Add new label to E0283 #99308

obeis · 2022-07-16T02:17:33Z

Closes #98938

new label: `cannot call trait method as a free function`

to emit E0283

rust-highfive · 2022-07-16T02:17:36Z

r? @compiler-errors

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compiler-errors · 2022-07-16T02:26:51Z

Hi @obeis, thanks for the PR. Can you explain the approach you took here a bit more? Specifically:

How are we making sure to not say "cannot call trait method as a free function" on an expression like <_ as Trait>::method()?
What's the purpose of restricting to ObligationCauseCode::ItemObligation? Does this suppress erroneous suggestions you were seeing while testing?
Why are you checking param_env.is_const()? Same as above, does this suppress erroneous suggestions?

Please also provide a UI test or a few demonstrating your changes.

compiler-errors · 2022-07-16T02:37:32Z

LL |     let mut _q = Default::default();
   |                  ^^^^^^^^^^^^^^^^ cannot call trait method as a free function

The message is a bit confusing in this context. The problem here is not that we can't call Default::default as a free method, but instead that we're not able to infer the return type of Default::default.

If we are going to suggest this message, we may need to restrict it to function signatures that do not contain the ambiguous inference variable in either its inputs or outputs.

obeis · 2022-07-16T14:21:47Z

Hi @compiler-errors, thanks for taking time to review this.

On an expression like <_ as Trait>::method() the error emit with the new label so this need a fix.
Restricting to ObligationCauseCode::ItemObligation because this suppress erroneous suggestions i was seeing while testing.
Checking param_env.is_const() to suppress erroneous suggestions, like:

error[E0283]: type annotations needed
  --> /home/obei/rust/rust/src/test/ui/associated-consts/issue-63496.rs:4:21
   |
LL |     fn f() -> ([u8; A::C], [u8; A::C]);
   |                     ^^^^ cannot call trait method as a free function

error[E0283]: type annotations needed
  --> /home/obei/rust/rust/src/test/ui/associated-consts/issue-63496.rs:4:33
   |
LL |     fn f() -> ([u8; A::C], [u8; A::C]);
   |                                 ^^^^ cannot call trait method as a free function

ui test code, stderr for code

…ession like `<_ as Trait>::method()`

label: `cannot call trait method as a free function`

obeis · 2022-07-19T00:54:01Z

@rustbot ready
@compiler-errors Please have a look

bors · 2022-07-19T17:18:51Z

☔ The latest upstream changes (presumably #99462) made this pull request unmergeable. Please resolve the merge conflicts.

cjgillot · 2022-07-19T17:52:44Z

src/test/ui/error-codes/E0283.stderr

-   |
-LL |     let bar = <Impl as Into<T>>::into(foo_impl) * 1u32;
-   |               ++++++++++++++++++++++++        ~
+   |                        ^^^^ cannot call trait method as a free function


This note is wrong.

rust-log-analyzer · 2022-07-19T17:57:08Z

The job x86_64-gnu-llvm-12 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)


---- [ui] src/test/ui/associated-types/associated-types-unconstrained.rs stdout ----
diff of stderr:

- error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
3    |
- LL |     fn bar() -> isize;
-    |     ------------------ `Foo::bar` defined here
- ...
- ...
7 LL |     let x: isize = Foo::bar();
8    |                    ^^^^^^^^ cannot call trait method as a free function

10 error: aborting due to previous error
11 
- For more information about this error, try `rustc --explain E0790`.
---

error: 1 errors occurred comparing output.
Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/associated-types/associated-types-unconstrained.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/associated-types/associated-types-unconstrained" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/associated-types/associated-types-unconstrained/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/src/test/ui/associated-types/associated-types-unconstrained.rs:14:20
   |
LL |     let x: isize = Foo::bar();
LL |     let x: isize = Foo::bar();
   |                    ^^^^^^^^ cannot call trait method as a free function
error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.
------------------------------------------
------------------------------------------


