feat(builtins): full sort -k KEYDEF parsing with multi-key support

Parse the complete GNU sort key spec: start/end fields (-k2,3),
character positions (-k2.3,3.4), per-key flags (-k2n,2 -k3r,3),
and multiple keys for cascading sort priority.

Closes #906

Author: chaliy

crates/bashkit/src/builtins/sortuniq.rs

@@ -25,22 +25,152 @@ use crate::interpreter::ExecResult;
 ///   -o   Write output to FILE
 pub struct Sort;
 
-/// Extract the sort key from a line based on field delimiter and key spec
-fn extract_key(line: &str, delimiter: Option<char>, key_field: usize) -> String {
+/// A parsed sort key definition from `-k KEYDEF`.
+/// Format: `START[.CHAR][FLAGS][,END[.CHAR][FLAGS]]`
+#[derive(Clone, Debug)]
+struct KeySpec {
+    start_field: usize,
+    start_char: usize, // 0 = whole field
+    end_field: usize,  // 0 = end of line
+    end_char: usize,   // 0 = end of field
+    numeric: bool,
+    reverse: bool,
+    fold_case: bool,
+    human_numeric: bool,
+    month_sort: bool,
+    #[allow(dead_code)] // Used when combined with sort -V feature
+    version_sort: bool,
+}
+
+impl KeySpec {
+    /// Parse a KEYDEF string like "2", "2,3", "2.3,3.4", "2n,2", "2nr"
+    fn parse(spec: &str) -> Self {
+        let (start_part, end_part) = if let Some(comma) = spec.find(',') {
+            (&spec[..comma], Some(&spec[comma + 1..]))
+        } else {
+            (spec, None)
+        };
+
+        let (start_field, start_char, start_flags) = Self::parse_field_spec(start_part);
+        let (end_field, end_char, end_flags) = if let Some(ep) = end_part {
+            let (f, c, fl) = Self::parse_field_spec(ep);
+            (f, c, fl)
+        } else {
+            (0, 0, String::new())
+        };
+
+        // Merge flags from both start and end parts
+        let all_flags: String = format!("{}{}", start_flags, end_flags);
+
+        KeySpec {
+            start_field,
+            start_char,
+            end_field,
+            end_char,
+            numeric: all_flags.contains('n'),
+            reverse: all_flags.contains('r'),
+            fold_case: all_flags.contains('f'),
+            human_numeric: all_flags.contains('h'),
+            month_sort: all_flags.contains('M'),
+            version_sort: all_flags.contains('V'),
+        }
+    }
+
+    /// Parse "FIELD[.CHAR][FLAGS]" → (field, char_pos, flags_string)
+    fn parse_field_spec(s: &str) -> (usize, usize, String) {
+        let mut i = 0;
+        let chars: Vec<char> = s.chars().collect();
+        // Parse field number
+        while i < chars.len() && chars[i].is_ascii_digit() {
+            i += 1;
+        }
+        let field: usize = s[..i].parse().unwrap_or(0);
+
+        // Parse optional .CHAR
+        let mut char_pos = 0;
+        if i < chars.len() && chars[i] == '.' {
+            i += 1;
+            let start = i;
+            while i < chars.len() && chars[i].is_ascii_digit() {
+                i += 1;
+            }
+            char_pos = s[start..i].parse().unwrap_or(0);
+        }
+
+        // Remaining chars are flags
+        let flags = s[i..].to_string();
+        (field, char_pos, flags)
+    }
+}
+
+/// Split a line into fields using the given delimiter
+fn split_fields(line: &str, delimiter: Option<char>) -> Vec<&str> {
     if let Some(delim) = delimiter {
-        line.split(delim)
-            .nth(key_field.saturating_sub(1))
-            .unwrap_or("")
-            .to_string()
+        line.split(delim).collect()
     } else {
-        // Default: whitespace-separated fields
-        line.split_whitespace()
-            .nth(key_field.saturating_sub(1))
-            .unwrap_or("")
-            .to_string()
+        line.split_whitespace().collect()
     }
 }
 
