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Rollup merge of #88782 - asquared31415:issue-79559, r=cjgillot

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Fix ICE when `start` lang item has wrong generics

In my previous pr #87875 I missed the requirements on the `start` lang item due to its relative difficulty to test and opting for more conservative estimates.  This fixes that by updating the requirement to be exactly one generic type.

The `start` lang item should have exactly one generic type for the return type of the `main` fn ptr passed to it.  I believe having zero would previously *sometimes* compile (often with the use of `fn() -> ()` as the fn ptr but it was likely UB to call if the return type of `main` was not `()` as far as I know) however it also sometimes would not for various errors including ICEs and LLVM errors depending on exact situations.  Having more than 1 generic has always failed with an ICE because only the one generic type is expected and provided.

Fixes #79559, fixes #73584, fixes #83117 (all duplicates)
Relevant to #9307

r? ````@cjgillot````
This commit is contained in:
Manish Goregaokar 2021-09-30 18:05:20 -07:00 • committed by GitHub
commit 3d86aac990
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6 changed files with 35 additions and 15 deletions
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compiler/rustc_hir/src/lang_items.rs
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@ -300,7 +300,7 @@ language_item_table! {
Oom, sym::oom, oom, Target::Fn, GenericRequirement::None;
AllocLayout, sym::alloc_layout, alloc_layout, Target::Struct, GenericRequirement::None;
Start, sym::start, start_fn, Target::Fn, GenericRequirement::None;
Start, sym::start, start_fn, Target::Fn, GenericRequirement::Exact(1);
EhPersonality, sym::eh_personality, eh_personality, Target::Fn, GenericRequirement::None;
EhCatchTypeinfo, sym::eh_catch_typeinfo, eh_catch_typeinfo, Target::Static, GenericRequirement::None;