCodeStart(identifier_starts_at),
            })
    }
}

#[cfg(test)]
mod tests {
    use rubble_templates_core::ast::SyntaxNode::{AnonymousNode, NamedNode};
    use log::LevelFilter;
    use rubble_templates_core::units::Position;
    use crate::parser::parse_ast;

    fn init() {
        let _ = env_logger::builder()
            .filter_level(LevelFilter::Trace)
            .is_test(true)
            .try_init();
    }

    #[test]
    fn should_parse_ast() {
        init();

        let input = "{{ (list 1 2 (if a b c)) }}";
        let actual = parse_ast(input,"{{", "}}");

        let expected = AnonymousNode {
            starts_at: Position::RelativeToCodeStart(0),
            children: vec![
                NamedNode {
                    identifier: "list".to_string(),
                    starts_at: Position::RelativeToCodeStart(2),
                    children: vec![
                        NamedNode {
                            identifier: "1".to_string(),
                            children: vec![],
                            starts_at: Position::RelativeToCodeStart(7),
                        },
                        NamedNode {
                            identifier: "2".to_string(),
                            starts_at: Position::RelativeToCodeStart(9),
                            children: vec![],
                        },
                        NamedNode {
                            identifier: "if".to_string(),
                            starts_at: Position::RelativeToCodeStart(11),
                            children: vec![
                                NamedNode {
                                    identifier: "a".to_string(),
                                    starts_at: Position::RelativeToCodeStart(14),
                                    children: vec![],
                                },
                                NamedNode {
                                    identifier: "b".to_string(),
                                    starts_at: Position::RelativeToCodeStart(16),
                                    children: vec![],
                                },
                                NamedNode {
                                    identifier: "c".to_string(),
                                    starts_at: Position::RelativeToCodeStart(18),
                                    children: vec![],
                                },
                            ],
                        },
                    ],
                },
            ],
        };
        assert_eq!(expected, actual);
    }
}