Function strip_outer_parens

src/code_actions/extract_variable.rs:24–49

Strip a single layer of balanced outer parentheses from an expression. `"($a + $b)"` → `"$a + $b"`, but `"foo($x)"` is left unchanged because the parens are part of the call syntax, not a redundant wrapper.

(s: &str)

/// `"($a + $b)"` → `"$a + $b"`, but `"foo($x)"` is left unchanged
/// because the parens are part of the call syntax, not a redundant wrapper.
fn strip_outer_parens(s: &str) -> &str {
    let bytes = s.as_bytes();
    if bytes.len() < 2 || bytes[0] != b'(' || bytes[bytes.len() - 1] != b')' {
        return s;
    }
    // Walk the interior and verify the opening '(' at position 0 is
    // the one that matches the closing ')' at the end.  If the depth
    // drops to zero before we reach the last character, the outer
    // parens are not a matched wrapper (e.g. `(a) + (b)`).
    let mut depth: u32 = 0;
    for (i, &b) in bytes.iter().enumerate() {
        match b {
            b'(' => depth += 1,
            b')' => {
                depth -= 1;
                if depth == 0 && i < bytes.len() - 1 {
                    // Closed before the final character — not an outer wrapper.
                    return s;
                }
            }
            _ => {}
        }
    }
    // The parens wrap the entire expression — strip them.
    s[1..s.len() - 1].trim()
}

/// Returns `true` when the selected text parses as a valid, self-contained
/// PHP expression.  We wrap it in `<?php $__x = <selection>;` and check