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fstring.rs
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use alloc::{borrow::ToOwned, boxed::Box, format, string::String, vec, vec::Vec};
use core::{iter, mem, str};
use crate::ast::{ConversionFlag, Expression, Location, StringGroup};
use crate::error::{FStringError, FStringErrorType, ParseError};
use crate::parser::parse_expression;
use self::FStringErrorType::*;
use self::StringGroup::*;
struct FStringParser<'a> {
chars: iter::Peekable<str::Chars<'a>>,
}
impl<'a> FStringParser<'a> {
fn new(source: &'a str) -> Self {
Self {
chars: source.chars().peekable(),
}
}
fn parse_formatted_value(&mut self) -> Result<StringGroup, FStringErrorType> {
let mut expression = String::new();
let mut spec = None;
let mut delims = Vec::new();
let mut conversion = None;
let mut pred_expression_text = String::new();
let mut trailing_seq = String::new();
while let Some(ch) = self.chars.next() {
match ch {
// can be integrated better with the remainign code, but as a starting point ok
// in general I would do here a tokenizing of the fstrings to omit this peeking.
'!' if self.chars.peek() == Some(&'=') => {
expression.push_str("!=");
self.chars.next();
}
'=' if self.chars.peek() == Some(&'=') => {
expression.push_str("==");
self.chars.next();
}
'>' if self.chars.peek() == Some(&'=') => {
expression.push_str(">=");
self.chars.next();
}
'<' if self.chars.peek() == Some(&'=') => {
expression.push_str("<=");
self.chars.next();
}
'!' if delims.is_empty() && self.chars.peek() != Some(&'=') => {
if expression.trim().is_empty() {
return Err(EmptyExpression);
}
conversion = Some(match self.chars.next() {
Some('s') => ConversionFlag::Str,
Some('a') => ConversionFlag::Ascii,
Some('r') => ConversionFlag::Repr,
Some(_) => {
return Err(InvalidConversionFlag);
}
None => {
return Err(ExpectedRbrace);
}
});
if let Some(&peek) = self.chars.peek() {
if peek != '}' && peek != ':' {
return Err(ExpectedRbrace);
}
} else {
return Err(ExpectedRbrace);
}
}
// match a python 3.8 self documenting expression
// format '{' PYTHON_EXPRESSION '=' FORMAT_SPECIFIER? '}'
'=' if self.chars.peek() != Some(&'=') && delims.is_empty() => {
pred_expression_text = expression.to_owned(); // safe expression before = to print it
}
':' if delims.is_empty() => {
let mut nested = false;
let mut in_nested = false;
let mut spec_expression = String::new();
while let Some(&next) = self.chars.peek() {
match next {
'{' => {
if in_nested {
return Err(ExpressionNestedTooDeeply);
}
in_nested = true;
nested = true;
self.chars.next();
continue;
}
'}' => {
if in_nested {
in_nested = false;
self.chars.next();
}
break;
}
_ => (),
}
spec_expression.push(next);
self.chars.next();
}
if in_nested {
return Err(UnclosedLbrace);
}
if nested {
spec = Some(Box::new(FormattedValue {
value: Box::new(
parse_fstring_expr(&spec_expression)
.map_err(|e| InvalidExpression(Box::new(e.error)))?,
),
conversion: None,
spec: None,
}))
} else {
spec = Some(Box::new(Constant {
value: spec_expression.to_owned(),
}))
}
}
'(' | '{' | '[' => {
expression.push(ch);
delims.push(ch);
}
')' => {
if delims.pop() != Some('(') {
return Err(MismatchedDelimiter);
}
expression.push(ch);
}
']' => {
if delims.pop() != Some('[') {
return Err(MismatchedDelimiter);
}
expression.push(ch);
}
'}' if !delims.is_empty() => {
if delims.pop() != Some('{') {
return Err(MismatchedDelimiter);
}
expression.push(ch);
}
'}' => {
if expression.is_empty() {
return Err(EmptyExpression);
}
if pred_expression_text.is_empty() {
return Ok(FormattedValue {
value: Box::new(
parse_fstring_expr(&expression)
.map_err(|e| InvalidExpression(Box::new(e.error)))?,
),
conversion,
spec,
});
} else {
return Ok(Joined {
values: vec![
Constant {
value: pred_expression_text + "=",
},
Constant {
value: trailing_seq,
},
FormattedValue {
value: Box::new(
parse_fstring_expr(&expression)
.map_err(|e| InvalidExpression(Box::new(e.error)))?,
),
conversion,
spec,
},
],
});
}
}
'"' | '\'' => {
expression.push(ch);
while let Some(next) = self.chars.next() {
expression.push(next);
if next == ch {
break;
}
}
}
' ' if !pred_expression_text.is_empty() => {
trailing_seq.push(ch);
}
_ => {
expression.push(ch);
}
}
}
Err(UnclosedLbrace)
}
fn parse(mut self) -> Result<StringGroup, FStringErrorType> {
let mut content = String::new();
let mut values = vec![];
while let Some(ch) = self.chars.next() {
match ch {
'{' => {
if let Some('{') = self.chars.peek() {
self.chars.next();
content.push('{');
} else {
if !content.is_empty() {
values.push(Constant {
value: mem::replace(&mut content, String::new()),
});
}
values.push(self.parse_formatted_value()?);
}
}
'}' => {
if let Some('}') = self.chars.peek() {
self.chars.next();
content.push('}');
} else {
return Err(UnopenedRbrace);
}
}
_ => {
content.push(ch);
}
}
}
if !content.is_empty() {
values.push(Constant { value: content })
}
Ok(match values.len() {
0 => Constant {
value: String::new(),
},
1 => values.into_iter().next().unwrap(),
_ => Joined { values },
})
}
}
fn parse_fstring_expr(source: &str) -> Result<Expression, ParseError> {
let fstring_body = format!("({})", source);
let mut expression = parse_expression(&fstring_body)?;
expression.location.go_left();
Ok(expression)
}
/// Parse an f-string into a string group.
fn parse_fstring(source: &str) -> Result<StringGroup, FStringErrorType> {
FStringParser::new(source).parse()
}
/// Parse an fstring from a string, located at a certain position in the sourcecode.
