Fix C/C++ debug hover on intermediate members of a dereferenced expression

[tieo]

Problem

On a line that begins an expression with */& (e.g. if (*a.b.c == X) where a.b is a
struct), hovering an intermediate member (a or b) while debugging shows no value.
Without the leading operator it works fine; Watch/Variables are unaffected.

Cause

No EvaluatableExpressionProvider is registered for C/C++, so VS Code's default is used. It keeps
the leading * and clips on the right, so hovering b sends *a.b to the debug adapter — a
dereference of the non-pointer member a.b — which errors.

Fix

Register an EvaluatableExpressionProvider that, only for an intermediate member of a
*/&-prefixed chain, returns the expression without the leading operator (a.b). Every other
case returns undefined, so the default behavior (./->/::, and legitimate *ptr derefs on
the final segment) is unchanged.

Note: I created the code in this PR using the LLM Opus 4.8, as well as the text above which was proofread by it.
I tested it manually in VS Code.

[tieo]

@microsoft-github-policy-service agree

[sean-mcmanus]

...see my other comments.

[Copilot]

Pull request overview

Registers a C/C++ EvaluatableExpressionProvider so debug hover evaluates the correct sub-expression when the hovered identifier is an intermediate member inside a */&-prefixed access chain (e.g. avoiding *a.b when hovering b in *a.b.c).

Changes:

• Added EvaluatableExpressionProvider implementation that conditionally strips leading */& for intermediate member hovers.
• Registered the provider during language server client initialization for the C/C++ document selector.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Extension/src/LanguageServer/Providers/evaluatableExpressionProvider.ts	Adds a custom evaluatable-expression computation to override VS Code’s default behavior in a narrow case.
Extension/src/LanguageServer/client.ts	Registers the new evaluatable expression provider for C/C++ documents.

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[tieo]

Addressed the review feedback in the latest commit:

• Moved the provider to Extension/src/Debugger/ and register it during debugger activation in Debugger/extension.ts instead of the language client.

On the Copilot suggestion to gate with line.charAt(clipEnd) === '.': I went a different way. The problem with that gate is it leaves *ptr->member doing what the default does, but that's already broken — -> has higher precedence than the unary *, so the expression is really *(ptr->member), and when you hover ptr you want to see ptr, not *ptr.

What it does now is keep the leading */& only when you're hovering the last segment of the chain, and drop it everywhere in the middle. That ends up being right whether the chain uses ., ->, or []. I also had to keep subscripts in the token because the default detection stops at the [, which is why hovering something like the c in a.b[i].c gave you nothing before. Function calls never get pulled in, so there's no risk of evaluating something with side effects.