fix(parser): handle $'...' ANSI-C quoting in parameter expansion patterns (#856)

Closes #847

Author: chaliy

crates/bashkit/src/interpreter/mod.rs

@@ -6438,19 +6438,23 @@ impl Interpreter {
             }
             ParameterOp::RemovePrefixShort => {
                 // ${var#pattern} - remove shortest prefix match
-                self.remove_pattern(value, operand, true, false)
+                let expanded = self.expand_operand(operand);
+                self.remove_pattern(value, &expanded, true, false)
             }
             ParameterOp::RemovePrefixLong => {
                 // ${var##pattern} - remove longest prefix match
-                self.remove_pattern(value, operand, true, true)
+                let expanded = self.expand_operand(operand);
+                self.remove_pattern(value, &expanded, true, true)
             }
             ParameterOp::RemoveSuffixShort => {
                 // ${var%pattern} - remove shortest suffix match
-                self.remove_pattern(value, operand, false, false)
+                let expanded = self.expand_operand(operand);
+                self.remove_pattern(value, &expanded, false, false)
             }
             ParameterOp::RemoveSuffixLong => {
                 // ${var%%pattern} - remove longest suffix match
-                self.remove_pattern(value, operand, false, true)
+                let expanded = self.expand_operand(operand);
+                self.remove_pattern(value, &expanded, false, true)
             }
             ParameterOp::ReplaceFirst {
                 pattern,

crates/bashkit/src/parser/mod.rs

@@ -2534,8 +2534,38 @@ impl<'a> Parser<'a> {
                     parts.push(WordPart::Literal(std::mem::take(&mut current)));
                 }
 
-                // Check for $( - command substitution or arithmetic
-                if chars.peek() == Some(&'(') {
+                // Check for $'...' - ANSI-C quoting
+                if chars.peek() == Some(&'\'') {
+                    chars.next(); // consume opening '
+                    let mut ansi = String::new();
+                    while let Some(c) = chars.next() {
+                        if c == '\'' {
+                            break;
+                        }
+                        if c == '\\' {
+                            if let Some(esc) = chars.next() {
+                                match esc {
+                                    'n' => ansi.push('\n'),
+                                    't' => ansi.push('\t'),
+                                    'r' => ansi.push('\r'),
+                                    'a' => ansi.push('\x07'),
+                                    'b' => ansi.push('\x08'),
+                                    'e' | 'E' => ansi.push('\x1B'),
+                                    '\\' => ansi.push('\\'),
+                                    '\'' => ansi.push('\''),
+                                    _ => {
+                                        ansi.push('\\');
+                                        ansi.push(esc);
+                                    }
+                                }
+                            }
+                        } else {
+                            ansi.push(c);
+                        }
+                    }
+                    parts.push(WordPart::Literal(ansi));
+                } else if chars.peek() == Some(&'(') {
+                    // Check for $( - command substitution or arithmetic
                     chars.next(); // consume first '('
 
                     // Check for $(( - arithmetic expansion

crates/bashkit/tests/spec_cases/bash/blackbox-edge-cases.test.sh

@@ -587,11 +587,10 @@ file3.txt
 ### end
 
 ### chained_string_operations
-### bash_diff: variable expansion in ${x#$var} operand not supported yet
-# Multiple string operations — bash: "[hello world  ]", bashkit: "[  hello world  ]"
+# Multiple string operations — strip leading whitespace
 x="  hello world  "; x="${x#"${x%%[![:space:]]*}"}"; echo "[$x]"
 ### expect
-[  hello world  ]
+[hello world  ]
 ### end
 
 ### multiline_if

crates/bashkit/tests/spec_cases/bash/var-op-test.test.sh

@@ -248,3 +248,49 @@ empty=
 assoc=v
 assoc=plus
 ### end
+
+### vop_suffix_removal_ansi_c_newline
+# ${var%$'\n'} should strip trailing newline (issue #847)
+str=$'abc\n'
+r1="${str%$'\n'}"
+echo "$r1"
+### expect
+abc
+### end
+
+### vop_suffix_removal_var_newline
+# ${var%${nl}} should strip trailing newline via variable (issue #847)
+nl=$'\n'
+str=$'abc\n'
+r2="${str%${nl}}"
+echo "$r2"
+### expect
+abc
+### end
+
+### vop_prefix_removal_ansi_c_newline
+# ${var#$'\n'} should strip leading newline (issue #847)
+str=$'\nabc'
+r3="${str#$'\n'}"
+echo "$r3"
+### expect
+abc
+### end
+
+### vop_suffix_removal_long_ansi_c
+# ${var%%$'\n'} should strip trailing newline (issue #847)
+str=$'abc\n'
+r4="${str%%$'\n'}"
+echo "$r4"
+### expect
+abc
+### end
+
+### vop_prefix_removal_long_ansi_c
+# ${var##$'\n'} should strip leading newline (issue #847)
+str=$'\nabc'
+r5="${str##$'\n'}"
+echo "$r5"
+### expect
+abc
+### end