Add note to error

external-crates/move/crates/move-compiler/src/naming/translate.rs

@@ -2517,24 +2517,28 @@ fn exp(context: &mut Context, e: Box<E::Exp>) -> Box<N::Exp> {
                     }
                     // If this variable refers to a local (num > 0) or it isn't syntax, error.
                     if !v.value.is_syntax_identifier() {
+                        let name = v.value.name;
                         let msg = format!(
-                            "Unexpected invocation of parameter or local '{}'. \
-                                     Non-syntax variables cannot be invoked as functions.",
-                            v.value.name
+                            "Unexpected invocation of parameter or local '{name}'. \
+                                     Non-syntax variables cannot be invoked as functions",
                         );
+                        let note = format!(
+                            "Only macro syntax variables, e.g. '${name}', \
+                            may be invoked as functions."
+                        );
+                        let mut diag = diag!(TypeSafety::InvalidCallTarget, (v.loc, msg));
+                        diag.add_note(note);
                         context
                             .env
-                            .add_diag(diag!(TypeSafety::InvalidCallTarget, (v.loc, msg)));
+                            .add_diag(diag);
                         NE::UnresolvedError
                     } else if v.value.id != 0 {
+                        let name = v.value.name;
                         let msg = format!(
-                            "Unexpected invocation of non-parameter variable '{}'. \
+                            "Unexpected invocation of non-parameter variable '{name}'. \
                                      Only lambda-typed syntax parameters may be invoked",
-                            v.value.name
                         );
-                        context
-                            .env
-                            .add_diag(diag!(TypeSafety::InvalidCallTarget, (v.loc, msg)));
+                        context.env.add_diag(diag!(TypeSafety::InvalidCallTarget, (v.loc, msg)));
                         NE::UnresolvedError
                     } else {
                         NE::VarCall(v, nes)

external-crates/move/crates/move-compiler/tests/move_2024/expansion/macro_identifier_missing.exp

@@ -32,5 +32,7 @@ error[E04029]: invalid function call
   ┌─ tests/move_2024/expansion/macro_identifier_missing.move:3:9
   │
 3 │         f(x)
-  │         ^ Unexpected invocation of parameter or local 'f'. Non-syntax variables cannot be invoked as functions.
+  │         ^ Unexpected invocation of parameter or local 'f'. Non-syntax variables cannot be invoked as functions
+  │
+  = Only macro syntax variables, e.g. '$f', may be invoked as functions.
 

external-crates/move/crates/move-compiler/tests/move_2024/naming/macro_parameter_assignment.exp

@@ -22,7 +22,9 @@ error[E04029]: invalid function call
   ┌─ tests/move_2024/naming/macro_parameter_assignment.move:5:9
   │
 5 │         f(x)
-  │         ^ Unexpected invocation of parameter or local 'f'. Non-syntax variables cannot be invoked as functions.
+  │         ^ Unexpected invocation of parameter or local 'f'. Non-syntax variables cannot be invoked as functions
+  │
+  = Only macro syntax variables, e.g. '$f', may be invoked as functions.
 
 warning[W09005]: dead or unreachable code
    ┌─ tests/move_2024/naming/macro_parameter_assignment.move:10:15

external-crates/move/crates/move-compiler/tests/move_2024/naming/var_as_fun_invalid.exp

@@ -2,5 +2,7 @@ error[E04029]: invalid function call
   ┌─ tests/move_2024/naming/var_as_fun_invalid.move:4:9
   │
 4 │         var();
-  │         ^^^ Unexpected invocation of parameter or local 'var'. Non-syntax variables cannot be invoked as functions.
+  │         ^^^ Unexpected invocation of parameter or local 'var'. Non-syntax variables cannot be invoked as functions
+  │
+  = Only macro syntax variables, e.g. '$var', may be invoked as functions.
 

external-crates/move/crates/move-compiler/tests/move_2024/typing/use_lambda_outside_call_invalid.exp

@@ -8,7 +8,9 @@ error[E04029]: invalid function call
   ┌─ tests/move_2024/typing/use_lambda_outside_call_invalid.move:4:9
   │
 4 │         x();
-  │         ^ Unexpected invocation of parameter or local 'x'. Non-syntax variables cannot be invoked as functions.
+  │         ^ Unexpected invocation of parameter or local 'x'. Non-syntax variables cannot be invoked as functions
+  │
+  = Only macro syntax variables, e.g. '$x', may be invoked as functions.
 
 error[E02010]: invalid name
   ┌─ tests/move_2024/typing/use_lambda_outside_call_invalid.move:7:23

external-crates/move/crates/move-compiler/tests/move_check/naming/var_as_fun_invalid.exp

@@ -2,7 +2,9 @@ error[E04029]: invalid function call
   ┌─ tests/move_check/naming/var_as_fun_invalid.move:4:9
   │
 4 │         var();
-  │         ^^^ Unexpected invocation of parameter or local 'var'. Non-syntax variables cannot be invoked as functions.
+  │         ^^^ Unexpected invocation of parameter or local 'var'. Non-syntax variables cannot be invoked as functions
+  │
+  = Only macro syntax variables, e.g. '$var', may be invoked as functions.
 
 error[E13001]: feature is not supported in specified edition
   ┌─ tests/move_check/naming/var_as_fun_invalid.move:4:9