add specific help messages for stdcall and cdecl

Author: RalfJung

compiler/rustc_hir_analysis/src/check/check.rs

@@ -4,8 +4,8 @@ use std::ops::ControlFlow;
 use rustc_abi::FieldIdx;
 use rustc_attr_data_structures::ReprAttr::ReprPacked;
 use rustc_data_structures::unord::{UnordMap, UnordSet};
-use rustc_errors::MultiSpan;
 use rustc_errors::codes::*;
+use rustc_errors::{EmissionGuarantee, MultiSpan};
 use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::{LangItem, Node, intravisit};
 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
@@ -37,20 +37,35 @@ use super::compare_impl_item::check_type_bounds;
 use super::*;
 
 pub fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: ExternAbi) {
+    fn add_help<T: EmissionGuarantee>(abi: ExternAbi, diag: &mut Diag<'_, T>) {
+        if let ExternAbi::Cdecl { unwind } = abi {
+            let c_abi = ExternAbi::C { unwind };
+            diag.help(format!("use `extern {c_abi}` instead",));
+        } else if let ExternAbi::Stdcall { unwind } = abi {
+            let c_abi = ExternAbi::C { unwind };
+            let system_abi = ExternAbi::System { unwind };
+            diag.help(format!(
+                "if you need `extern {abi}` on win32 and `extern {c_abi}` everywhere else, \
+                use `extern {system_abi}`"
+            ));
+        }
+    }
     match tcx.sess.target.is_abi_supported(abi) {
         Some(true) => (),
         Some(false) => {
-            struct_span_code_err!(
+            let mut err = struct_span_code_err!(
                 tcx.dcx(),
                 span,
                 E0570,
                 "`{abi}` is not a supported ABI for the current target",
-            )
-            .emit();
+            );
+            add_help(abi, &mut err);
+            err.emit();
         }
         None => {
             tcx.node_span_lint(UNSUPPORTED_CALLING_CONVENTIONS, hir_id, span, |lint| {
                 lint.primary_message("use of calling convention not supported on this target");
+                add_help(abi, lint);
             });
         }
     }

tests/ui/abi/unsupported.aarch64.stderr

@@ -118,9 +118,19 @@ error[E0570]: `"stdcall"` is not a supported ABI for the current target
    |
 LL | extern "stdcall" {}
    | ^^^^^^^^^^^^^^^^^^^
+   |
+   = help: if you need `extern "stdcall"` on win32 and `extern "C"` everywhere else, use `extern "system"`
+
+error[E0570]: `"stdcall-unwind"` is not a supported ABI for the current target
+  --> $DIR/unsupported.rs:121:1
+   |
+LL | extern "stdcall-unwind" {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: if you need `extern "stdcall-unwind"` on win32 and `extern "C-unwind"` everywhere else, use `extern "system-unwind"`
 
 warning: the calling convention "cdecl" is not supported on this target
-  --> $DIR/unsupported.rs:125:17
+  --> $DIR/unsupported.rs:129:17
    |
 LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    |                 ^^^^^^^^^^^^^^^^^^^
@@ -129,17 +139,28 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    = note: for more information, see issue #130260 <https://github.com/rust-lang/rust/issues/130260>
 
 warning: use of calling convention not supported on this target
-  --> $DIR/unsupported.rs:130:1
+  --> $DIR/unsupported.rs:134:1
    |
 LL | extern "cdecl" {}
    | ^^^^^^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
+   = help: use `extern "C"` instead
    = note: `#[warn(unsupported_calling_conventions)]` on by default
 
+warning: use of calling convention not supported on this target
+  --> $DIR/unsupported.rs:137:1
+   |
+LL | extern "cdecl-unwind" {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
+   = help: use `extern "C-unwind"` instead
+
 warning: the calling convention "vectorcall" is not supported on this target
-  --> $DIR/unsupported.rs:136:22
+  --> $DIR/unsupported.rs:143:22
    |
 LL | fn vectorcall_ptr(f: extern "vectorcall" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -148,13 +169,13 @@ LL | fn vectorcall_ptr(f: extern "vectorcall" fn()) {
    = note: for more information, see issue #130260 <https://github.com/rust-lang/rust/issues/130260>
 
 error[E0570]: `"vectorcall"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:141:1
+  --> $DIR/unsupported.rs:148:1
    |
 LL | extern "vectorcall" {}
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: the calling convention "C-cmse-nonsecure-call" is not supported on this target
-  --> $DIR/unsupported.rs:144:21
+  --> $DIR/unsupported.rs:151:21
    |
 LL | fn cmse_call_ptr(f: extern "C-cmse-nonsecure-call" fn()) {
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -163,7 +184,7 @@ LL | fn cmse_call_ptr(f: extern "C-cmse-nonsecure-call" fn()) {
    = note: for more information, see issue #130260 <https://github.com/rust-lang/rust/issues/130260>
 
