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perf: Replace ISO date parser's split/collect with fixed-position structural checks #6

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perf: Replace ISO date parser's split/collect with fixed-position structural checks #6

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Copilot Feb 22, 2026
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perf: Replace ISO split/collect with byte-by-byte parser to avoid all…
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perf: Replace ISO byte-walker with fixed-position structural checks (…
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113 changes: 76 additions & 37 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -218,18 +218,8 @@ impl FromStr for FuzzyDate {
}

if has_hyphen {
// ISO format: YYYY or YYYY-MM or YYYY-MM-DD
let parts: Vec<&str> = trimmed.split(DATE_SEPARATOR).map(str::trim).collect();
match parts.len() {
1 => Self::parse_year_only(parts[0]),
2 => Self::parse_iso_month_year(&parts),
3 => Self::parse_iso_full_date(&parts),
_ => Err(ParseError::InvalidFormat(format!(
"Too many {} separators: expected 0-2, found {}",
DATE_SEPARATOR,
parts.len() - 1
))),
}
// ISO format: YYYY-MM or YYYY-MM-DD (bare YYYY is handled by the else branch)
Self::parse_iso_date(trimmed)
} else if has_slash {
// Month-first format: MM/YYYY or MM/DD/YYYY
Self::parse_slash_date(trimmed)
Expand Down Expand Up @@ -268,36 +258,85 @@ impl FuzzyDate {
types::Day::new(day, year, month)
}

fn parse_iso_month_year(parts: &[&str]) -> Result<Self, ParseError> {
if parts.len() != 2 {
return Err(ParseError::InvalidFormat(parts.join("-")));
/// Dispatch to the right fixed-position ISO parser based on string length.
///
/// Only lengths 7 (`YYYY-MM`) and 10 (`YYYY-MM-DD`) are valid; everything
/// else is an error with a specific message when excess `-` separators are
/// detected.
fn parse_iso_date(s: &str) -> Result<Self, ParseError> {
match s.len() {
7 => Self::parse_iso_7(s),
10 => Self::parse_iso_10(s),
_ => {
let sep_count = s.bytes().filter(|&b| b == b'-').count();
if sep_count > 2 {
Err(ParseError::InvalidFormat(format!(
"Too many {DATE_SEPARATOR} separators: expected 1-2, found {sep_count}"
)))
} else {
Err(ParseError::InvalidFormat(s.to_string()))
}
}
}
// Parse components - InvalidFormat if not numeric
let year_u16 = Self::parse_u16(parts[0])?;
let month_u8 = Self::parse_u8(parts[1])?;

// Validate and convert to NonZero types
let year = Self::validate_and_convert_year(year_u16)?;
let month = Self::validate_and_convert_month(month_u8)?;

Ok(Self::Month { year, month })
}

fn parse_iso_full_date(parts: &[&str]) -> Result<Self, ParseError> {
if parts.len() != 3 {
return Err(ParseError::InvalidFormat(parts.join("-")));
/// Parse `YYYY-MM` (exactly 7 bytes) using fixed-position structural checks.
///
/// Digits must appear at positions 0–3 and 5–6; the only other character
/// must be a `-` at position 4. No heap allocation on success.
fn parse_iso_7(s: &str) -> Result<Self, ParseError> {
let b = s.as_bytes();
if b.len() != 7 {
return Err(ParseError::InvalidFormat(s.to_string()));
}
// Parse components - InvalidFormat if not numeric
let year_u16 = Self::parse_u16(parts[0])?;
let month_u8 = Self::parse_u8(parts[1])?;
let day_u8 = Self::parse_u8(parts[2])?;

// Validate and convert to NonZero types
let year = Self::validate_and_convert_year(year_u16)?;
let month = Self::validate_and_convert_month(month_u8)?;
let day = Self::validate_and_convert_day(year_u16, month_u8, day_u8)?;
if b[0].is_ascii_digit()
&& b[1].is_ascii_digit()
&& b[2].is_ascii_digit()
&& b[3].is_ascii_digit()
&& b[4] == b'-'
&& b[5].is_ascii_digit()
&& b[6].is_ascii_digit()
{
let year_u16 = Self::parse_u16(&s[0..4])?;
let month_u8 = Self::parse_u8(&s[5..7])?;
let year = Self::validate_and_convert_year(year_u16)?;
let month = Self::validate_and_convert_month(month_u8)?;
Ok(Self::Month { year, month })
} else {
Err(ParseError::InvalidFormat(s.to_string()))
}
}

Ok(Self::Day { year, month, day })
/// Parse `YYYY-MM-DD` (exactly 10 bytes) using fixed-position structural checks.
///
/// Digits must appear at positions 0–3, 5–6, and 8–9; `-` separators must
/// appear at positions 4 and 7. No heap allocation on success.
fn parse_iso_10(s: &str) -> Result<Self, ParseError> {
let b = s.as_bytes();
if b.len() != 10 {
return Err(ParseError::InvalidFormat(s.to_string()));
}
if b[0].is_ascii_digit()
&& b[1].is_ascii_digit()
&& b[2].is_ascii_digit()
&& b[3].is_ascii_digit()
&& b[4] == b'-'
&& b[5].is_ascii_digit()
&& b[6].is_ascii_digit()
&& b[7] == b'-'
&& b[8].is_ascii_digit()
&& b[9].is_ascii_digit()
{
let year_u16 = Self::parse_u16(&s[0..4])?;
let month_u8 = Self::parse_u8(&s[5..7])?;
let day_u8 = Self::parse_u8(&s[8..10])?;
let year = Self::validate_and_convert_year(year_u16)?;
let month = Self::validate_and_convert_month(month_u8)?;
let day = Self::validate_and_convert_day(year_u16, month_u8, day_u8)?;
Ok(Self::Day { year, month, day })
} else {
Err(ParseError::InvalidFormat(s.to_string()))
}
}

fn parse_year_only(s: &str) -> Result<Self, ParseError> {
Expand Down