Clean up query macros for cache_on_disk_if

Zalathar · Zalathar · commit b2d5760eaeba · 2026-02-01T20:49:15.000+11:00
diff --git a/compiler/rustc_macros/src/query.rs b/compiler/rustc_macros/src/query.rs
@@ -90,7 +90,7 @@ struct QueryModifiers {
     arena_cache: Option<Ident>,
 
     /// Cache the query to disk if the `Block` returns true.
-    cache: Option<(Option<Pat>, Block)>,
+    cache_on_disk_if: Option<(Option<Pat>, Block)>,
 
     /// A cycle error for this query aborting the compilation with a fatal error.
     cycle_fatal: Option<Ident>,
@@ -134,7 +134,7 @@ struct QueryModifiers {
 
 fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
     let mut arena_cache = None;
-    let mut cache = None;
+    let mut cache_on_disk_if = None;
     let mut desc = None;
     let mut cycle_fatal = None;
     let mut cycle_delay_bug = None;
@@ -175,8 +175,11 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
             let list = attr_content.parse_terminated(Expr::parse, Token![,])?;
             try_insert!(desc = (tcx, list));
         } else if modifier == "cache_on_disk_if" {
-            // Parse a cache modifier like:
-            // `cache(tcx) { |tcx| key.is_local() }`
+            // Parse a cache-on-disk modifier like:
+            //
+            // `cache_on_disk_if { true }`
+            // `cache_on_disk_if { key.is_local() }`
+            // `cache_on_disk_if(tcx) { tcx.is_typeck_child(key.to_def_id()) }`
             let args = if input.peek(token::Paren) {
                 let args;
                 parenthesized!(args in input);
@@ -186,7 +189,7 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
                 None
             };
             let block = input.parse()?;
-            try_insert!(cache = (args, block));
+            try_insert!(cache_on_disk_if = (args, block));
         } else if modifier == "arena_cache" {
             try_insert!(arena_cache = modifier);
         } else if modifier == "cycle_fatal" {
@@ -218,7 +221,7 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
     };
     Ok(QueryModifiers {
         arena_cache,
-        cache,
+        cache_on_disk_if,
         desc,
         cycle_fatal,
         cycle_delay_bug,
@@ -260,12 +263,18 @@ fn doc_comment_from_desc(list: &Punctuated<Expr, token::Comma>) -> Result<Attrib
     Ok(parse_quote! { #[doc = #doc_string] })
 }
 
-/// Add the impl of QueryDescription for the query to `impls` if one is requested
-fn add_query_desc_cached_impl(
-    query: &Query,
-    descs: &mut proc_macro2::TokenStream,
-    cached: &mut proc_macro2::TokenStream,
-) {
+/// Contains token streams that are used to accumulate per-query helper
+/// functions, to be used by the final output of `rustc_queries!`.
+///
+/// Helper items typically have the same name as the query they relate to,
+/// and expect to be interpolated into a dedicated module.
+#[derive(Default)]
+struct HelperTokenStreams {
+    descs_stream: proc_macro2::TokenStream,
+    cache_on_disk_if_fns_stream: proc_macro2::TokenStream,
+}
+
+fn make_helpers_for_query(query: &Query, streams: &mut HelperTokenStreams) {
     let Query { name, key, modifiers, .. } = &query;
 
     // This dead code exists to instruct rust-analyzer about the link between the `rustc_queries`
@@ -281,12 +290,12 @@ fn add_query_desc_cached_impl(
     };
 
     // Generate a function to check whether we should cache the query to disk, for some key.
-    if let Some((args, expr)) = modifiers.cache.as_ref() {
+    if let Some((args, expr)) = modifiers.cache_on_disk_if.as_ref() {
         let tcx = args.as_ref().map(|t| quote! { #t }).unwrap_or_else(|| quote! { _ });
         // expr is a `Block`, meaning that `{ #expr }` gets expanded
         // to `{ { stmts... } }`, which triggers the `unused_braces` lint.
         // we're taking `key` by reference, but some rustc types usually prefer being passed by value
-        cached.extend(quote! {
+        streams.cache_on_disk_if_fns_stream.extend(quote! {
             #[allow(unused_variables, unused_braces, rustc::pass_by_value)]
             #[inline]
             pub fn #name<'tcx>(#tcx: TyCtxt<'tcx>, #key: &crate::query::queries::#name::Key<'tcx>) -> bool {
@@ -309,7 +318,7 @@ fn add_query_desc_cached_impl(
         }
     };
 
