Reject removed runtime effects

Author: olwang

src/analyzer.rs

@@ -187,6 +187,26 @@ impl Analyzer<'_> {
 
             for effect in &function.effects {
                 let effect_name = effect_name(effect);
+                if let Some(replacement) = removed_runtime_effect_replacement(effect_name) {
+                    self.diagnostics.push(
+                        Diagnostic::error(
+                            code::REMOVED_RUNTIME_EFFECT,
+                            format!(
+                                "`{effect_name}` is not a valid RSScript v0.4.1 effect in `{}`.",
+                                function.name
+                            ),
+                            function.span.clone(),
+                            "removed runtime effect",
+                        )
+                        .with_cause("v0.4.1 uses reductive guarantees such as `no_panic`, `noalloc`, `no_block`, and `pure`.")
+                        .with_fix(
+                            "replace_removed_effect",
+                            replacement,
+                            "manual",
+                        ),
+                    );
+                    continue;
+                }
                 let valid = effect_name == "no_panic"
                     || effect_name == "noalloc"
                     || effect_name == "no_block"
@@ -660,6 +680,27 @@ fn effect_display(effect: &EffectDecl) -> String {
     }
 }
 
+fn removed_runtime_effect_replacement(effect_name: &str) -> Option<&'static str> {
+    match effect_name {
+        "io" => Some(
+            "Remove `io`; I/O is allowed by default unless a guarantee such as `pure` or `no_block` forbids it.",
+        ),
+        "allocates" => Some(
+            "Remove `allocates`; allocation is allowed by default. Use `noalloc` only when the function guarantees no allocation.",
+        ),
+        "may_panic" => Some(
+            "Remove `may_panic`; panic is allowed by default. Use `no_panic` only when the function guarantees no panic.",
+        ),
+        "may_fail" => Some(
+            "Remove `may_fail`; represent failure in the return type, for example `Result<T, E>`.",
+        ),
+        "async" => Some(
+            "Remove `async` from `effects(...)`; write `async fn` when the function itself is async.",
+        ),
+        _ => None,
+    }
+}
+
 fn duplicate_symbol_label(kind: DuplicateSymbolKind) -> &'static str {
     match kind {
         DuplicateSymbolKind::Function => "function",

src/diagnostic.rs

@@ -12,6 +12,7 @@ pub mod code {
     pub const INVALID_PURE_EFFECT: &str = "RS0009";
     pub const REMOVED_PROFILE_DECLARATION: &str = "RS0010";
     pub const REMOVED_SHARE_EFFECT: &str = "RS0011";
+    pub const REMOVED_RUNTIME_EFFECT: &str = "RS0012";
     pub const FILE_MODE_VIOLATION: &str = "RS0101";
     pub const UNNAMED_ARGUMENT: &str = "RS0201";
     pub const MISSING_DATA_EFFECT: &str = "RS0202";
@@ -255,6 +256,11 @@ static DIAGNOSTIC_EXPLANATIONS: &[DiagnosticExplanation] = &[
         title: "removed share data effect",
         explanation: "RSScript v0.4.1 removed `share` as a data effect. Retention must be declared with `effects(retains(param))`.",
     },
+    DiagnosticExplanation {
+        code: code::REMOVED_RUNTIME_EFFECT,
+        title: "removed runtime effect",
+        explanation: "RSScript v0.4.1 uses reductive guarantees. Additive runtime effects such as `io`, `allocates`, `may_panic`, and `may_fail` are not valid effects.",
+    },
     DiagnosticExplanation {
         code: code::FILE_MODE_VIOLATION,
         title: "file mode violation",

tests/fixtures/fail/removed-runtime-effects.rss

@@ -0,0 +1,12 @@
+// expect: RS0012
+mode: managed
+
+struct Image {
+    pixels: Buffer
+}
+
+fn load(path: read Path) -> Result<fresh Image, ImageError>
+    effects(io, allocates, may_panic, may_fail, async)
+{
+    return Image.load(path: read path)
+}