feat(selfhost-checker): add RS0007 (unknown/copy retained parameter)

Corpus-green over 619 files: retains(p) flags when p is not a param or
is a Copy-scalar param.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: olwang

crates/rsscript/src/selfhost_parity.rs

@@ -503,7 +503,7 @@ fn parser_parity_corpus() {
 // ---------------------------------------------------------------------------
 
 /// Diagnostic codes the rss checker is expected to reproduce.
-const CHECKER_TARGET_CODES: &[&str] = &["RS0002","RS0003","RS0004","RS0005","RS0006","RS0010","RS0011","RS0012","RS0016","RS0017","RS0028","RS0033"];
+const CHECKER_TARGET_CODES: &[&str] = &["RS0002","RS0003","RS0004","RS0005","RS0006","RS0007","RS0010","RS0011","RS0012","RS0016","RS0017","RS0028","RS0033"];
 
 fn is_target_code(code: &str) -> bool {
     CHECKER_TARGET_CODES.contains(&code)

selfhost/check.rss

@@ -519,6 +519,119 @@ fn seg_is_share(toks: read List<Tok>, segStart: read Int, segEnd: read Int) -> B
     return tk_text(toks: read toks, i: read (segStart + 2)) == "share"
 }
 
+// The 17 Copy scalar type names (crate scalar/primitive set).
+fn is_scalar_name(name: read String) -> Bool {
+    return name == "Bool" || name == "Byte" || name == "Char" || name == "Float" || name == "Float32" || name == "Float64" || name == "Int" || name == "Int8" || name == "Int16" || name == "Int32" || name == "Int64" || name == "UInt" || name == "UInt8" || name == "UInt16" || name == "UInt32" || name == "UInt64" || name == "Unit"
+}
+
+// Copy classification of a param type region for RS0007. The type begins after
+// `name :` and an optional data-effect; then optional prefixes precede the base.
+// Copy iff (no fresh/noescape prefix) AND base ∈ scalars AND next token is not `<`.
+fn seg_type_is_copy(toks: read List<Tok>, segStart: read Int, segEnd: read Int) -> Bool {
+    let mut k = segStart + 2
+    if is_effect_kw(toks: read toks, i: read k) { k = k + 1 }
+    let mut sawFreshNoescape = false
+    let mut scanning = true
+    while scanning {
+        let t = tk_text(toks: read toks, i: read k)
+        if t == "fresh" || t == "noescape" {
+            sawFreshNoescape = true
+            k = k + 1
+        } else if t == "owned" || t == "handle" || t == "weak" {
+            k = k + 1
+        } else {
+            scanning = false
+        }
+    }
+    if sawFreshNoescape { return false }
+    let base = tk_text(toks: read toks, i: read k)
+    if is_scalar_name(name: read base) == false { return false }
+    if at_symbol(toks: read toks, i: read (k + 1), code: read SYM_LANGLE) { return false }
+    return true
+}
+
+// Status of a named param for RS0007: -1 = this segment is not param `pname`,
+// 2 = matched and Copy, 1 = matched and non-Copy.
+fn one_param_status(toks: read List<Tok>, segStart: read Int, segEnd: read Int, pname: read String) -> Int {
+    if segStart >= segEnd { return -1 }
+    if is_ident_tok(toks: read toks, i: read segStart) == false { return -1 }
+    if at_symbol(toks: read toks, i: read (segStart + 1), code: read SYM_COLON) == false { return -1 }
+    if tk_text(toks: read toks, i: read segStart) != pname { return -1 }
+    if seg_type_is_copy(toks: read toks, segStart: read segStart, segEnd: read segEnd) { return 2 }
+    return 1
+}
+
+// Walk the param list [open,close] looking for param `pname`. Returns 0 (not a
+// param), 1 (param, non-Copy), or 2 (param, Copy).
+fn param_retains_status(toks: read List<Tok>, open: read Int, close: read Int, pname: read String) -> Int {
+    let mut k = open + 1
+    let mut depth = 0
+    let mut angle = 0
+    let mut segStart = open + 1
+    let mut status = 0
+    while k < close {
+        let opener = at_symbol(toks: read toks, i: read k, code: read SYM_LPAREN) || at_symbol(toks: read toks, i: read k, code: read SYM_LBRACKET) || at_symbol(toks: read toks, i: read k, code: read SYM_LBRACE)
+        let closer = at_symbol(toks: read toks, i: read k, code: read SYM_RPAREN) || at_symbol(toks: read toks, i: read k, code: read SYM_RBRACKET) || at_symbol(toks: read toks, i: read k, code: read SYM_RBRACE)
+        if opener {
+            depth = depth + 1
+        } else if closer {
+            if depth > 0 { depth = depth - 1 }
+        } else if at_symbol(toks: read toks, i: read k, code: read SYM_LANGLE) {
+            angle = angle + 1
+        } else if at_symbol(toks: read toks, i: read k, code: read SYM_RANGLE) {
+            if angle > 0 { angle = angle - 1 }
+        } else if depth == 0 && angle == 0 && at_symbol(toks: read toks, i: read k, code: read SYM_COMMA) {