-    descs.extend(quote! {
+    streams.descs_stream.extend(quote! {
         #desc
     });
 }
@@ -318,8 +327,7 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {
     let queries = parse_macro_input!(input as List<Query>);
 
     let mut query_stream = quote! {};
-    let mut query_description_stream = quote! {};
-    let mut query_cached_stream = quote! {};
+    let mut helpers = HelperTokenStreams::default();
     let mut feedable_queries = quote! {};
     let mut errors = quote! {};
 
@@ -364,9 +372,11 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {
             return_result_from_ensure_ok,
         );
 
-        // Pass on the cache modifier
-        if modifiers.cache.is_some() {
-            attributes.push(quote! { (cache) });
+        // If there was a `cache_on_disk_if` modifier in the real input, pass
+        // on a synthetic `(cache_on_disk)` modifier that can be inspected by
+        // macro-rules macros.
+        if modifiers.cache_on_disk_if.is_some() {
+            attributes.push(quote! { (cache_on_disk) });
         }
 
         // This uses the span of the query definition for the commas,
@@ -400,9 +410,12 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {
             });
         }
 
-        add_query_desc_cached_impl(&query, &mut query_description_stream, &mut query_cached_stream);
+        make_helpers_for_query(&query, &mut helpers);
     }
 
+    let HelperTokenStreams { descs_stream: query_description_stream, cache_on_disk_if_fns_stream } =
+        helpers;
+
     TokenStream::from(quote! {
         /// Higher-order macro that invokes the specified macro with a prepared
         /// list of all query signatures (including modifiers).
@@ -434,10 +447,15 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {
             use super::*;
             #query_description_stream
         }
-        pub mod cached {
+
+        // FIXME(Zalathar): Instead of declaring these functions directly, can
+        // we put them in a macro and then expand that macro downstream in
+        // `rustc_query_impl`, where the functions are actually used?
+        pub mod _cache_on_disk_if_fns {
             use super::*;
-            #query_cached_stream
+            #cache_on_disk_if_fns_stream
         }
+
         #errors
     })
 }
diff --git a/compiler/rustc_query_impl/src/plumbing.rs b/compiler/rustc_query_impl/src/plumbing.rs
@@ -305,15 +305,31 @@ macro_rules! call_provider {
     };
 }
 
-macro_rules! should_ever_cache_on_disk {
-    ([]$yes:tt $no:tt) => {{
+/// Expands to one of two token trees, depending on whether the current query
+/// has the `cache_on_disk_if` modifier.
+macro_rules! if_cache_on_disk {
+    ([] $yes:tt $no:tt) => {
         $no
-    }};
-    ([(cache) $($rest:tt)*]$yes:tt $no:tt) => {{
+    };
+    // The `cache_on_disk_if` modifier generates a synthetic `(cache_on_disk)`,
+    // modifier, for use by this macro and similar macros.
+    ([(cache_on_disk) $($rest:tt)*] $yes:tt $no:tt) => {
         $yes
-    }};
-    ([$other:tt $($modifiers:tt)*]$yes:tt $no:tt) => {
-        should_ever_cache_on_disk!([$($modifiers)*]$yes $no)
+    };
+    ([$other:tt $($modifiers:tt)*] $yes:tt $no:tt) => {
+        if_cache_on_disk!([$($modifiers)*] $yes $no)
+    };
+}
+
+/// Conditionally expands to some token trees, if the current query has the
+/// `cache_on_disk_if` modifier.
+macro_rules! item_if_cache_on_disk {
+    ([] $($item:tt)*) => {};
+    ([(cache_on_disk) $($rest:tt)*] $($item:tt)*) => {
+        $($item)*
+    };
+    ([$other:tt $($modifiers:tt)*] $($item:tt)*) => {
+        item_if_cache_on_disk! { [$($modifiers)*] $($item)* }
     };
 }
 