/// In case of errors, we will get the location and the error returned.
pub fn parse_located_fstring(
source: &str,
location: Location,
) -> Result<StringGroup, FStringError> {
parse_fstring(source).map_err(|error| FStringError { error, location })
}
#[cfg(test)]
mod tests {
use crate::ast;
use super::*;
fn mk_ident(name: &str, row: usize, col: usize) -> ast::Expression {
ast::Expression {
location: ast::Location::new(row, col),
custom: (),
node: ast::ExpressionType::Identifier {
name: name.to_owned(),
},
}
}
#[test]
fn test_parse_fstring() {
let source = String::from("{a}{ b }{{foo}}");
let parse_ast = parse_fstring(&source).unwrap();
assert_eq!(
parse_ast,
Joined {
values: vec![
FormattedValue {
value: Box::new(mk_ident("a", 1, 1)),
conversion: None,
spec: None,
},
FormattedValue {
value: Box::new(mk_ident("b", 1, 2)),
conversion: None,
spec: None,
},
Constant {
value: "{foo}".to_owned()
}
]
}
);
}
#[test]
fn test_parse_fstring_nested_spec() {
let source = String::from("{foo:{spec}}");
let parse_ast = parse_fstring(&source).unwrap();
assert_eq!(
parse_ast,
FormattedValue {
value: Box::new(mk_ident("foo", 1, 1)),
conversion: None,
spec: Some(Box::new(FormattedValue {
value: Box::new(mk_ident("spec", 1, 1)),
conversion: None,
spec: None,
})),
}
);
}
#[test]
fn test_parse_fstring_not_nested_spec() {
let source = String::from("{foo:spec}");
let parse_ast = parse_fstring(&source).unwrap();
assert_eq!(
parse_ast,
FormattedValue {
value: Box::new(mk_ident("foo", 1, 1)),
conversion: None,
spec: Some(Box::new(Constant {
value: "spec".to_owned(),
})),
}
);
}
#[test]
fn test_parse_empty_fstring() {
assert_eq!(
parse_fstring(""),
Ok(Constant {
value: String::new(),
}),
);
}
#[test]
fn test_fstring_parse_selfdocumenting_base() {
let src = String::from("{user=}");
let parse_ast = parse_fstring(&src);
assert!(parse_ast.is_ok());
}
#[test]
fn test_fstring_parse_selfdocumenting_base_more() {
let src = String::from("mix {user=} with text and {second=}");
let parse_ast = parse_fstring(&src);
assert!(parse_ast.is_ok());
}
#[test]
fn test_fstring_parse_selfdocumenting_format() {
let src = String::from("{user=:>10}");
let parse_ast = parse_fstring(&src);
assert!(parse_ast.is_ok());
}
#[test]
fn test_parse_invalid_fstring() {
assert_eq!(parse_fstring("{5!a"), Err(ExpectedRbrace));
assert_eq!(parse_fstring("{5!a1}"), Err(ExpectedRbrace));
assert_eq!(parse_fstring("{5!"), Err(ExpectedRbrace));
assert_eq!(parse_fstring("abc{!a 'cat'}"), Err(EmptyExpression));
assert_eq!(parse_fstring("{!a"), Err(EmptyExpression));
assert_eq!(parse_fstring("{ !a}"), Err(EmptyExpression));
assert_eq!(parse_fstring("{5!}"), Err(InvalidConversionFlag));
assert_eq!(parse_fstring("{5!x}"), Err(InvalidConversionFlag));
assert_eq!(parse_fstring("{a:{a:{b}}"), Err(ExpressionNestedTooDeeply));
assert_eq!(parse_fstring("{a:b}}"), Err(UnopenedRbrace));
assert_eq!(parse_fstring("}"), Err(UnopenedRbrace));
assert_eq!(parse_fstring("{a:{b}"), Err(UnclosedLbrace));
assert_eq!(parse_fstring("{"), Err(UnclosedLbrace));
assert_eq!(parse_fstring("{}"), Err(EmptyExpression));
// TODO: check for InvalidExpression enum?
assert!(parse_fstring("{class}").is_err());
}
#[test]
fn test_parse_fstring_not_equals() {
let source = String::from("{1 != 2}");
let parse_ast = parse_fstring(&source);
assert!(parse_ast.is_ok());
}
#[test]
fn test_parse_fstring_equals() {
let source = String::from("{42 == 42}");
let parse_ast = parse_fstring(&source);
assert!(parse_ast.is_ok());
}
#[test]
fn test_parse_fstring_selfdoc_prec_space() {
let source = String::from("{x =}");
let parse_ast = parse_fstring(&source);
assert!(parse_ast.is_ok());
}
#[test]
fn test_parse_fstring_selfdoc_trailing_space() {
let source = String::from("{x= }");
let parse_ast = parse_fstring(&source);
assert!(parse_ast.is_ok());
}
#[test]
fn test_parse_fstring_yield_expr() {
let source = String::from("{yield}");
let parse_ast = parse_fstring(&source);
assert!(parse_ast.is_ok());
}
}