+/// Extract the sort key from a line based on field delimiter and key spec
+fn extract_key_spec(line: &str, delimiter: Option<char>, key: &KeySpec) -> String {
+    let fields = split_fields(line, delimiter);
+    if fields.is_empty() || key.start_field == 0 {
+        return line.to_string();
+    }
+
+    let start_idx = key.start_field.saturating_sub(1);
+    if start_idx >= fields.len() {
+        return String::new();
+    }
+
+    let end_idx = if key.end_field == 0 {
+        fields.len() - 1
+    } else {
+        (key.end_field.saturating_sub(1)).min(fields.len() - 1)
+    };
+
+    if start_idx > end_idx {
+        return String::new();
+    }
+
+    if start_idx == end_idx {
+        let field = fields[start_idx];
+        let start_c = if key.start_char > 0 {
+            (key.start_char - 1).min(field.len())
+        } else {
+            0
+        };
+        let end_c = if key.end_char > 0 {
+            key.end_char.min(field.len())
+        } else {
+            field.len()
+        };
+        if start_c >= end_c {
+            return String::new();
+        }
+        return field[start_c..end_c].to_string();
+    }
+
+    // Multi-field key
+    let mut result = String::new();
+    for (i, field) in fields.iter().enumerate().take(end_idx + 1).skip(start_idx) {
+        if i > start_idx {
+            result.push(delimiter.unwrap_or(' '));
+        }
+        if i == start_idx && key.start_char > 0 {
+            let sc = (key.start_char - 1).min(field.len());
+            result.push_str(&field[sc..]);
+        } else if i == end_idx && key.end_char > 0 {
+            let ec = key.end_char.min(field.len());
+            result.push_str(&field[..ec]);
+        } else {
+            result.push_str(field);
+        }
+    }
+    result
+}
+
 /// Extract leading numeric prefix from a string for `sort -n`.
 /// Real coreutils `sort -n` parses the leading numeric portion (optional sign,
 /// digits, optional decimal point and digits) and treats the rest as non-numeric.
@@ -124,7 +254,7 @@ impl Builtin for Sort {
         let mut month_sort = false;
         let mut merge = false;
         let mut delimiter: Option<char> = None;
-        let mut key_field: Option<usize> = None;
+        let mut key_specs: Vec<KeySpec> = Vec::new();
         let mut output_file: Option<String> = None;
         let mut zero_terminated = false;
         let mut files = Vec::new();
@@ -134,15 +264,7 @@ impl Builtin for Sort {
             if let Some(val) = p.flag_value_opt("-t") {
                 delimiter = val.chars().next();
             } else if let Some(val) = p.flag_value_opt("-k") {
-                // Parse key: "2" or "2,2" or "2n"
-                let field_str: String = val.chars().take_while(|c| c.is_ascii_digit()).collect();
-                key_field = field_str.parse().ok();
-                if val.contains('n') {
-                    numeric = true;
-                }
-                if val.contains('r') {
-                    reverse = true;
-                }
+                key_specs.push(KeySpec::parse(val));
             } else if let Some(val) = p.flag_value_opt("-o") {
                 output_file = Some(val.to_string());
             } else {
@@ -280,43 +402,59 @@ impl Builtin for Sort {
         }
 
         // Get the key extractor
-        let get_key = |line: &str| -> String {
-            if let Some(kf) = key_field {
-                extract_key(line, delimiter, kf)
+        /// Compare two keys using the specified sort mode flags
+        fn compare_keys(
+            ka: &str,
+            kb: &str,
+            is_numeric: bool,
+            is_human: bool,
+            is_month: bool,
+            is_fold_case: bool,
+        ) -> std::cmp::Ordering {
+            if is_human {
+                let na = parse_human_numeric(ka);
+                let nb = parse_human_numeric(kb);
+                na.partial_cmp(&nb).unwrap_or(std::cmp::Ordering::Equal)
+            } else if is_month {
+                month_ordinal(ka).cmp(&month_ordinal(kb))
+            } else if is_numeric {
+                let na = extract_numeric_prefix(ka);
+                let nb = extract_numeric_prefix(kb);
+                na.partial_cmp(&nb).unwrap_or(std::cmp::Ordering::Equal)
+            } else if is_fold_case {
+                ka.to_lowercase().cmp(&kb.to_lowercase())
             } else {
-                line.to_string()
+                ka.cmp(kb)
             }
-        };
+        }
 