@@ -546,28 +562,6 @@ where
     }
 }
 
-macro_rules! item_if_cached {
-    ([] $tokens:tt) => {};
-    ([(cache) $($rest:tt)*] { $($tokens:tt)* }) => {
-        $($tokens)*
-    };
-    ([$other:tt $($modifiers:tt)*] $tokens:tt) => {
-        item_if_cached! { [$($modifiers)*] $tokens }
-    };
-}
-
-macro_rules! expand_if_cached {
-    ([], $tokens:expr) => {{
-        None
-    }};
-    ([(cache) $($rest:tt)*], $tokens:expr) => {{
-        Some($tokens)
-    }};
-    ([$other:tt $($modifiers:tt)*], $tokens:expr) => {
-        expand_if_cached!([$($modifiers)*], $tokens)
-    };
-}
-
 /// Don't show the backtrace for query system by default
 /// use `RUST_BACKTRACE=full` to show all the backtraces
 #[inline(never)]
@@ -648,8 +642,8 @@ macro_rules! define_queries {
                     cycle_error_handling: cycle_error_handling!([$($modifiers)*]),
                     query_state: std::mem::offset_of!(QueryStates<'tcx>, $name),
                     query_cache: std::mem::offset_of!(QueryCaches<'tcx>, $name),
-                    will_cache_on_disk_for_key_fn: should_ever_cache_on_disk!([$($modifiers)*] {
-                        Some(::rustc_middle::query::cached::$name)
+                    will_cache_on_disk_for_key_fn: if_cache_on_disk!([$($modifiers)*] {
+                        Some(::rustc_middle::query::_cache_on_disk_if_fns::$name)
                     } {
                         None
                     }),
@@ -670,10 +664,10 @@ macro_rules! define_queries {
                             )
                         )
                     },
-                    try_load_from_disk_fn: should_ever_cache_on_disk!([$($modifiers)*] {
+                    try_load_from_disk_fn: if_cache_on_disk!([$($modifiers)*] {
                         Some(|tcx, key, prev_index, index| {
                             // Check the `cache_on_disk_if` condition for this key.
-                            if !::rustc_middle::query::cached::$name(tcx, key) {
+                            if !::rustc_middle::query::_cache_on_disk_if_fns::$name(tcx, key) {
                                 return None;
                             }
 
@@ -686,9 +680,9 @@ macro_rules! define_queries {
                     } {
                         None
                     }),
-                    is_loadable_from_disk_fn: should_ever_cache_on_disk!([$($modifiers)*] {
+                    is_loadable_from_disk_fn: if_cache_on_disk!([$($modifiers)*] {
                         Some(|tcx, key, index| -> bool {
-                            ::rustc_middle::query::cached::$name(tcx, key) &&
+                            ::rustc_middle::query::_cache_on_disk_if_fns::$name(tcx, key) &&
                                 $crate::plumbing::loadable_from_disk(tcx, index)
                         })
                     } {
@@ -773,7 +767,7 @@ macro_rules! define_queries {
                 )
             }
 
-            item_if_cached! { [$($modifiers)*] {
+            item_if_cache_on_disk! { [$($modifiers)*]
                 pub(crate) fn encode_query_results<'tcx>(
                     tcx: TyCtxt<'tcx>,
                     encoder: &mut CacheEncoder<'_, 'tcx>,
@@ -786,7 +780,7 @@ macro_rules! define_queries {
                         query_result_index,
                     )
                 }
-            }}
+            }
 
             pub(crate) fn query_key_hash_verify<'tcx>(tcx: TyCtxt<'tcx>) {
                 $crate::plumbing::query_key_hash_verify(
@@ -833,7 +827,15 @@ macro_rules! define_queries {
                 &mut CacheEncoder<'_, 'tcx>,
                 &mut EncodedDepNodeIndex)
             >
-        ] = &[$(expand_if_cached!([$($modifiers)*], query_impl::$name::encode_query_results)),*];
+        ] = &[
+            $(
+                if_cache_on_disk!([$($modifiers)*] {
+                    Some(query_impl::$name::encode_query_results)
+                } {
+                    None
+                })
+            ),*
+        ];
 
         const QUERY_KEY_HASH_VERIFY: &[
             for<'tcx> fn(TyCtxt<'tcx>)
