remove support for the #[start] attribute

Author: RalfJung

Diff for: compiler/rustc_ast/src/entry.rs

@@ -19,12 +19,6 @@ pub enum EntryPointType {
     /// fn main() {}
     /// ```
     RustcMainAttr,
-    /// This is a function with the `#[start]` attribute.
-    /// ```ignore (clashes with test entrypoint)
-    /// #[start]
-    /// fn main() {}
-    /// ```
-    Start,
     /// This function is **not** an entrypoint but simply named `main` (not at the root).
     /// This is only used for diagnostics.
     /// ```
@@ -41,9 +35,7 @@ pub fn entry_point_type(
     at_root: bool,
     name: Option<Symbol>,
 ) -> EntryPointType {
-    if attr::contains_name(attrs, sym::start) {
-        EntryPointType::Start
-    } else if attr::contains_name(attrs, sym::rustc_main) {
+    if attr::contains_name(attrs, sym::rustc_main) {
         EntryPointType::RustcMainAttr
     } else if let Some(name) = name
         && name == sym::main

Diff for: compiler/rustc_ast_passes/src/feature_gate.rs

@@ -231,18 +231,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemKind::Fn(..) => {
-                if attr::contains_name(&i.attrs, sym::start) {
-                    gate!(
-                        &self,
-                        start,
-                        i.span,
-                        "`#[start]` functions are experimental and their signature may change \
-                         over time"
-                    );
-                }
-            }
-
             ast::ItemKind::Struct(..) => {
                 for attr in attr::filter_by_name(&i.attrs, sym::repr) {
                     for item in attr.meta_item_list().unwrap_or_else(ThinVec::new) {

Diff for: compiler/rustc_builtin_macros/src/test_harness.rs

@@ -205,11 +205,11 @@ impl<'a> MutVisitor for EntryPointCleaner<'a> {
         ast::mut_visit::walk_item(self, item);
         self.depth -= 1;
 
-        // Remove any #[rustc_main] or #[start] from the AST so it doesn't
+        // Remove any #[rustc_main] from the AST so it doesn't
         // clash with the one we're going to add, but mark it as
         // #[allow(dead_code)] to avoid printing warnings.
         match entry_point_type(&item, self.depth == 0) {
-            EntryPointType::MainNamed | EntryPointType::RustcMainAttr | EntryPointType::Start => {
+            EntryPointType::MainNamed | EntryPointType::RustcMainAttr => {
                 let allow_dead_code = attr::mk_attr_nested_word(
                     &self.sess.psess.attr_id_generator,
                     ast::AttrStyle::Outer,
@@ -218,8 +218,7 @@ impl<'a> MutVisitor for EntryPointCleaner<'a> {
                     sym::dead_code,
                     self.def_site,
                 );
-                item.attrs
-                    .retain(|attr| !attr.has_name(sym::rustc_main) && !attr.has_name(sym::start));
+                item.attrs.retain(|attr| !attr.has_name(sym::rustc_main));
                 item.attrs.push(allow_dead_code);
             }
             EntryPointType::None | EntryPointType::OtherMain => {}

Diff for: compiler/rustc_codegen_cranelift/src/main_shim.rs

@@ -1,7 +1,7 @@
 use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use rustc_hir::LangItem;
 use rustc_middle::ty::{AssocKind, GenericArg};
-use rustc_session::config::{EntryFnType, sigpipe};
+use rustc_session::config::EntryFnType;
 use rustc_span::DUMMY_SP;
 use rustc_span::symbol::Ident;
 
@@ -15,10 +15,9 @@ pub(crate) fn maybe_create_entry_wrapper(
     is_jit: bool,
     is_primary_cgu: bool,
 ) {
-    let (main_def_id, (is_main_fn, sigpipe)) = match tcx.entry_fn(()) {
+    let (main_def_id, sigpipe) = match tcx.entry_fn(()) {
         Some((def_id, entry_ty)) => (def_id, match entry_ty {
-            EntryFnType::Main { sigpipe } => (true, sigpipe),
-            EntryFnType::Start => (false, sigpipe::DEFAULT),
+            EntryFnType::Main { sigpipe } => sigpipe,
         }),
         None => return,
     };
@@ -32,14 +31,13 @@ pub(crate) fn maybe_create_entry_wrapper(
         return;
     }
 