+            let s = one_param_status(toks: read toks, segStart: read segStart, segEnd: read k, pname: read pname)
+            if s != -1 { status = s }
+            segStart = k + 1
+        }
+        k = k + 1
+    }
+    let s = one_param_status(toks: read toks, segStart: read segStart, segEnd: read close, pname: read pname)
+    if s != -1 { status = s }
+    return status
+}
+
+// One effects-clause item [segStart,segEnd): a `retains(p)` where p is not a
+// param, or is a Copy param → RS0007.
+fn retains_item_bad(toks: read List<Tok>, segStart: read Int, segEnd: read Int, popen: read Int, pclose: read Int) -> Bool {
+    if effect_item_kind(toks: read toks, segStart: read segStart, segEnd: read segEnd) != 2 { return false }
+    let pname = tk_text(toks: read toks, i: read (segStart + 2))
+    let status = param_retains_status(toks: read toks, open: read popen, close: read pclose, pname: read pname)
+    return status == 0 || status == 2
+}
+
+// RS0007: an `effects(retains(p))` item whose p is not a param, or is a Copy param.
+fn fn_retains_bad(toks: read List<Tok>, start: read Int) -> Bool {
+    let effOpen = find_effects_open(toks: read toks, start: read start)
+    if effOpen < 0 { return false }
+    let effClose = find_matching(toks: read toks, open: read effOpen, openSym: read SYM_LPAREN, closeSym: read SYM_RPAREN)
+    if effClose < 0 { return false }
+    let ns = fn_name_start(toks: read toks, i: read start)
+    let sigEnd = function_signature_end(toks: read toks, start: read (ns - 1))
+    let popen = find_param_open(toks: read toks, from: read ns, end: read sigEnd)
+    if popen < 0 { return false }
+    let pclose = find_matching(toks: read toks, open: read popen, openSym: read SYM_LPAREN, closeSym: read SYM_RPAREN)
+    if pclose < 0 { return false }
+    let mut k = effOpen + 1
+    let mut segStart = effOpen + 1
+    let mut depth = 0
+    let mut hit = false
+    while k < effClose {
+        if at_symbol(toks: read toks, i: read k, code: read SYM_LPAREN) {
+            depth = depth + 1
+        } else if at_symbol(toks: read toks, i: read k, code: read SYM_RPAREN) {
+            if depth > 0 { depth = depth - 1 }
+        } else if depth == 0 && at_symbol(toks: read toks, i: read k, code: read SYM_COMMA) {
+            if retains_item_bad(toks: read toks, segStart: read segStart, segEnd: read k, popen: read popen, pclose: read pclose) { hit = true }
+            segStart = k + 1
+        }
+        k = k + 1
+    }
+    if retains_item_bad(toks: read toks, segStart: read segStart, segEnd: read effClose, popen: read popen, pclose: read pclose) { hit = true }
+    return hit
+}
+
 fn main() -> Unit {
     let source = Args.get_or_default(index: 0, default: read "")
     let toks = tokenize(source: read source)
@@ -541,6 +654,7 @@ fn main() -> Unit {
     let mut unknownEffect = false
     let mut removedRuntime = false
     let mut invalidSelf = false
+    let mut retainsBad = false
     // RS0033: any decimal integer literal in the file that overflows i64.
     let outOfRangeInt = has_out_of_range_int(toks: read toks)
     let mut i = 0
@@ -691,6 +805,7 @@ fn main() -> Unit {
                     if effects_name_probe(toks: read toks, start: read i, mode: read 0) { unknownEffect = true }
                     if effects_name_probe(toks: read toks, start: read i, mode: read 1) { removedRuntime = true }
                     if fn_has_invalid_self(toks: read toks, start: read i) { invalidSelf = true }
+                    if fn_retains_bad(toks: read toks, start: read i) { retainsBad = true }
                     i = r
                 }
             } else {
@@ -726,6 +841,9 @@ fn main() -> Unit {
     if invalidSelf {
         Log.write(message: read "RS0028")
     }
+    if retainsBad {
+        Log.write(message: read "RS0007")
+    }
     if outOfRangeInt {
         Log.write(message: read "RS0033")
     }
@@ -738,7 +856,7 @@ fn main() -> Unit {
     if headerCount >= 2 {
         Log.write(message: read "RS0006")
     }
-    let anyDiag = found || hasUnknownFeat || hasDupFeat || headerCount >= 2 || missingReturn || untypedParam || hasProfile || shareParam || unknownEffect || removedRuntime || invalidSelf || outOfRangeInt
+    let anyDiag = found || hasUnknownFeat || hasDupFeat || headerCount >= 2 || missingReturn || untypedParam || hasProfile || shareParam || unknownEffect || removedRuntime || invalidSelf || outOfRangeInt || retainsBad
     if anyDiag == false {
         Log.write(message: read "CLEAN")
     }