Fix completion preselection in ternary conditional expressions

[Copilot]

Completions within ternary conditionals inside function arguments weren't preselecting the expected type. For example:

function bar(z: string, x: Foo) { return x; }
const a = '';

bar(a, a == '' ? ); // Foo not preselected after ?
bar(a, a == '' ? : ); // Foo not preselected after :

Changes

• Added getContextualTypeForConditionalExpression helper to get contextual type from parent conditional expression
• Handle KindQuestionToken and KindColonToken cases when parent is ConditionalExpression
• Fallthrough to default case for KindColonToken when not in conditional (preserves object literal, type annotation behavior)

The fix uses the parent ConditionalExpression node to locate the containing call expression, enabling proper contextual type inference.

Original prompt

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This section details on the original issue you should resolve

<issue_title>No "recommended" completion entry when outer context is incomplete ternary conditional operator</issue_title>
<issue_description>From microsoft/TypeScript#59517

For the code:

export enum Bar { }
export enum Foo { }


function foo(x: Foo) { return x; }
function bar(z: string, x: Foo) { return x; }

const a = '';

// Trigger suggestions here
foo(); // Selects `Foo` first
bar(a, a == '' ? ); // doesn't select `Foo` first

1. Trigger suggestions after the incomplete ternary

Expected
Foo is selected first

Actual
I see Bar selected first. It works correctly in the Foo function

cc @bpasero</issue_description>

<agent_instructions>To test this, create a fourslash test which does completions with markers within the foo call, and after the ? in the bar call. Something like:

export enum Bar { }
export enum Foo { }


function foo(x: Foo) { return x; }
function bar(z: string, x: Foo) { return x; }

const a = '';

foo(/*1*/);
bar(a, a == '' ? /*2*/);

Use print debugging with go test -v to figure out a fix.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes No "recommended" completion entry when outer context is incomplete ternary conditional operator #2196

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[Copilot]

Pull request overview

This PR fixes completion preselection when the cursor is positioned within a ternary conditional expression inside function arguments. Previously, completions after ? or : in ternary conditionals weren't preselecting the expected type.

Key Changes

• Added contextual type handling for ternary conditionals by implementing getContextualTypeForConditionalExpression helper
• Enhanced getContextualType switch statement to handle KindQuestionToken and KindColonToken when parent is a conditional expression
• Added comprehensive test coverage for all ternary completion scenarios

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/ls/completions.go	Implements contextual type resolution for completions in ternary conditional expressions by adding a new helper function and handling question/colon tokens
internal/fourslash/tests/manual/completionInTernaryConditional_test.go	Adds comprehensive test coverage for completion preselection in ternary conditionals, including incomplete ternaries and both branches