salsa-macros: handle invalid inputs in a way friendlier to rust-analyzer

components/salsa-macros/src/accumulator.rs

@@ -3,6 +3,7 @@ use proc_macro2::TokenStream;
 use crate::{
     hygiene::Hygiene,
     options::{AllowedOptions, Options},
+    token_stream_with_error,
 };
 
 // #[salsa::accumulator(jar = Jar0)]
@@ -14,7 +15,7 @@ pub(crate) fn accumulator(
 ) -> proc_macro::TokenStream {
     let hygiene = Hygiene::from1(&input);
     let args = syn::parse_macro_input!(args as Options<Accumulator>);
-    let struct_item = syn::parse_macro_input!(input as syn::ItemStruct);
+    let struct_item = parse_macro_input!(input as syn::ItemStruct);
     let ident = struct_item.ident.clone();
     let m = StructMacro {
         hygiene,
@@ -23,7 +24,7 @@ pub(crate) fn accumulator(
     };
     match m.try_expand() {
         Ok(v) => crate::debug::dump_tokens(ident, v).into(),
-        Err(e) => e.to_compile_error().into(),
+        Err(e) => token_stream_with_error(input, e),
     }
 }
 

components/salsa-macros/src/db.rs

@@ -1,7 +1,7 @@
 use proc_macro2::TokenStream;
 use syn::parse::Nothing;
 
-use crate::hygiene::Hygiene;
+use crate::{hygiene::Hygiene, token_stream_with_error};
 
 // Source:
 //
@@ -16,11 +16,11 @@ pub(crate) fn db(
 ) -> proc_macro::TokenStream {
     let _nothing = syn::parse_macro_input!(args as Nothing);
     let hygiene = Hygiene::from1(&input);
-    let input = syn::parse_macro_input!(input as syn::Item);
+    let item = parse_macro_input!(input as syn::Item);
     let db_macro = DbMacro { hygiene };
-    match db_macro.try_db(input) {
+    match db_macro.try_db(item) {
         Ok(v) => crate::debug::dump_tokens("db", v).into(),
-        Err(e) => e.to_compile_error().into(),
+        Err(e) => token_stream_with_error(input, e),
     }
 }
 

components/salsa-macros/src/input.rs

@@ -2,6 +2,7 @@ use crate::{
     hygiene::Hygiene,
     options::Options,
     salsa_struct::{SalsaStruct, SalsaStructAllowedOptions},
+    token_stream_with_error,
 };
 use proc_macro2::TokenStream;
 
@@ -16,15 +17,15 @@ pub(crate) fn input(
 ) -> proc_macro::TokenStream {
     let args = syn::parse_macro_input!(args as InputArgs);
     let hygiene = Hygiene::from1(&input);
-    let struct_item = syn::parse_macro_input!(input as syn::ItemStruct);
+    let struct_item = parse_macro_input!(input as syn::ItemStruct);
     let m = Macro {
         hygiene,
         args,
         struct_item,
     };
     match m.try_macro() {
         Ok(v) => v.into(),
-        Err(e) => e.to_compile_error().into(),
+        Err(e) => token_stream_with_error(input, e),
     }
 }
 

components/salsa-macros/src/interned.rs

@@ -3,6 +3,7 @@ use crate::{
     hygiene::Hygiene,
     options::Options,
     salsa_struct::{SalsaStruct, SalsaStructAllowedOptions},
+    token_stream_with_error,
 };
 use proc_macro2::TokenStream;
 
@@ -17,15 +18,15 @@ pub(crate) fn interned(
 ) -> proc_macro::TokenStream {
     let args = syn::parse_macro_input!(args as InternedArgs);
     let hygiene = Hygiene::from1(&input);
-    let struct_item = syn::parse_macro_input!(input as syn::ItemStruct);
+    let struct_item = parse_macro_input!(input as syn::ItemStruct);
     let m = Macro {
         hygiene,
         args,
         struct_item,
     };
     match m.try_macro() {
         Ok(v) => v.into(),
-        Err(e) => e.to_compile_error().into(),
+        Err(e) => token_stream_with_error(input, e),
     }
 }
 

components/salsa-macros/src/lib.rs

@@ -20,6 +20,20 @@ macro_rules! parse_quote {
     }
 }
 
+/// Similar to `syn::parse_macro_input`, however, when a parse error is encountered, it will return
+/// the input token stream in addition to the error. This will make it so that rust-analyzer can work
+/// with incomplete code.
+macro_rules! parse_macro_input {
+    ($tokenstream:ident as $ty:ty) => {
+        match syn::parse::<$ty>($tokenstream.clone()) {
+            Ok(data) => data,
+            Err(err) => {
+                return $crate::token_stream_with_error($tokenstream, err);
+            }
+        }
+    };
+}
+
 mod accumulator;
 mod db;
 mod db_lifetime;
@@ -64,9 +78,14 @@ pub fn tracked(args: TokenStream, input: TokenStream) -> TokenStream {
 
 #[proc_macro_derive(Update)]
 pub fn update(input: TokenStream) -> TokenStream {
-    let item = syn::parse_macro_input!(input as syn::DeriveInput);
+    let item = parse_macro_input!(input as syn::DeriveInput);
     match update::update_derive(item) {
         Ok(tokens) => tokens.into(),
-        Err(err) => err.to_compile_error().into(),
+        Err(error) => token_stream_with_error(input, error),
     }
 }
+
+pub(crate) fn token_stream_with_error(mut tokens: TokenStream, error: syn::Error) -> TokenStream {
+    tokens.extend(TokenStream::from(error.into_compile_error()));
+    tokens
+}

components/salsa-macros/src/tracked.rs

@@ -1,10 +1,12 @@
 use syn::{spanned::Spanned, Item};
 
