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const fn: Improve wording #59646

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merged 3 commits into from
Apr 17, 2019
Merged

const fn: Improve wording #59646

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ae2ed21
Improve wording
JohnTitor Apr 2, 2019
dce86f9
Make wording verbose
JohnTitor Apr 15, 2019
4075415
Fix tests
JohnTitor Apr 15, 2019
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2 changes: 1 addition & 1 deletion src/librustc_mir/transform/qualify_min_const_fn.rs
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Expand Up @@ -326,7 +326,7 @@ fn check_terminator(
abi::Abi::Rust if tcx.is_min_const_fn(def_id) => {},
abi::Abi::Rust => return Err((
span,
"can only call other `min_const_fn` within a `min_const_fn`".into(),
"can only call other `const` within a `const`".into(),
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Something like can only call another `const fn` within a `const` block sounds more natural.

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Neither this PR nor the suggestion is accurate. This is not a const block (and with rust-lang/rfcs#2632 it will not always behave in a similar fashion).

Moreover, I think we lose out on the difference between stable const fns and unstable ones. This is the main point of min_const_fns... I think we should check whether the current compiler can use unstable features and tweak the message based on that. E.g. a stable compiler can just talk about const fns but the nightly compiler should emphasize the difference between stable and unstable ones.

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Maybe change it to

can only call other stable `const fn` within a stable `const fn`

?

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Ah, in that case we should make the error more explicit and add a note to the unstable const fn pointing out that it is undertake.

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That is, it's not clear whether it's the containing function or the called function that is the problem (or both).

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The problem is to be used same wording without distinction, I think. Should we try to work on this?

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kinda both. I'm not sure how easy it is to point to the unstable const fn, since it might be in another crate. We can just use a more verbose wording like

can only call other const fn within a const fn, but insert_fn_name_here is not stable as const fn

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@oli-obk I changed wording.

)),
abi => return Err((
span,
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6 changes: 3 additions & 3 deletions src/test/ui/consts/min_const_fn/min_const_fn_libstd_stability.rs
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Expand Up @@ -12,14 +12,14 @@ const fn foo() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const fn bar() -> u32 { foo() } //~ ERROR can only call other `min_const_fn`
const fn bar() -> u32 { foo() } //~ ERROR can only call other `const`

#[unstable(feature = "rust1", issue="0")]
const fn foo2() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const fn bar2() -> u32 { foo2() } //~ ERROR can only call other `min_const_fn`
const fn bar2() -> u32 { foo2() } //~ ERROR can only call other `const`

#[stable(feature = "rust1", since = "1.0.0")]
// conformity is required, even with `const_fn` feature gate
Expand All @@ -31,6 +31,6 @@ const fn foo2_gated() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const fn bar2_gated() -> u32 { foo2_gated() } //~ ERROR can only call other `min_const_fn`
const fn bar2_gated() -> u32 { foo2_gated() } //~ ERROR can only call other `const`

fn main() {}
6 changes: 3 additions & 3 deletions src/test/ui/consts/min_const_fn/min_const_fn_libstd_stability.stderr
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Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_fn_libstd_stability.rs:15:25
|
LL | const fn bar() -> u32 { foo() }
| ^^^^^
|
= help: add #![feature(const_fn)] to the crate attributes to enable

error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_fn_libstd_stability.rs:22:26
|
LL | const fn bar2() -> u32 { foo2() }
Expand All @@ -22,7 +22,7 @@ LL | const fn bar3() -> u32 { (5f32 + 6f32) as u32 }
|
= help: add #![feature(const_fn)] to the crate attributes to enable

error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_fn_libstd_stability.rs:34:32
|
LL | const fn bar2_gated() -> u32 { foo2_gated() }
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4 changes: 2 additions & 2 deletions src/test/ui/consts/min_const_fn/min_const_unsafe_fn_libstd_stability.rs
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Expand Up @@ -12,14 +12,14 @@ const unsafe fn foo() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const unsafe fn bar() -> u32 { unsafe { foo() } } //~ ERROR can only call other `min_const_fn`
const unsafe fn bar() -> u32 { unsafe { foo() } } //~ ERROR can only call other `const`

#[unstable(feature = "rust1", issue="0")]
const unsafe fn foo2() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const unsafe fn bar2() -> u32 { unsafe { foo2() } } //~ ERROR can only call other `min_const_fn`
const unsafe fn bar2() -> u32 { unsafe { foo2() } } //~ ERROR can only call other `const`

#[stable(feature = "rust1", since = "1.0.0")]
// conformity is required, even with `const_fn` feature gate
Expand Down
6 changes: 3 additions & 3 deletions src/test/ui/consts/min_const_fn/min_const_unsafe_fn_libstd_stability.stderr
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Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_unsafe_fn_libstd_stability.rs:15:41
|
LL | const unsafe fn bar() -> u32 { unsafe { foo() } }
| ^^^^^
|
= help: add #![feature(const_fn)] to the crate attributes to enable

error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_unsafe_fn_libstd_stability.rs:22:42
|
LL | const unsafe fn bar2() -> u32 { unsafe { foo2() } }
Expand All @@ -22,7 +22,7 @@ LL | const unsafe fn bar3() -> u32 { (5f32 + 6f32) as u32 }
|
= help: add #![feature(const_fn)] to the crate attributes to enable

error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_unsafe_fn_libstd_stability.rs:34:48
|
LL | const unsafe fn bar2_gated() -> u32 { unsafe { foo2_gated() } }
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6 changes: 3 additions & 3 deletions src/test/ui/consts/min_const_fn/min_const_unsafe_fn_libstd_stability2.rs
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Expand Up @@ -12,21 +12,21 @@ const fn foo() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const unsafe fn bar() -> u32 { foo() } //~ ERROR can only call other `min_const_fn`
const unsafe fn bar() -> u32 { foo() } //~ ERROR can only call other `const`

#[unstable(feature = "rust1", issue="0")]
const fn foo2() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const unsafe fn bar2() -> u32 { foo2() } //~ ERROR can only call other `min_const_fn`
const unsafe fn bar2() -> u32 { foo2() } //~ ERROR can only call other `const`

// check whether this function cannot be called even with the feature gate active
#[unstable(feature = "foo2", issue="0")]
const fn foo2_gated() -> u32 { 42 }

#[stable(feature = "rust1", since = "1.0.0")]
// can't call non-min_const_fn
const unsafe fn bar2_gated() -> u32 { foo2_gated() } //~ ERROR can only call other `min_const_fn`
const unsafe fn bar2_gated() -> u32 { foo2_gated() } //~ ERROR can only call other `const`

fn main() {}
6 changes: 3 additions & 3 deletions src/test/ui/consts/min_const_fn/min_const_unsafe_fn_libstd_stability2.stderr
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Original file line number Diff line number Diff line change
@@ -1,20 +1,20 @@
error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_unsafe_fn_libstd_stability2.rs:15:32
|
LL | const unsafe fn bar() -> u32 { foo() }
| ^^^^^
|
= help: add #![feature(const_fn)] to the crate attributes to enable

error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_unsafe_fn_libstd_stability2.rs:22:33
|
LL | const unsafe fn bar2() -> u32 { foo2() }
| ^^^^^^
|
= help: add #![feature(const_fn)] to the crate attributes to enable

error[E0723]: can only call other `min_const_fn` within a `min_const_fn` (see issue #57563)
error[E0723]: can only call other `const` within a `const` (see issue #57563)
--> $DIR/min_const_unsafe_fn_libstd_stability2.rs:30:39
|
LL | const unsafe fn bar2_gated() -> u32 { foo2_gated() }
Expand Down