fix: use Name.appendCore instead of Name.append in unresolveNameGlobal

src/Init/Prelude.lean

@@ -4335,8 +4335,13 @@ def addMacroScope (mainModule : Name) (n : Name) (scp : MacroScope) : Name :=
     Name.mkNum (Name.mkStr (Name.appendCore (Name.mkStr n "_@") mainModule) "_hyg") scp
 
 /--
-Append two names that may have macro scopes. The macro scopes in `b` are always erased.
-If `a` has macro scopes, then they are propagated to the result of `append a b`.
+Appends two names `a` and `b`, propagating macro scopes from `a` or `b`, if any, to the result.
+Panics if both `a` and `b` have macro scopes.
+
+This function is used for the `Append Name` instance.
+
+See also `Lean.Name.appendCore`, which appends names without any consideration for macro scopes.
+Also consider `Lean.Name.eraseMacroScopes` to erase macro scopes before appending, if appropriate.
 -/
 def Name.append (a b : Name) : Name :=
   match a.hasMacroScopes, b.hasMacroScopes with

src/Lean/ResolveName.lean

@@ -404,7 +404,7 @@ where
     for _ in [:revComponents.length] do
       match revComponents with
       | [] => return none
-      | cmpt::rest => candidate := cmpt ++ candidate; revComponents := rest
+      | cmpt::rest => candidate := Name.appendCore cmpt candidate; revComponents := rest
       match (← resolveGlobalName candidate) with
       | [(potentialMatch, _)] => if potentialMatch == n₀ then return some candidate else continue
       | _ => continue

tests/lean/run/2291.lean

@@ -0,0 +1,8 @@
+/-!
+Issue #2291
+
+The following example would cause the pretty printer to panic.
+-/
+
+set_option trace.compiler.simp true in
+#eval [0]