feat: support parsing map type: map(k,v)

[xxchan]

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What's changed and what's your intention?

part of #17743

• parser: support parsing map(k,v) type.
• expr/type: support map cast

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[xxchan]

• feat: support parsing map type: map(k,v) #17860 : 3 dependent PRs (#17864 , #17980 , #17986 ) 👈
• feat: add map type to scalar/array/expr #17690
• refactor(types): simplify ArrayImpl::from_protobuf #17763
• main

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[chenzl25]

LGTM! Nice work.

[BugenZhao]

Shall we rebase this PR?

[BugenZhao]

Though implemented ingeniously, does it mean that we need to construct (and allocate) the new context per row? 😕

[xxchan]

The real reason was that I didn't fully understand what list_cast is doing, so I just chose to invoke it directly instead of imitating. 🤡

risingwave/src/expr/impl/src/scalar/cast.rs

Lines 200 to 205 in 34e9829

	let cast = build_func(
	PbType::Cast,
	ctx.return_type.as_list().clone(),
	vec![InputRefExpression::new(ctx.arg_types[0].as_list().clone(), 0).boxed()],
	)
	.unwrap();

[xxchan]

Well, list_cast also clones datatypes and allocates vec every time..