remove support for the #[start] attribute

Author: RalfJung

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

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) {

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 => {}

compiler/rustc_codegen_cranelift/example/alloc_example.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]);

compiler/rustc_codegen_cranelift/example/mod_bench.rs

@@ -512,7 +512,6 @@ impl<'gcc, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         } else {
             // If the symbol already exists, it is an error: for example, the user wrote
             // #[no_mangle] extern "C" fn main(..) {..}
-            // instead of #[start]
             None
         }
     }

compiler/rustc_codegen_cranelift/src/main_shim.rs

@@ -3,11 +3,12 @@
 // Run-time:
 //   status: signal
 
-#![feature(auto_traits, lang_items, no_core, start, intrinsics, rustc_attrs)]
+#![feature(auto_traits, lang_items, no_core, intrinsics, rustc_attrs)]
 #![allow(internal_features)]
 
 #![no_std]
 #![no_core]
+#![no_main]
 
 /*
  * Core
@@ -49,7 +50,7 @@ fn test_fail() -> ! {
     unsafe { intrinsics::abort() };
 }
 
-#[start]
-fn main(mut argc: isize, _argv: *const *const u8) -> isize {
+#[no_mangle]
+extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
     test_fail();
 }