Improve span of maybe_update dummy implementation for better diagnostics

Author: MichaReiser

components/salsa-macro-rules/src/setup_tracked_fn.rs

@@ -55,6 +55,8 @@ macro_rules! setup_tracked_fn {
         // True if we `return_ref` flag was given to the function
         return_ref: $return_ref:tt,
 
+        maybe_update_fn: {$($maybe_update_fn:tt)*},
+
         // Annoyingly macro-rules hygiene does not extend to items defined in the macro.
         // We have the procedural macro generate names for those items that are
         // not used elsewhere in the user's code.
@@ -150,14 +152,8 @@ macro_rules! setup_tracked_fn {
             ///
             /// # Safety
             /// The same safety rules as for `Update` apply.
-            unsafe fn _implements_update<'db>(old_pointer: *mut $output_ty, new_value: $output_ty) -> bool {
-                unsafe {
-                    use $zalsa::UpdateFallback;
-                    $zalsa::UpdateDispatch::<$output_ty>::maybe_update(
-                        old_pointer, new_value
-                    )
-                }
-            }
+            $($maybe_update_fn)*
+
 
             impl $zalsa::function::Configuration for $Configuration {
                 const DEBUG_NAME: &'static str = stringify!($fn_name);

components/salsa-macros/src/tracked_fn.rs

@@ -117,6 +117,18 @@ impl Macro {
 
         let return_ref: bool = self.args.return_ref.is_some();
 
+        let maybe_update_fn = quote_spanned! {output_ty.span()=> {
+            #[allow(clippy::all, unsafe_code)]
+            unsafe fn _maybe_update_fn<'db>(old_pointer: *mut #output_ty, new_value: #output_ty) -> bool {
+                unsafe {
+                    use #zalsa::UpdateFallback;
+                    #zalsa::UpdateDispatch::<#output_ty>::maybe_update(
+                        old_pointer, new_value
+                    )
+                }
+            }
+        }};
+
         Ok(crate::debug::dump_tokens(
             fn_name,
             quote![salsa::plumbing::setup_tracked_fn! {
@@ -137,6 +149,7 @@ impl Macro {
                 needs_interner: #needs_interner,
                 lru: #lru,
                 return_ref: #return_ref,
+                maybe_update_fn: { #maybe_update_fn },
                 unused_names: [
                     #zalsa,
                     #Configuration,

tests/compile-fail/tracked_fn_return_ref.rs

@@ -1,5 +1,4 @@
 use salsa::Database as Db;
-use salsa::Update;
 
 #[salsa::input]
 struct MyInput {

tests/compile-fail/tracked_fn_return_ref.stderr

@@ -1,29 +1,20 @@
-warning: unused import: `salsa::Update`
- --> tests/compile-fail/tracked_fn_return_ref.rs:2:5
-  |
-2 | use salsa::Update;
-  |     ^^^^^^^^^^^^^
-  |
-  = note: `#[warn(unused_imports)]` on by default
-
 error: lifetime may not live long enough
-  --> tests/compile-fail/tracked_fn_return_ref.rs:15:1
+  --> tests/compile-fail/tracked_fn_return_ref.rs:14:1
    |
-15 | #[salsa::tracked]
-   | ^^^^^^^^^^^^^^^^^
-   | |
-   | lifetime `'db` defined here
-   | requires that `'db` must outlive `'static`
+14 | #[salsa::tracked]
+   | ^^^^^^^^^^^^^^^^^ requires that `'db` must outlive `'static`
+15 | fn tracked_fn_return_ref<'db>(db: &'db dyn Db, input: MyInput) -> &'db str {
+   |                                                                   - lifetime `'db` defined here
    |
-   = note: this error originates in the macro `salsa::plumbing::setup_tracked_fn` which comes from the expansion of the attribute macro `salsa::tracked` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the attribute macro `salsa::tracked` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: lifetime may not live long enough
-  --> tests/compile-fail/tracked_fn_return_ref.rs:20:1
+  --> tests/compile-fail/tracked_fn_return_ref.rs:19:1
    |
-20 | #[salsa::tracked]
-   | ^^^^^^^^^^^^^^^^^
-   | |
-   | lifetime `'db` defined here
-   | requires that `'db` must outlive `'static`
+19 | #[salsa::tracked]
+   | ^^^^^^^^^^^^^^^^^ requires that `'db` must outlive `'static`
+...
+23 | ) -> ContainsRef<'db> {
+   |      ----------- lifetime `'db` defined here
    |
-   = note: this error originates in the macro `salsa::plumbing::setup_tracked_fn` which comes from the expansion of the attribute macro `salsa::tracked` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the attribute macro `salsa::tracked` (in Nightly builds, run with -Z macro-backtrace for more info)