Factor out insert_or_error.

It appears identically as a closure in two functions.

Also change its return type from `bool` to `Option<()>` so it can be
used with `?`.

Author: nnethercote

compiler/rustc_attr/src/builtin.rs

@@ -353,28 +353,28 @@ pub fn find_body_stability(
     body_stab
 }
 
+fn insert_or_error(sess: &Session, meta: &MetaItem, item: &mut Option<Symbol>) -> Option<()> {
+    if item.is_some() {
+        handle_errors(
+            &sess.parse_sess,
+            meta.span,
+            AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
+        );
+        None
+    } else if let Some(v) = meta.value_str() {
+        *item = Some(v);
+        Some(())
+    } else {
+        sess.emit_err(session_diagnostics::IncorrectMetaItem { span: meta.span });
+        None
+    }
+}
+
 /// Read the content of a `stable`/`rustc_const_stable` attribute, and return the feature name and
 /// its stability information.
 fn parse_stability(sess: &Session, attr: &Attribute) -> Option<(Symbol, StabilityLevel)> {
     let meta = attr.meta()?;
     let MetaItem { kind: MetaItemKind::List(ref metas), .. } = meta else { return None };
-    let insert_or_error = |meta: &MetaItem, item: &mut Option<Symbol>| {
-        if item.is_some() {
-            handle_errors(
-                &sess.parse_sess,
-                meta.span,
-                AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
-            );
-            return false;
-        }
-        if let Some(v) = meta.value_str() {
-            *item = Some(v);
-            true
-        } else {
-            sess.emit_err(session_diagnostics::IncorrectMetaItem { span: meta.span });
-            false
-        }
-    };
 
     let mut feature = None;
     let mut since = None;
@@ -389,16 +389,8 @@ fn parse_stability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabilit
         };
 
         match mi.name_or_empty() {
-            sym::feature => {
-                if !insert_or_error(mi, &mut feature) {
-                    return None;
-                }
-            }
-            sym::since => {
-                if !insert_or_error(mi, &mut since) {
-                    return None;
-                }
-            }
+            sym::feature => insert_or_error(sess, mi, &mut feature)?,
+            sym::since => insert_or_error(sess, mi, &mut since)?,
             _ => {
                 handle_errors(
                     &sess.parse_sess,
@@ -438,23 +430,6 @@ fn parse_stability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabilit
 fn parse_unstability(sess: &Session, attr: &Attribute) -> Option<(Symbol, StabilityLevel)> {
     let meta = attr.meta()?;
     let MetaItem { kind: MetaItemKind::List(ref metas), .. } = meta else { return None };
-    let insert_or_error = |meta: &MetaItem, item: &mut Option<Symbol>| {
-        if item.is_some() {
-            handle_errors(
-                &sess.parse_sess,
-                meta.span,
-                AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
-            );
-            return false;
-        }
-        if let Some(v) = meta.value_str() {
-            *item = Some(v);
-            true
-        } else {
-            sess.emit_err(session_diagnostics::IncorrectMetaItem { span: meta.span });
-            false
-        }
-    };
 
     let mut feature = None;
     let mut reason = None;
@@ -473,20 +448,10 @@ fn parse_unstability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabil
         };
 
         match mi.name_or_empty() {
-            sym::feature => {
-                if !insert_or_error(mi, &mut feature) {
-                    return None;
-                }
-            }
-            sym::reason => {
-                if !insert_or_error(mi, &mut reason) {
-                    return None;
-                }
-            }
+            sym::feature => insert_or_error(sess, mi, &mut feature)?,
+            sym::reason => insert_or_error(sess, mi, &mut reason)?,
             sym::issue => {
-                if !insert_or_error(mi, &mut issue) {
-                    return None;
-                }
+                insert_or_error(sess, mi, &mut issue)?;
 
                 // These unwraps are safe because `insert_or_error` ensures the meta item
                 // is a name/value pair string literal.
@@ -515,11 +480,7 @@ fn parse_unstability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabil
                 }
                 is_soft = true;
             }
-            sym::implied_by => {
-                if !insert_or_error(mi, &mut implied_by) {
-                    return None;
-                }
-            }
+            sym::implied_by => insert_or_error(sess, mi, &mut implied_by)?,
             _ => {
                 handle_errors(
                     &sess.parse_sess,