Rollup merge of rust-lang#142271 - workingjubilee:fn-ptrs-have-two-different-lints, r=RalfJung

compiler: fn ptrs should hit different lints based on ABI

I was looking closer at the code for linting on ABIs and realized a mistake was probably made during rebase or review. I think that for function pointers in the HIR, the lint that fires should probably depend on the ABI we encountered, e.g. if it's on the newly-deprecated set of ABIs or not. This will be slightly confusing for a little bit, but I think we can do more to reduce that confusion by switching `unsupported_fn_ptr_calling_conventions` to a hard error.

r? `@RalfJung`

Author: fmease

compiler/rustc_hir_analysis/src/check/check.rs

@@ -37,22 +37,23 @@ use {rustc_attr_data_structures as attrs, rustc_hir as hir};
 use super::compare_impl_item::check_type_bounds;
 use super::*;
 
+fn add_abi_diag_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}`"
+        ));
+    }
+}
+
 pub fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: ExternAbi) {
     // FIXME: this should be checked earlier, e.g. in `rustc_ast_lowering`, to fix
     // things like #86232.
-    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 AbiMap::from_target(&tcx.sess.target).canonize_abi(abi, false) {
         AbiMapping::Direct(..) => (),
@@ -63,13 +64,13 @@ pub fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: ExternAbi
                 E0570,
                 "`{abi}` is not a supported ABI for the current target",
             );
-            add_help(abi, &mut err);
+            add_abi_diag_help(abi, &mut err);
             err.emit();
         }
         AbiMapping::Deprecated(..) => {
             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);
+                add_abi_diag_help(abi, lint);
             });
         }
     }
@@ -80,7 +81,16 @@ pub fn check_abi_fn_ptr(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: Ex
     // in `check_abi` above.
     match AbiMap::from_target(&tcx.sess.target).canonize_abi(abi, false) {
         AbiMapping::Direct(..) => (),
-        AbiMapping::Deprecated(..) | AbiMapping::Invalid => {
+        // This is not a redundant match arm: these ABIs started linting after introducing
+        // UNSUPPORTED_FN_PTR_CALLING_CONVENTIONS already existed and we want to
+        // avoid expanding the scope of that lint so it can move to a hard error sooner.
+        AbiMapping::Deprecated(..) => {
+            tcx.node_span_lint(UNSUPPORTED_CALLING_CONVENTIONS, hir_id, span, |lint| {
+                lint.primary_message("use of calling convention not supported on this target");
+                add_abi_diag_help(abi, lint);
+            });
+        }
+        AbiMapping::Invalid => {
             tcx.node_span_lint(UNSUPPORTED_FN_PTR_CALLING_CONVENTIONS, hir_id, span, |lint| {
                 lint.primary_message(format!(
                     "the calling convention {abi} is not supported on this target"

tests/ui/abi/unsupported.aarch64.stderr

@@ -114,43 +114,44 @@ LL | fn stdcall_ptr(f: extern "stdcall" fn()) {
    = note: for more information, see issue #130260 <https://github.com/rust-lang/rust/issues/130260>
 
 error[E0570]: `"stdcall"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:117:1
+  --> $DIR/unsupported.rs:119:1
    |
 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
+  --> $DIR/unsupported.rs:123:1
    |
 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:129:17
+warning: use of calling convention not supported on this target
+  --> $DIR/unsupported.rs:131:17
    |
 LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    |                 ^^^^^^^^^^^^^^^^^^^
    |
    = 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 #130260 <https://github.com/rust-lang/rust/issues/130260>
+   = 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:134:1
+  --> $DIR/unsupported.rs:136:1
    |
 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
+  --> $DIR/unsupported.rs:139:1
    |
 LL | extern "cdecl-unwind" {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -160,7 +161,7 @@ LL | extern "cdecl-unwind" {}
    = help: use `extern "C-unwind"` instead
 