-    create_entry_fn(tcx, module, main_def_id, is_jit, is_main_fn, sigpipe);
+    create_entry_fn(tcx, module, main_def_id, is_jit, sigpipe);
 
     fn create_entry_fn(
         tcx: TyCtxt<'_>,
         m: &mut dyn Module,
         rust_main_def_id: DefId,
         ignore_lang_start_wrapper: bool,
-        is_main_fn: bool,
         sigpipe: u8,
     ) {
         let main_ret_ty = tcx.fn_sig(rust_main_def_id).no_bound_vars().unwrap().output();
@@ -95,8 +93,8 @@ pub(crate) fn maybe_create_entry_wrapper(
 
             let main_func_ref = m.declare_func_in_func(main_func_id, &mut bcx.func);
 
-            let result = if is_main_fn && ignore_lang_start_wrapper {
-                // regular main fn, but ignoring #[lang = "start"] as we are running in the jit
+            let result = if ignore_lang_start_wrapper {
+                // ignoring #[lang = "start"] as we are running in the jit
                 // FIXME set program arguments somehow
                 let call_inst = bcx.ins().call(main_func_ref, &[]);
                 let call_results = bcx.func.dfg.inst_results(call_inst).to_owned();
@@ -134,7 +132,8 @@ pub(crate) fn maybe_create_entry_wrapper(
                     types::I64 => bcx.ins().sextend(types::I64, res),
                     _ => unimplemented!("16bit systems are not yet supported"),
                 }
-            } else if is_main_fn {
+            } else {
+                // Regular main fn invoked via start lang item.
                 let start_def_id = tcx.require_lang_item(LangItem::Start, None);
                 let start_instance = Instance::expect_resolve(
                     tcx,
@@ -151,10 +150,6 @@ pub(crate) fn maybe_create_entry_wrapper(
                 let call_inst =
                     bcx.ins().call(func_ref, &[main_val, arg_argc, arg_argv, arg_sigpipe]);
                 bcx.inst_results(call_inst)[0]
-            } else {
-                // using user-defined start fn
-                let call_inst = bcx.ins().call(main_func_ref, &[arg_argc, arg_argv]);
-                bcx.inst_results(call_inst)[0]
             };
 
             bcx.ins().return_(&[result]);

Diff for: compiler/rustc_codegen_ssa/src/base.rs

@@ -490,8 +490,8 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         let ptr_ty = cx.type_ptr();
         let (arg_argc, arg_argv) = get_argc_argv(&mut bx);
 
-        let (start_fn, start_ty, args, instance) = if let EntryFnType::Main { sigpipe } = entry_type
-        {
+        let EntryFnType::Main { sigpipe } = entry_type;
+        let (start_fn, start_ty, args, instance) = {
             let start_def_id = cx.tcx().require_lang_item(LangItem::Start, None);
             let start_instance = ty::Instance::expect_resolve(
                 cx.tcx(),
@@ -512,10 +512,6 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 vec![rust_main, arg_argc, arg_argv, arg_sigpipe],
                 Some(start_instance),
             )
-        } else {
-            debug!("using user-defined start fn");
-            let start_ty = cx.type_func(&[isize_ty, ptr_ty], isize_ty);
-            (rust_main, start_ty, vec![arg_argc, arg_argv], None)
         };
 
         let result = bx.call(start_ty, None, None, start_fn, &args, None, instance);
@@ -530,7 +526,8 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     }
 }
 
-/// Obtain the `argc` and `argv` values to pass to the rust start function.
+/// Obtain the `argc` and `argv` values to pass to the rust start function
+/// (i.e., the "start" lang item).
 fn get_argc_argv<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(bx: &mut Bx) -> (Bx::Value, Bx::Value) {
     if bx.cx().sess().target.os.contains("uefi") {
         // Params for UEFI

Diff for: compiler/rustc_error_codes/src/error_codes/E0132.md

@@ -1,3 +1,5 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A function with the `start` attribute was declared with type parameters.
 
 Erroneous code example:

Diff for: compiler/rustc_error_codes/src/error_codes/E0138.md

@@ -1,3 +1,5 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 More than one function was declared with the `#[start]` attribute.
 
