Move Fn* traits malformedness protections to typeck

[compiler-errors]

I found it strange that we were doing a custom well-formedness check just for the Fn* traits' call_* fn items. My understanding from the git history is that this is just to avoid ICEs later on in typeck.

Well, that well-formedness check isn't even implemented correctly for FnOnce::call_once, or FnMut::call_mut for that matter. Instead, this PR just makes the typeck checks more robust, and leaves it up to the call-site to report errors when lang items are implemented in funny ways.

This coincidentally fixes another ICE where a the Add lang item is implemented with a add item that's a const instead of a method.

[rustbot]

r? @TaKO8Ki

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[TaKO8Ki]

@bors r+ rollup

[bors]

📌 Commit 2a700d4 has been approved by TaKO8Ki

It is now in the queue for this repository.

[compiler-errors]

@bors rollup- not convinced this needs to be rolled up always

[bors]

⌛ Testing commit 2a700d4 with merge a8db02805ba30bf2063281d42930c63b75622890...

[bors]

💔 Test failed - checks-actions

[compiler-errors]

@bors retry

[rust-log-analyzer]

The job dist-i686-mingw failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[2561/3021] Building CXX object utils/UnicodeData/CMakeFiles/UnicodeNameMappingGenerator.dir/UnicodeNameMappingGenerator.cpp.obj
[2562/3021] Linking CXX static library lib\libLLVMInstrumentation.a
[2563/3021] Linking CXX static library lib\libLLVMAggressiveInstCombine.a
[2564/3021] Linking CXX static library lib\libLLVMVectorize.a
FAILED: lib/libLLVMVectorize.a 
cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E rm -f lib\libLLVMVectorize.a && D:\a\rust\rust\mingw32\bin\ar.exe qc lib\libLLVMVectorize.a  lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/LoadStoreVectorizer.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/LoopVectorizationLegality.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/LoopVectorize.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/SLPVectorizer.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/Vectorize.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VectorCombine.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VPlan.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VPlanHCFGBuilder.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VPlanRecipes.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VPlanSLP.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VPlanTransforms.cpp.obj lib/Transforms/Vectorize/CMakeFiles/LLVMVectorize.dir/VPlanVerifier.cpp.obj && D:\a\rust\rust\mingw32\bin\ranlib.exe lib\libLLVMVectorize.a && cd ."
D:\a\rust\rust\mingw32\bin\ar.exe: could not create temporary file whilst writing archive: no more archived files
[2565/3021] Linking CXX static library lib\libLLVMObjCARCOpts.a
[2566/3021] Building CXX object utils/yaml-bench/CMakeFiles/yaml-bench.dir/YAMLBench.cpp.obj
[2567/3021] Linking CXX static library lib\libLLVMInstCombine.a
[2568/3021] Linking CXX executable bin\llvm-PerfectShuffle.exe
[2568/3021] Linking CXX executable bin\llvm-PerfectShuffle.exe
[2569/3021] Linking CXX executable bin\FileCheck.exe
[2570/3021] Building CXX object utils/not/CMakeFiles/not.dir/not.cpp.obj
[2571/3021] Building CXX object tools/lto/CMakeFiles/LTO.dir/lto.cpp.obj
ninja: build stopped: subcommand failed.
command did not execute successfully, got: exit code: 1


build script failed, must exit now', C:\Users\runneradmin\.cargo\registry\src\index.crates.io-1cd66030c949c28d\cmake-0.1.48\src\lib.rs:975:5
 finished in 230.533 seconds
Build completed unsuccessfully in 0:06:35

[bors]

⌛ Testing commit 2a700d4 with merge 3200982...

[bors]

☀️ Test successful - checks-actions
Approved by: TaKO8Ki
Pushing 3200982 to master...

[rust-timer]

Finished benchmarking commit (3200982): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.1%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-3.0%	[-3.0%, -3.0%]	1
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	-3.0%	[-3.0%, -3.0%]	1

Cycles

This benchmark run did not return any relevant results for this metric.