Suggest to specify a target triple when lang item is missing #91820

rukai · 2021-12-12T03:04:48Z

It is very common for newbies to embedded to hit this confusing error when forgetting to specify the target.
Source: me googling this error many times.

Possible changes

We could possibly restrict the note+help to only be included on eh_personality lang item if that helped reduce false positives, but its also possible doing so would just increase false negatives
Open to any suggestions on rewriting the messages
We could possibly remove the .cargo/config alternative to avoid the message getting too noisy but I think its valuable to have as its the correct approach for most embedded projects so that cargo build just works.

r? rust-lang/diagnostics

davidtwco

I think this is a sensible change, I've left some suggestions for the wording/style but otherwise looks good.

davidtwco · 2021-12-13T09:49:41Z

compiler/rustc_passes/src/weak_lang_items.rs

+                    .sess
+                    .diagnostic()
+                    .struct_err(&format!("language item required, but not found: `{}`", name))
+                    .note(&format!("This occurs when a binary crate with `#![no_std]` is compiled for a target that usually gets `{}` from the standard library.", name))


Suggested change

.note(&format!("This occurs when a binary crate with `#![no_std]` is compiled for a target that usually gets `{}` from the standard library.", name))

.note(&format!("this can occur when a binary crate with `#![no_std]` is compiled for a target where `{}` is defined in the standard library.", name))

nit: wording change + lowercase diagnostic message

davidtwco · 2021-12-13T09:53:19Z

compiler/rustc_passes/src/weak_lang_items.rs

+                    .struct_err(&format!("language item required, but not found: `{}`", name))
+                    .note(&format!("This occurs when a binary crate with `#![no_std]` is compiled for a target that usually gets `{}` from the standard library.", name))
+                    .help(&format!(
+r#"If you want to compile for a specific target_triple that doesnt need `{}`, then make sure to run with `--target target_triple` or add the following to the crate's `.cargo/config` file:


Suggested change

r#"If you want to compile for a specific target_triple that doesnt need `{}`, then make sure to run with `--target target_triple` or add the following to the crate's `.cargo/config` file:

"you may be able to compile for a target that doesn't need `{}`, specify a target with `--target` or in `.cargo/config`"

nit: wording

I don't know if there are other diagnostics where we reference what to do in Cargo, might be worth checking if there is precedent.

I searched for other references to .cargo/config and didnt find any.
But I did stumble across this earlier:

rust/compiler/rustc_metadata/src/locator.rs

Lines 1151 to 1156 in 2ca9333

// NOTE: this suggests using rustup, even though the user may not have it installed.

// That's because they could choose to install it; or this may give them a hint which

// target they need to install from their distro.

if missing_core {

err.help(&format!(

"consider downloading the target with `rustup target add {}`",

Which references what to do in rustup.
It also makes the case that its useful even when the user doesnt have rustup because it gives a hint what you would have to do in the equivalent tool.
In this case it hints that you should probably set the target in your build system of choice.

davidtwco · 2021-12-13T09:54:12Z

compiler/rustc_passes/src/weak_lang_items.rs

@@ -70,7 +70,19 @@ fn verify<'tcx>(tcx: TyCtxt<'tcx>, items: &lang_items::LanguageItems) {
                    tcx.sess.note_without_error("Use `#![feature(default_alloc_error_handler)]` for a default error handler");


Suggested change

tcx.sess.note_without_error("Use `#![feature(default_alloc_error_handler)]` for a default error handler");

tcx.sess.note_without_error("use `#![feature(default_alloc_error_handler)]` for a default error handler");

pre-existing: our diagnostics are typically always lowercase, could you add a commit changing this?

…issing

rukai · 2021-12-13T13:12:45Z

The suggested changes are a big improvement, thanks!

davidtwco · 2021-12-13T18:04:03Z

@bors r+

bors · 2021-12-13T18:04:04Z

📌 Commit fae40c5 has been approved by davidtwco

… r=davidtwco Suggest to specify a target triple when lang item is missing It is very common for newbies to embedded to hit this confusing error when forgetting to specify the target. Source: me googling this error many times. ## Possible changes * We could possibly restrict the note+help to only be included on eh_personality lang item if that helped reduce false positives, but its also possible doing so would just increase false negatives * Open to any suggestions on rewriting the messages * We could possibly remove the `.cargo/config` alternative to avoid the message getting too noisy but I think its valuable to have as its the correct approach for most embedded projects so that `cargo build` just works. r? rust-lang/diagnostics

…askrgr Rollup of 7 pull requests Successful merges: - rust-lang#91529 (add BinaryHeap::try_reserve and BinaryHeap::try_reserve_exact) - rust-lang#91820 (Suggest to specify a target triple when lang item is missing) - rust-lang#91851 (Make `MaybeUninit::zeroed` `const`) - rust-lang#91875 (Use try_normalize_erasing_regions in RevealAllVisitor) - rust-lang#91887 (Remove `in_band_lifetimes` from `rustc_const_eval`) - rust-lang#91892 (Fix HashStable implementation on InferTy) - rust-lang#91893 (Remove `in_band_lifetimes` from `rustc_hir`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

rust-highfive assigned davidtwco Dec 12, 2021

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 12, 2021

camelid added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Dec 13, 2021

davidtwco requested changes Dec 13, 2021

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davidtwco 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 Dec 13, 2021

Suggest to specify a target triple when eh_personality lang item is m…

fae40c5

…issing

rukai force-pushed the help_with_personality_issues branch from 018d5ae to fae40c5 Compare December 13, 2021 13:04

davidtwco approved these changes Dec 13, 2021

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 13, 2021

matthiaskrgr mentioned this pull request Dec 14, 2021

Rollup of 8 pull requests #91897

Closed

matthiaskrgr mentioned this pull request Dec 14, 2021

Rollup of 7 pull requests #91902

Merged

bors merged commit dfec47f into rust-lang:master Dec 14, 2021

rustbot added this to the 1.59.0 milestone Dec 14, 2021

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Suggest to specify a target triple when lang item is missing #91820

Suggest to specify a target triple when lang item is missing #91820

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rukai commented Dec 12, 2021

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bors commented Dec 13, 2021

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	.note(&format!("This occurs when a binary crate with `#![no_std]` is compiled for a target that usually gets `{}` from the standard library.", name))
	.note(&format!("this can occur when a binary crate with `#![no_std]` is compiled for a target where `{}` is defined in the standard library.", name))

	r#"If you want to compile for a specific target_triple that doesnt need `{}`, then make sure to run with `--target target_triple` or add the following to the crate's `.cargo/config` file:
	"you may be able to compile for a target that doesn't need `{}`, specify a target with `--target` or in `.cargo/config`"

	// NOTE: this suggests using rustup, even though the user may not have it installed.
	// That's because they could choose to install it; or this may give them a hint which
	// target they need to install from their distro.
	if missing_core {
	err.help(&format!(
	"consider downloading the target with `rustup target add {}`",

		@@ -70,7 +70,19 @@ fn verify<'tcx>(tcx: TyCtxt<'tcx>, items: &lang_items::LanguageItems) {
		tcx.sess.note_without_error("Use `#![feature(default_alloc_error_handler)]` for a default error handler");

Suggest to specify a target triple when lang item is missing #91820

Suggest to specify a target triple when lang item is missing #91820

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rukai commented Dec 12, 2021

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