 warning: the calling convention "C-cmse-nonsecure-entry" is not supported on this target
-  --> $DIR/unsupported.rs:152:22
+  --> $DIR/unsupported.rs:159:22
    |
 LL | fn cmse_entry_ptr(f: extern "C-cmse-nonsecure-entry" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -172,7 +193,7 @@ LL | fn cmse_entry_ptr(f: extern "C-cmse-nonsecure-entry" fn()) {
    = note: for more information, see issue #130260 <https://github.com/rust-lang/rust/issues/130260>
 
 error[E0570]: `"C-cmse-nonsecure-entry"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:157:1
+  --> $DIR/unsupported.rs:164:1
    |
 LL | extern "C-cmse-nonsecure-entry" {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -230,29 +251,32 @@ error[E0570]: `"stdcall"` is not a supported ABI for the current target
    |
 LL | extern "stdcall" fn stdcall() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: if you need `extern "stdcall"` on win32 and `extern "C"` everywhere else, use `extern "system"`
 
 warning: use of calling convention not supported on this target
-  --> $DIR/unsupported.rs:122:1
+  --> $DIR/unsupported.rs:126:1
    |
 LL | extern "cdecl" fn cdecl() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
+   = help: use `extern "C"` instead
 
 error[E0570]: `"vectorcall"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:134:1
+  --> $DIR/unsupported.rs:141:1
    |
 LL | extern "vectorcall" fn vectorcall() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0570]: `"C-cmse-nonsecure-entry"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:150:1
+  --> $DIR/unsupported.rs:157:1
    |
 LL | extern "C-cmse-nonsecure-entry" fn cmse_entry() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 21 previous errors; 14 warnings emitted
+error: aborting due to 22 previous errors; 15 warnings emitted
 
 For more information about this error, try `rustc --explain E0570`.
 Future incompatibility report: Future breakage diagnostic:
@@ -345,7 +369,7 @@ LL | fn stdcall_ptr(f: extern "stdcall" fn()) {
 
 Future breakage diagnostic:
 warning: the calling convention "cdecl" is not supported on this target
-  --> $DIR/unsupported.rs:125:17
+  --> $DIR/unsupported.rs:129:17
    |
 LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    |                 ^^^^^^^^^^^^^^^^^^^
@@ -356,18 +380,31 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
 
 Future breakage diagnostic:
 warning: use of calling convention not supported on this target
-  --> $DIR/unsupported.rs:130:1
+  --> $DIR/unsupported.rs:134:1
    |
 LL | extern "cdecl" {}
    | ^^^^^^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
+   = help: use `extern "C"` instead
+   = note: `#[warn(unsupported_calling_conventions)]` on by default
+
+Future breakage diagnostic:
+warning: use of calling convention not supported on this target
+  --> $DIR/unsupported.rs:137:1
+   |
+LL | extern "cdecl-unwind" {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
+   = help: use `extern "C-unwind"` instead
    = note: `#[warn(unsupported_calling_conventions)]` on by default
 
 Future breakage diagnostic:
 warning: the calling convention "vectorcall" is not supported on this target
-  --> $DIR/unsupported.rs:136:22
+  --> $DIR/unsupported.rs:143:22
    |
 LL | fn vectorcall_ptr(f: extern "vectorcall" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -378,7 +415,7 @@ LL | fn vectorcall_ptr(f: extern "vectorcall" fn()) {
 
 Future breakage diagnostic:
 warning: the calling convention "C-cmse-nonsecure-call" is not supported on this target
-  --> $DIR/unsupported.rs:144:21
+  --> $DIR/unsupported.rs:151:21
    |
 LL | fn cmse_call_ptr(f: extern "C-cmse-nonsecure-call" fn()) {
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -389,7 +426,7 @@ LL | fn cmse_call_ptr(f: extern "C-cmse-nonsecure-call" fn()) {
 
 Future breakage diagnostic:
 warning: the calling convention "C-cmse-nonsecure-entry" is not supported on this target
-  --> $DIR/unsupported.rs:152:22
+  --> $DIR/unsupported.rs:159:22
    |
 LL | fn cmse_entry_ptr(f: extern "C-cmse-nonsecure-entry" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -400,12 +437,13 @@ LL | fn cmse_entry_ptr(f: extern "C-cmse-nonsecure-entry" fn()) {
 
 Future breakage diagnostic:
 warning: use of calling convention not supported on this target
-  --> $DIR/unsupported.rs:122:1
+  --> $DIR/unsupported.rs:126:1
    |
 LL | extern "cdecl" fn cdecl() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
+   = help: use `extern "C"` instead
    = note: `#[warn(unsupported_calling_conventions)]` on by default