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 +37,33 @@ 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 suffix = if unwind { "-unwind" } else { "" };
+            diag.help(format!("use `extern \"C{suffix}\"` instead",));
+        } else if let ExternAbi::Stdcall { unwind } = abi {
+            let suffix = if unwind { "-unwind" } else { "" };
+            diag.help(format!(
+                "if you need `extern \"stdcall{suffix}\"` on win32 and `extern \"C{suffix}\"` everywhere else, use `extern \"system{suffix}\"`"
+            ));
+        }
+    }
     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

@@ -118,6 +118,8 @@ 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"`
 
 warning: the calling convention "cdecl" is not supported on this target
   --> $DIR/unsupported.rs:125:17
@@ -136,6 +138,7 @@ 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: the calling convention "vectorcall" is not supported on this target
@@ -230,6 +233,8 @@ 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
@@ -239,6 +244,7 @@ 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
@@ -363,6 +369,7 @@ 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:
@@ -407,5 +414,6 @@ 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
 

tests/ui/abi/unsupported.arm.stderr

@@ -103,6 +103,8 @@ 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"`
 
 warning: the calling convention "cdecl" is not supported on this target
   --> $DIR/unsupported.rs:125:17
@@ -121,6 +123,7 @@ 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: the calling convention "vectorcall" is not supported on this target
@@ -209,6 +212,8 @@ 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
@@ -218,6 +223,7 @@ 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
@@ -331,6 +337,7 @@ 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:
@@ -375,5 +382,6 @@ 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
 

tests/ui/abi/unsupported.riscv32.stderr

@@ -103,6 +103,8 @@ 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"`
 
 warning: the calling convention "cdecl" is not supported on this target
   --> $DIR/unsupported.rs:125:17
@@ -121,6 +123,7 @@ 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: the calling convention "vectorcall" is not supported on this target
@@ -209,6 +212,8 @@ 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
@@ -218,6 +223,7 @@ 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
@@ -331,6 +337,7 @@ 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:
@@ -375,5 +382,6 @@ 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
 

tests/ui/abi/unsupported.riscv64.stderr

@@ -103,6 +103,8 @@ 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"`
 
 warning: the calling convention "cdecl" is not supported on this target
   --> $DIR/unsupported.rs:125:17
@@ -121,6 +123,7 @@ 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: the calling convention "vectorcall" is not supported on this target
@@ -209,6 +212,8 @@ 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
@@ -218,6 +223,7 @@ 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
@@ -331,6 +337,7 @@ 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:
@@ -375,5 +382,6 @@ 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
 

tests/ui/abi/unsupported.x64.stderr

@@ -103,6 +103,8 @@ 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"`
 
 warning: the calling convention "cdecl" is not supported on this target
   --> $DIR/unsupported.rs:125:17
@@ -121,6 +123,7 @@ 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: the calling convention "C-cmse-nonsecure-call" is not supported on this target
@@ -194,6 +197,8 @@ 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
@@ -203,6 +208,7 @@ 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]: `"C-cmse-nonsecure-entry"` is not a supported ABI for the current target
   --> $DIR/unsupported.rs:150:1
@@ -310,6 +316,7 @@ 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:
@@ -343,5 +350,6 @@ 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
 

tests/ui/abi/unsupported.x64_win.stderr

@@ -106,6 +106,7 @@ LL | extern "stdcall" {}
    |
    = 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: if you need `extern "stdcall"` on win32 and `extern "C"` everywhere else, use `extern "system"`
    = note: `#[warn(unsupported_calling_conventions)]` on by default
 
 warning: the calling convention "cdecl" is not supported on this target
@@ -125,6 +126,7 @@ 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
 
 warning: the calling convention "C-cmse-nonsecure-call" is not supported on this target
   --> $DIR/unsupported.rs:144:21
@@ -158,6 +160,7 @@ 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
 
 error[E0570]: `"ptx-kernel"` is not a supported ABI for the current target
   --> $DIR/unsupported.rs:36:1
@@ -209,6 +212,7 @@ LL | extern "stdcall" fn stdcall() {}
    |
    = 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: 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
@@ -218,6 +222,7 @@ 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]: `"C-cmse-nonsecure-entry"` is not a supported ABI for the current target
   --> $DIR/unsupported.rs:150:1
@@ -314,6 +319,7 @@ LL | extern "stdcall" {}
    |
    = 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: if you need `extern "stdcall"` on win32 and `extern "C"` everywhere else, use `extern "system"`
    = note: `#[warn(unsupported_calling_conventions)]` on by default
 
 Future breakage diagnostic:
@@ -336,6 +342,7 @@ 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:
@@ -369,6 +376,7 @@ 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:
@@ -380,6 +388,7 @@ LL | extern "stdcall" fn stdcall() {}
    |
    = 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: if you need `extern "stdcall"` on win32 and `extern "C"` everywhere else, use `extern "system"`
    = note: `#[warn(unsupported_calling_conventions)]` on by default
 
 Future breakage diagnostic:
@@ -391,5 +400,6 @@ 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