Don't discard attributed items when a proc-macro unexpectedly fails to expand

Author: Veykril

crates/hir_expand/src/proc_macro.rs

@@ -1,9 +1,10 @@
 //! Proc Macro Expander stub
 
-use crate::db::AstDatabase;
-use base_db::{CrateId, ProcMacroExpansionError, ProcMacroId};
+use base_db::{CrateId, ProcMacroExpansionError, ProcMacroId, ProcMacroKind};
 use mbe::ExpandResult;
 
+use crate::db::AstDatabase;
+
 #[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
 pub struct ProcMacroExpander {
     krate: CrateId,
@@ -36,20 +37,26 @@ impl ProcMacroExpander {
                 let krate_graph = db.crate_graph();
                 let proc_macro = match krate_graph[self.krate].proc_macro.get(id.0 as usize) {
                     Some(proc_macro) => proc_macro,
-                    None => return ExpandResult::str_err("No derive macro found.".to_string()),
+                    None => return ExpandResult::str_err("No proc-macro found.".to_string()),
                 };
 
                 // Proc macros have access to the environment variables of the invoking crate.
                 let env = &krate_graph[calling_crate].env;
-
-                proc_macro
-                    .expander
-                    .expand(tt, attr_arg, env)
-                    .map_err(|err| match err {
-                        ProcMacroExpansionError::Panic(text) => mbe::ExpandError::Other(text),
-                        ProcMacroExpansionError::System(text) => mbe::ExpandError::Other(text),
-                    })
-                    .into()
+                proc_macro.expander.expand(tt, attr_arg, env).map_or_else(
+                    |err| ExpandResult {
+                        // Don't discard the item in case something unexpected happened while expanding attributes
+                        value: if proc_macro.kind == ProcMacroKind::Attr {
+                            tt.clone()
+                        } else {
+                            Default::default()
+                        },
+                        err: Some(match err {
+                            ProcMacroExpansionError::Panic(text) => mbe::ExpandError::Other(text),
+                            ProcMacroExpansionError::System(text) => mbe::ExpandError::Other(text),
+                        }),
+                    },
+                    ExpandResult::ok,
+                )
             }
             None => ExpandResult::only_err(mbe::ExpandError::UnresolvedProcMacro),
         }