 Erroneous code example:

Diff for: compiler/rustc_error_codes/src/error_codes/E0647.md

@@ -1,3 +1,5 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `start` function was defined with a where clause.
 
 Erroneous code example:

Diff for: compiler/rustc_feature/src/builtin_attrs.rs

@@ -447,7 +447,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Entry point:
-    ungated!(start, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::No),
 

Diff for: compiler/rustc_feature/src/removed.rs

@@ -223,8 +223,9 @@ declare_features! (
     (removed, rustc_diagnostic_macros, "1.38.0", None, None),
     /// Allows identifying crates that contain sanitizer runtimes.
     (removed, sanitizer_runtime, "1.17.0", None, None),
-    (removed, simd, "1.0.0", Some(27731),
-     Some("removed in favor of `#[repr(simd)]`")),
+    (removed, simd, "1.0.0", Some(27731), Some("removed in favor of `#[repr(simd)]`")),
+    /// Allows using `#[start]` on a function indicating that it is the program entrypoint.
+    (removed, start, "1.0.0", Some(29633), Some("not portable enough and never RFC'd")),
     /// Allows `#[link(kind = "static-nobundle", ...)]`.
     (removed, static_nobundle, "1.16.0", Some(37403),
      Some(r#"subsumed by `#[link(kind = "static", modifiers = "-bundle", ...)]`"#)),

Diff for: compiler/rustc_feature/src/unstable.rs

@@ -299,8 +299,6 @@ declare_features! (
     (internal, rustdoc_internals, "1.58.0", Some(90418)),
     /// Allows using the `rustdoc::missing_doc_code_examples` lint
     (unstable, rustdoc_missing_doc_code_examples, "1.31.0", Some(101730)),
-    /// Allows using `#[start]` on a function indicating that it is the program entrypoint.
-    (unstable, start, "1.0.0", Some(29633)),
     /// Allows using `#[structural_match]` which indicates that a type is structurally matchable.
     /// FIXME: Subsumed by trait `StructuralPartialEq`, cannot move to removed until a library
     /// feature with the same name exists.

Diff for: compiler/rustc_hir_analysis/messages.ftl

@@ -477,21 +477,6 @@ hir_analysis_simd_ffi_highly_experimental = use of SIMD type{$snip} in FFI is hi
 hir_analysis_specialization_trait = implementing `rustc_specialization_trait` traits is unstable
     .help = add `#![feature(min_specialization)]` to the crate attributes to enable
 
-hir_analysis_start_function_parameters = `#[start]` function is not allowed to have type parameters
-    .label = `#[start]` function cannot have type parameters
-
-hir_analysis_start_function_where = `#[start]` function is not allowed to have a `where` clause
-    .label = `#[start]` function cannot have a `where` clause
-
-hir_analysis_start_not_async = `#[start]` function is not allowed to be `async`
-    .label = `#[start]` is not allowed to be `async`
-
-hir_analysis_start_not_target_feature = `#[start]` function is not allowed to have `#[target_feature]`
-    .label = `#[start]` function is not allowed to have `#[target_feature]`
-
-hir_analysis_start_not_track_caller = `#[start]` function is not allowed to be `#[track_caller]`
-    .label = `#[start]` function is not allowed to be `#[track_caller]`
-
 hir_analysis_static_specialize = cannot specialize on `'static` lifetime
 
 hir_analysis_tait_forward_compat = item constrains opaque type that is not in its signature

