Check reference expression operator

[turbolent]

Closes #1406

Description

Reference expressions and casting expressions have the same syntax, so reference expressions are parsed by parsing casting expressions.

Ensure the casting expression has the correct operator (as).

At least make the current syntax / parsing strict, but we still might want to change the syntax has discussed.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #1566 (7bc31c1) into master (423ef34) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1566   +/-   ##
=======================================
  Coverage   74.73%   74.73%           
=======================================
  Files         289      289           
  Lines       55659    55673   +14     
=======================================
+ Hits        41595    41607   +12     
- Misses      12563    12565    +2     
  Partials     1501     1501           

Flag	Coverage Δ
unittests	74.73% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/ast/expression.go	87.61% <ø> (ø)
runtime/parser2/expression.go	92.88% <100.00%> (+0.07%)	⬆️
runtime/sema/simple_type.go	92.30% <0.00%> (-3.85%)	⬇️
runtime/sema/check_member_expression.go	97.64% <0.00%> (+0.01%)	⬆️

---

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[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit 07c27c2
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Results

	old.txt	new.txt
	time/op		delta
ContractInterfaceFungibleToken-2	48.8µs ± 1%	49.9µs ± 3%	+2.30%	(p=0.008 n=6+7)
RuntimeFungibleTokenTransfer-2	1.52ms ±32%	1.68ms ±24%	~	(p=0.456 n=7+7)
RuntimeResourceDictionaryValues-2	16.7ms ± 6%	17.0ms ± 4%	~	(p=0.456 n=7+7)
ParseFungibleToken-2	230µs ± 3%	237µs ± 4%	~	(p=0.132 n=6+6)
ParseArray-2	15.8ms ±13%	15.4ms ± 4%	~	(p=0.620 n=7+7)
ParseInfix-2	10.0µs ± 3%	10.1µs ± 2%	~	(p=0.388 n=7+6)
ParseDeploy/byte_array-2	24.6ms ±15%	24.3ms ± 8%	~	(p=1.000 n=7+7)
ParseDeploy/decode_hex-2	1.43ms ± 4%	1.43ms ± 2%	~	(p=1.000 n=7+7)
QualifiedIdentifierCreation/One_level-2	3.34ns ± 3%	3.30ns ± 7%	~	(p=0.259 n=7+7)
QualifiedIdentifierCreation/Three_levels-2	168ns ± 4%	170ns ± 4%	~	(p=0.318 n=7+7)
CheckContractInterfaceFungibleTokenConformance-2	172µs ± 2%	176µs ± 3%	~	(p=0.101 n=6+7)
NewInterpreter/new_interpreter-2	1.41µs ± 5%	1.37µs ± 1%	~	(p=0.054 n=7+6)
NewInterpreter/new_sub-interpreter-2	2.67µs ± 7%	2.69µs ± 4%	~	(p=0.535 n=7+7)
InterpretRecursionFib-2	3.19ms ± 3%	3.19ms ± 3%	~	(p=1.000 n=7+7)
	alloc/op		delta
RuntimeFungibleTokenTransfer-2	273kB ± 0%	273kB ± 0%	~	(p=1.000 n=7+7)
RuntimeResourceDictionaryValues-2	4.05MB ± 0%	4.05MB ± 0%	~	(p=0.383 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	66.2kB ± 0%	66.2kB ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	26.6kB ± 0%	26.6kB ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	848B ± 0%	848B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.34kB ± 0%	1.34kB ± 0%	~	(all equal)
InterpretRecursionFib-2	1.26MB ± 0%	1.26MB ± 0%	~	(p=0.639 n=7+7)
	allocs/op		delta
RuntimeFungibleTokenTransfer-2	4.54k ± 0%	4.54k ± 0%	~	(p=0.423 n=7+7)
RuntimeResourceDictionaryValues-2	102k ± 0%	102k ± 0%	~	(p=0.764 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00	0.00	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	2.00 ± 0%	2.00 ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	458 ± 0%	458 ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	13.0 ± 0%	13.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	40.0 ± 0%	40.0 ± 0%	~	(all equal)
InterpretRecursionFib-2	26.2k ± 0%	26.2k ± 0%	~	(all equal)

[dsainati1]

I agree that this is an improvement over not doing the check, but I think this error is going to be very confusing to people. If people were using as! and as? instead of as because they didn't understand the difference between a reference and a cast, complaining that they are using the wrong one is not going to make sense. IMO at least until we have time to address the syntax similarity we should include something in the text of the error that either explains the difference or at least links to the docs.

[SupunS]

This sounds like a good temporary solution to me

[turbolent]

@dsainati1 Agreed. We won't merge this for Secure Cadence, I just opened it so we would at least start to do something about it, even if just reporting some error until we have a proper decision about what to do here (e.g change the syntax, like discussed before).

[...] we should include something in the text of the error that either explains the difference or at least links to the docs.
Could you maybe add this? You might be better at phrasing this than I would

[turbolent]

Replaced by #1661