+use crate::token_stream_with_error;
+
 pub(crate) fn tracked(
     args: proc_macro::TokenStream,
     input: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
-    let item = syn::parse_macro_input!(input as Item);
+    let item = parse_macro_input!(input as Item);
     let res = match item {
         syn::Item::Struct(item) => crate::tracked_struct::tracked_struct(args, item),
         syn::Item::Fn(item) => crate::tracked_fn::tracked_fn(args, item),
@@ -16,6 +18,6 @@ pub(crate) fn tracked(
     };
     match res {
         Ok(s) => s.into(),
-        Err(err) => err.into_compile_error().into(),
+        Err(err) => token_stream_with_error(input, err),
     }
 }

tests/compile-fail/input_struct_incompatibles.stderr

@@ -40,3 +40,9 @@ error: `#[id]` cannot be used with `#[salsa::input]`
 21 | /     #[id]
 22 | |     field: u32,
    | |______________^
+
+error: cannot find attribute `id` in this scope
+  --> tests/compile-fail/input_struct_incompatibles.rs:21:7
+   |
+21 |     #[id]
+   |       ^^

tests/compile-fail/interned_struct_incompatibles.stderr

@@ -40,3 +40,9 @@ error: `#[id]` cannot be used with `#[salsa::interned]`
 33 | /     #[id]
 34 | |     field: u32,
    | |______________^
+
+error: cannot find attribute `id` in this scope
+  --> tests/compile-fail/interned_struct_incompatibles.rs:33:7
+   |
+33 |     #[id]
+   |       ^^

tests/compile-fail/tracked_fn_incompatibles.stderr

@@ -46,6 +46,20 @@ error: only a single lifetime parameter is accepted
 67 | fn tracked_fn_with_multiple_lts<'db1, 'db2>(db: &'db1 dyn Db, interned: MyInterned<'db2>) -> u32 {
    |                                       ^^^^
 
+error: `self` parameter is only allowed in associated functions
+  --> tests/compile-fail/tracked_fn_incompatibles.rs:27:55
+   |
+27 | fn tracked_fn_with_receiver_not_applied_to_impl_block(&self, db: &dyn Db) -> u32 {}
+   |                                                       ^^^^^ not semantically valid as function parameter
+   |
+   = note: associated functions are those in `impl` or `trait` definitions
+
+error[E0415]: identifier `input` is bound more than once in this parameter list
+  --> tests/compile-fail/tracked_fn_incompatibles.rs:33:5
+   |
+33 |     input: MyInput,
+   |     ^^^^^ used as parameter more than once
+
 error[E0106]: missing lifetime specifier
   --> tests/compile-fail/tracked_fn_incompatibles.rs:61:15
    |
@@ -64,3 +78,20 @@ error[E0308]: mismatched types
    | ----------------- implicitly returns `()` as its body has no tail or `return` expression
 24 | fn tracked_fn_with_one_input(db: &dyn Db) -> u32 {}
    |                                              ^^^ expected `u32`, found `()`
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_fn_incompatibles.rs:27:78
+   |
+27 | fn tracked_fn_with_receiver_not_applied_to_impl_block(&self, db: &dyn Db) -> u32 {}
+   |    --------------------------------------------------                        ^^^ expected `u32`, found `()`
+   |    |
+   |    implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_fn_incompatibles.rs:34:6
+   |
+30 | fn tracked_fn_with_too_many_arguments_for_specify(
+   |    ---------------------------------------------- implicitly returns `()` as its body has no tail or `return` expression
+...
+34 | ) -> u32 {
+   |      ^^^ expected `u32`, found `()`

tests/compile-fail/tracked_impl_incompatibles.stderr

@@ -46,6 +46,69 @@ error: unexpected token
 41 | #[salsa::tracked(constructor = Constructor)]
    |                  ^^^^^^^^^^^
 
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:12:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+12 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:17:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+17 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:22:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+22 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:27:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+27 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:32:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+32 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:37:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+37 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
+error[E0119]: conflicting implementations of trait `Default` for type `MyTracked<'_>`
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:42:1
+   |
+7  | impl<'db> std::default::Default for MyTracked<'db> {
+   | -------------------------------------------------- first implementation here
+...
+42 | impl<'db> std::default::Default for MyTracked<'db> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `MyTracked<'_>`
+
 error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
   --> tests/compile-fail/tracked_impl_incompatibles.rs:47:1
    |
@@ -57,6 +120,70 @@ error[E0117]: only traits defined in the current crate can be implemented for ar
    |
    = note: define and implement a trait or new type instead
 
+error[E0308]: mismatched types
+ --> tests/compile-fail/tracked_impl_incompatibles.rs:8:21
+  |
+8 |     fn default() -> Self {}
+  |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+  |        |
+  |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:13:21
+   |
+13 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:18:21
+   |
+18 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:23:21
+   |
+23 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:28:21
+   |
+28 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:33:21
+   |
+33 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:38:21
+   |
+38 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
+error[E0308]: mismatched types
+  --> tests/compile-fail/tracked_impl_incompatibles.rs:43:21
+   |
+43 |     fn default() -> Self {}
+   |        -------      ^^^^ expected `MyTracked<'_>`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+
 error[E0308]: mismatched types
   --> tests/compile-fail/tracked_impl_incompatibles.rs:48:21
    |