PR Checklist

• Addresses an existing open issue:fixesBug: [no-unnecessary-condition] Improper checking of optional chaining of defined method return value #7912
• That issue was marked asaccepting prs
• Steps inContributing were taken

Overview

This pr improves unnecessary optional chaining checking ofno-unnecessary-condition.
In below example, optional chain iny()?. is unnecessary becausey does not return nullable value.
As described in#7912, the currentno-unnecessary-condition does not check for the following case.

typeT1={y:()=>number}|null;declareconstx1:T1;x1?.y()?.toExponential();

I addedisCallExpressionNullableOriginFromCallee function.
This function takes a CallExpression node as an argument. It returnstrue if the call expression's nullable type is origin from callee otherwise returnsfalse.

// isCallExpressionNullableOriginFromCallee will return true for given call expression `y()`typeT1={y:()=>number}|null;declareconstx1:T1;x1?.y()?.toExponential();//    ^^^ y()'s nullable type is origin from T1's nullable type// isCallExpressionNullableOriginFromCallee will return false for given call expression `y()`typeT1={y:()=>number|null}|null;declareconstx1:T1;x1?.y()?.toExponential();//    ^^^ y()'s nullable type is origin from it's own definition. (() => number | null)