 warning: the calling convention "vectorcall" is not supported on this target
-  --> $DIR/unsupported.rs:143:22
+  --> $DIR/unsupported.rs:145:22
    |
 LL | fn vectorcall_ptr(f: extern "vectorcall" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -169,13 +170,13 @@ 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:148:1
+  --> $DIR/unsupported.rs:150:1
    |
 LL | extern "vectorcall" {}
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: the calling convention "C-cmse-nonsecure-call" is not supported on this target
-  --> $DIR/unsupported.rs:151:21
+  --> $DIR/unsupported.rs:153:21
    |
 LL | fn cmse_call_ptr(f: extern "C-cmse-nonsecure-call" fn()) {
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -184,7 +185,7 @@ 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:159:22
+  --> $DIR/unsupported.rs:161:22
    |
 LL | fn cmse_entry_ptr(f: extern "C-cmse-nonsecure-entry" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -193,7 +194,7 @@ 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:164:1
+  --> $DIR/unsupported.rs:166:1
    |
 LL | extern "C-cmse-nonsecure-entry" {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -255,7 +256,7 @@ 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:126:1
+  --> $DIR/unsupported.rs:128:1
    |
 LL | extern "cdecl" fn cdecl() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -265,13 +266,13 @@ LL | extern "cdecl" fn cdecl() {}
    = help: use `extern "C"` instead
 
 error[E0570]: `"vectorcall"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:141:1
+  --> $DIR/unsupported.rs:143:1
    |
 LL | extern "vectorcall" fn vectorcall() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0570]: `"C-cmse-nonsecure-entry"` is not a supported ABI for the current target
-  --> $DIR/unsupported.rs:157:1
+  --> $DIR/unsupported.rs:159:1
    |
 LL | extern "C-cmse-nonsecure-entry" fn cmse_entry() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -368,19 +369,20 @@ LL | fn stdcall_ptr(f: extern "stdcall" fn()) {
    = note: `#[warn(unsupported_fn_ptr_calling_conventions)]` on by default
 
 Future breakage diagnostic:
-warning: the calling convention "cdecl" is not supported on this target
-  --> $DIR/unsupported.rs:129:17
+warning: use of calling convention not supported on this target
+  --> $DIR/unsupported.rs:131:17
    |
 LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    |                 ^^^^^^^^^^^^^^^^^^^
    |
    = 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 #130260 <https://github.com/rust-lang/rust/issues/130260>
-   = note: `#[warn(unsupported_fn_ptr_calling_conventions)]` on by default
+   = 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:134:1
+  --> $DIR/unsupported.rs:136:1
    |
 LL | extern "cdecl" {}
    | ^^^^^^^^^^^^^^^^^
@@ -392,7 +394,7 @@ LL | extern "cdecl" {}
 
 Future breakage diagnostic:
 warning: use of calling convention not supported on this target
-  --> $DIR/unsupported.rs:137:1
+  --> $DIR/unsupported.rs:139:1
    |
 LL | extern "cdecl-unwind" {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -404,7 +406,7 @@ LL | extern "cdecl-unwind" {}
 
 Future breakage diagnostic:
 warning: the calling convention "vectorcall" is not supported on this target
-  --> $DIR/unsupported.rs:143:22
+  --> $DIR/unsupported.rs:145:22
    |
 LL | fn vectorcall_ptr(f: extern "vectorcall" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -415,7 +417,7 @@ 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:151:21
+  --> $DIR/unsupported.rs:153:21
    |
 LL | fn cmse_call_ptr(f: extern "C-cmse-nonsecure-call" fn()) {
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -426,7 +428,7 @@ 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:159:22
+  --> $DIR/unsupported.rs:161:22
    |
 LL | fn cmse_entry_ptr(f: extern "C-cmse-nonsecure-entry" fn()) {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -437,7 +439,7 @@ 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:126:1
+  --> $DIR/unsupported.rs:128:1
    |
 LL | extern "cdecl" fn cdecl() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^