---- [ui] src/test/ui/error-codes/E0283.rs stdout ----
diff of stderr:

- error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
2   --> $DIR/E0283.rs:30:21
- LL |     fn create() -> u32;
-    |     ------------------- `Generator::create` defined here
- ...
- ...
7 LL |     let cont: u32 = Generator::create();
8    |                     ^^^^^^^^^^^^^^^^^ cannot call trait method as a free function

15 
16 error: aborting due to 2 previous errors
17 
---
To only update this specific test, also pass `--test-args error-codes/E0283.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/error-codes/E0283.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/error-codes/E0283" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/error-codes/E0283/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/src/test/ui/error-codes/E0283.rs:30:21
   |
   |
LL |     let cont: u32 = Generator::create(); //~ ERROR E0790
   |                     ^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
error[E0283]: type annotations needed
  --> /checkout/src/test/ui/error-codes/E0283.rs:35:24
   |
   |
LL |     let bar = foo_impl.into() * 1u32; //~ ERROR E0283
   |                        ^^^^ cannot call trait method as a free function
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0283`.
------------------------------------------
------------------------------------------


---- [ui] src/test/ui/error-codes/E0790.rs stdout ----
diff of stderr:

- error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
2   --> $DIR/E0790.rs:17:9
3    |
- LL |         fn my_fn();
-    |         ----------- `MyTrait::my_fn` defined here
- ...
7 LL |         MyTrait::my_fn();
-    |         ^^^^^^^^^^^^^^ cannot call associated function of trait
- help: use the fully-qualified path to the only available implementation
-    |
-    |
- LL |         <::inner::MyStruct as MyTrait>::my_fn();
-    |         +++++++++++++++++++++        +
+    |         ^^^^^^^^^^^^^^ cannot call trait method as a free function
14 
- error[E0790]: cannot refer to the associated constant on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
16   --> $DIR/E0790.rs:21:17
17    |
- LL |         const MY_ASSOC_CONST: ();
-    |         ------------------------- `MyTrait::MY_ASSOC_CONST` defined here
- ...
21 LL |         let _ = MyTrait::MY_ASSOC_CONST;
-    |
- help: use the fully-qualified path to the only available implementation
-    |
-    |
- LL |         let _ = <::inner::MyStruct as MyTrait>::MY_ASSOC_CONST;
-    |                 +++++++++++++++++++++        +
+    |                 ^^^^^^^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
28 
- error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
30   --> $DIR/E0790.rs:26:5
31    |
- LL |         fn my_fn();
-    |         ----------- `MyTrait::my_fn` defined here
- ...
35 LL |     inner::MyTrait::my_fn();
-    |     ^^^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait
- help: use the fully-qualified path to the only available implementation
-    |
-    |
- LL |     inner::<::inner::MyStruct as MyTrait>::my_fn();
-    |            +++++++++++++++++++++        +
+    |     ^^^^^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
42 
- error[E0790]: cannot refer to the associated constant on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
44   --> $DIR/E0790.rs:30:13
45    |
- LL |         const MY_ASSOC_CONST: ();
-    |         ------------------------- `MyTrait::MY_ASSOC_CONST` defined here
- ...
49 LL |     let _ = inner::MyTrait::MY_ASSOC_CONST;
-    |
- help: use the fully-qualified path to the only available implementation
-    |
-    |
- LL |     let _ = inner::<::inner::MyStruct as MyTrait>::MY_ASSOC_CONST;
-    |                    +++++++++++++++++++++        +
+    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
56 
- error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
58   --> $DIR/E0790.rs:50:5
59    |
- LL |     fn my_fn();
-    |     ----------- `MyTrait2::my_fn` defined here
- ...
63 LL |     MyTrait2::my_fn();
-    |     ^^^^^^^^^^^^^^^ cannot call associated function of trait
-    |
- help: use a fully-qualified path to a specific available implementation (2 found)
-    |
- LL |     <::Impl1 as MyTrait2>::my_fn();
-    |     +++++++++++         +
+    |     ^^^^^^^^^^^^^^^ cannot call trait method as a free function
71 error: aborting due to 5 previous errors
72 