Diff for: compiler/rustc_hir_analysis/src/check/entry.rs

@@ -5,7 +5,7 @@ use rustc_hir as hir;
 use rustc_hir::Node;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::span_bug;
-use rustc_middle::ty::{self, Ty, TyCtxt, TypingMode};
+use rustc_middle::ty::{self, TyCtxt, TypingMode};
 use rustc_session::config::EntryFnType;
 use rustc_span::Span;
 use rustc_span::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
@@ -19,7 +19,6 @@ use crate::errors;
 pub(crate) fn check_for_entry_fn(tcx: TyCtxt<'_>) {
     match tcx.entry_fn(()) {
         Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
-        Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
         _ => {}
     }
 }
@@ -193,83 +192,3 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         });
     }
 }
-
-fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
-    let start_def_id = start_def_id.expect_local();
-    let start_id = tcx.local_def_id_to_hir_id(start_def_id);
-    let start_span = tcx.def_span(start_def_id);
-    let start_t = tcx.type_of(start_def_id).instantiate_identity();
-    match start_t.kind() {
-        ty::FnDef(..) => {
-            if let Node::Item(it) = tcx.hir_node(start_id) {
-                if let hir::ItemKind::Fn(sig, generics, _) = &it.kind {
-                    let mut error = false;
-                    if !generics.params.is_empty() {
-                        tcx.dcx().emit_err(errors::StartFunctionParameters { span: generics.span });
-                        error = true;
-                    }
-                    if generics.has_where_clause_predicates {
-                        tcx.dcx().emit_err(errors::StartFunctionWhere {
-                            span: generics.where_clause_span,
-                        });
-                        error = true;
-                    }
-                    if sig.header.asyncness.is_async() {
-                        let span = tcx.def_span(it.owner_id);
-                        tcx.dcx().emit_err(errors::StartAsync { span });
-                        error = true;
-                    }
-
-                    let attrs = tcx.hir().attrs(start_id);
-                    for attr in attrs {
-                        if attr.has_name(sym::track_caller) {
-                            tcx.dcx().emit_err(errors::StartTrackCaller {
-                                span: attr.span,
-                                start: start_span,
-                            });
-                            error = true;
-                        }
-                        if attr.has_name(sym::target_feature)
-                            // Calling functions with `#[target_feature]` is
-                            // not unsafe on WASM, see #84988
-                            && !tcx.sess.target.is_like_wasm
-                            && !tcx.sess.opts.actually_rustdoc
-                        {
-                            tcx.dcx().emit_err(errors::StartTargetFeature {
-                                span: attr.span,
-                                start: start_span,
-                            });
-                            error = true;
-                        }
-                    }
-
-                    if error {
-                        return;
-                    }
-                }
-            }
-
-            let expected_sig = ty::Binder::dummy(tcx.mk_fn_sig(
-                [tcx.types.isize, Ty::new_imm_ptr(tcx, Ty::new_imm_ptr(tcx, tcx.types.u8))],
-                tcx.types.isize,
-                false,
-                hir::Safety::Safe,
-                ExternAbi::Rust,
-            ));
-
-            let _ = check_function_signature(
-                tcx,
-                ObligationCause::new(
-                    start_span,
-                    start_def_id,
-                    ObligationCauseCode::StartFunctionType,
-                ),
-                start_def_id.into(),
-                expected_sig,
-            );
-        }
-        _ => {
-            span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
-        }
-    }
-}

Diff for: compiler/rustc_hir_analysis/src/errors.rs

@@ -620,48 +620,6 @@ pub(crate) struct TargetFeatureOnMain {
     pub main: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(hir_analysis_start_not_track_caller)]
-pub(crate) struct StartTrackCaller {
-    #[primary_span]
-    pub span: Span,
-    #[label]
-    pub start: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(hir_analysis_start_not_target_feature)]
-pub(crate) struct StartTargetFeature {
-    #[primary_span]
-    pub span: Span,
-    #[label]
-    pub start: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(hir_analysis_start_not_async, code = E0752)]
-pub(crate) struct StartAsync {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(hir_analysis_start_function_where, code = E0647)]
-pub(crate) struct StartFunctionWhere {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(hir_analysis_start_function_parameters, code = E0132)]
-pub(crate) struct StartFunctionParameters {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(hir_analysis_main_function_return_type_generic, code = E0131)]
 pub(crate) struct MainFunctionReturnTypeGeneric {

Diff for: compiler/rustc_passes/messages.ftl

@@ -496,11 +496,6 @@ passes_multiple_rustc_main =
     .first = first `#[rustc_main]` function
     .additional = additional `#[rustc_main]` function
 
-passes_multiple_start_functions =
-    multiple `start` functions
-    .label = multiple `start` functions
-    .previous = previous `#[start]` function here
-
 passes_must_not_suspend =
     `must_not_suspend` attribute should be applied to a struct, enum, union, or trait
     .label = is not a struct, enum, union, or trait