         // Sort the lines
         let sort_fn = |a: &String, b: &String| -> std::cmp::Ordering {
-            let ka = get_key(a);
-            let kb = get_key(b);
-            if human_numeric {
-                let na = parse_human_numeric(&ka);
-                let nb = parse_human_numeric(&kb);
-                na.partial_cmp(&nb).unwrap_or(std::cmp::Ordering::Equal)
-            } else if month_sort {
-                let ma = month_ordinal(&ka);
-                let mb = month_ordinal(&kb);
-                ma.cmp(&mb)
-            } else if numeric {
-                let na = extract_numeric_prefix(&ka);
-                let nb = extract_numeric_prefix(&kb);
-                match na.partial_cmp(&nb).unwrap_or(std::cmp::Ordering::Equal) {
-                    std::cmp::Ordering::Equal => a.cmp(b),
-                    ord => ord,
-                }
-            } else if fold_case {
-                let ord = ka.to_lowercase().cmp(&kb.to_lowercase());
-                if ord == std::cmp::Ordering::Equal && key_field.is_some() {
-                    a.cmp(b)
-                } else {
-                    ord
+            if !key_specs.is_empty() {
+                // Multi-key sort: compare by each key spec in order
+                for key in &key_specs {
+                    let ka = extract_key_spec(a, delimiter, key);
+                    let kb = extract_key_spec(b, delimiter, key);
+                    // Per-key flags override global flags
+                    let ord = compare_keys(
+                        &ka,
+                        &kb,
+                        key.numeric || numeric,
+                        key.human_numeric || human_numeric,
+                        key.month_sort || month_sort,
+                        key.fold_case || fold_case,
+                    );
+                    let ord = if key.reverse { ord.reverse() } else { ord };
+                    if ord != std::cmp::Ordering::Equal {
+                        return ord;
+                    }
                 }
+                // All keys equal — fall back to full-line comparison
+                a.cmp(b)
             } else {
-                let ord = ka.cmp(&kb);
-                if ord == std::cmp::Ordering::Equal && key_field.is_some() {
+                // No key specs — use global flags on whole line
+                let ord = compare_keys(a, b, numeric, human_numeric, month_sort, fold_case);
+                if ord == std::cmp::Ordering::Equal {
                     a.cmp(b)
                 } else {
                     ord

crates/bashkit/tests/spec_cases/bash/sortuniq.test.sh

@@ -332,3 +332,49 @@ printf '003\n010\n001\n' | sort -n
 003
 010
 ### end
+
+### sort_key_end_field
+# sort -k with start,end field spec
+printf 'c 3\na 1\nb 2\n' | sort -k2,2
+### expect
+a 1
+b 2
+c 3
+### end
+
+### sort_key_numeric_per_key
+# sort -k with per-key numeric flag
+printf 'a 10\nb 2\nc 1\n' | sort -k2n,2
+### expect
+c 1
+b 2
+a 10
+### end
+
+### sort_key_multiple
+# sort with multiple -k keys (primary lexical, secondary numeric)
+printf 'b 2\na 10\na 2\nb 1\n' | sort -k1,1 -k2n,2
+### expect
+a 2
+a 10
+b 1
+b 2
+### end
+
+### sort_key_reverse_per_key
+# sort -k with per-key reverse flag
+printf 'a 1\nb 2\nc 3\n' | sort -k2r,2
+### expect
+c 3
+b 2
+a 1
+### end
+
+### sort_key_char_position
+# sort -k with character positions
+printf 'abc\naab\nabc\n' | sort -k1.2,1.2
+### expect
+aab
+abc
+abc
+### end