- For more information about this error, try `rustc --explain E0790`.
---
To only update this specific test, also pass `--test-args error-codes/E0790.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/error-codes/E0790.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/error-codes/E0790" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/error-codes/E0790/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/src/test/ui/error-codes/E0790.rs:17:9
   |
   |
LL |         MyTrait::my_fn(); //~ ERROR E0790
   |         ^^^^^^^^^^^^^^ cannot call trait method as a free function
error[E0283]: type annotations needed
  --> /checkout/src/test/ui/error-codes/E0790.rs:21:17
   |
   |
LL |         let _ = MyTrait::MY_ASSOC_CONST; //~ ERROR E0790
   |                 ^^^^^^^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
error[E0283]: type annotations needed
  --> /checkout/src/test/ui/error-codes/E0790.rs:26:5
   |
   |
LL |     inner::MyTrait::my_fn(); //~ ERROR E0790
   |     ^^^^^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
error[E0283]: type annotations needed
  --> /checkout/src/test/ui/error-codes/E0790.rs:30:13
   |
   |
LL |     let _ = inner::MyTrait::MY_ASSOC_CONST; //~ ERROR E0790
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
error[E0283]: type annotations needed
  --> /checkout/src/test/ui/error-codes/E0790.rs:50:5
   |
   |
LL |     MyTrait2::my_fn(); //~ ERROR E0790
   |     ^^^^^^^^^^^^^^^ cannot call trait method as a free function
error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0283`.
------------------------------------------
------------------------------------------


---- [ui] src/test/ui/traits/static-method-generic-inference.rs stdout ----
diff of stderr:

- error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+ error[E0283]: type annotations needed
3    |
- LL |         fn new() -> T;
- LL |         fn new() -> T;
-    |         -------------- `HasNew::new` defined here
- ...
7 LL |     let _f: base::Foo = base::HasNew::new();
8    |                         ^^^^^^^^^^^^^^^^^ cannot call trait method as a free function

10 error: aborting due to previous error
11 
- For more information about this error, try `rustc --explain E0790`.
---
To only update this specific test, also pass `--test-args traits/static-method-generic-inference.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/traits/static-method-generic-inference.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/traits/static-method-generic-inference" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/traits/static-method-generic-inference/auxiliary"
stdout: none
--- stderr -------------------------------
  --> /checkout/src/test/ui/traits/static-method-generic-inference.rs:24:25
   |
   |
LL |     let _f: base::Foo = base::HasNew::new();
   |                         ^^^^^^^^^^^^^^^^^ cannot call trait method as a free function
error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.
------------------------------------------

obeis added 3 commits July 16, 2022 04:35

Add new label for E0283

400b6d6

new label: `cannot call trait method as a free function`

Check if PredicateObligation is ObligationCauseCode::ItemObligation

29c32a8

to emit E0283

PredicateObligation should not be a constant to emit E0283

6c63d81

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jul 16, 2022

rust-highfive assigned compiler-errors Jul 16, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 16, 2022

compiler-errors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 16, 2022

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obeis added 3 commits July 18, 2022 21:43

Avoid saying cannot call trait method as a free function on an expr…

8f2c21d

…ession like `<_ as Trait>::method()`

Update ui test for the new E0283 label

afaa329

label: `cannot call trait method as a free function`

Add ui test for rust-lang#98938

c30bada

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 19, 2022

Merge branch 'master' into issue-98938

4ba1722

cjgillot reviewed Jul 19, 2022

View reviewed changes

compiler-errors mentioned this pull request Jul 19, 2022

Calling a trait method as a free function yields odd diagnostics #98938

Closed

obeis closed this Jul 19, 2022

obeis deleted the issue-98938 branch May 13, 2023 12:32

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Add new label to E0283 #99308

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