A for condition that tests an optional value is made a boolean

[ASDAlexander77]

for (let node = head; node; node = node.next) with node: Node | undefined failed module verification under every memory model:

error: 'ts.Condition' op operand #0 must be , but got '!ts.optional<!ts.class<@Node, !ts.class_storage<@Node>>>'
error: module verification error

mlirGen(ForStatement) passed the condition to ts.Condition unchanged. mlirGen(WhileStatement), mlirGen(DoStatement) and mlirGen(IfStatement) cast a non-boolean condition to boolean first. The for condition now goes through the same cast. node !== undefined already produced a boolean, which is why that form worked.

Test

00for_optional_class_condition.ts runs a for over an optional class (in main and in a function), over a nullable (| null) class and over an optional string, and runs the same tests with while and if. It is registered for compile and JIT and in TSLANG_CORPUS (rc and none). On main it fails to compile with the error above.

ctest -C Release: 3858/3858 passed. gtest unittests were not built in this build tree.

Not covered here

• The test leaves out an empty string: "" is truthy in every condition (if, while, !, ?:), filed as An empty string "" is truthy in if / while / ! / ?: conditions #509.
• -mm=own rejects this list traversal ("borrows a field and cannot be stored"), with or without this fix and with node !== undefined too, so the test is not registered under own.
• while narrows the tested variable in its body (checkSafeCast); for still does not. Nothing in this test needs it.

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