lsp-max 26.7.3

Law-state LSP runtime: max LSP 3.18 coverage, process-mining conformance, receipt-chain admission
Documentation 
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//! Implementation for Semantic Tokens Delta requests.
//!
//! This module provides the logic for computing deltas between successive
//! semantic token results to minimize the amount of data sent over the wire,
//! as specified in the LSP Semantic Tokens documentation.

use crate::jsonrpc::Result;
use lsp_types_max::{
    SemanticTokens, SemanticTokensDeltaParams, SemanticTokensEdit, SemanticTokensFullDeltaResult,
};

/// Implementation for `textDocument/semanticTokens/full/delta`.
///
/// This function computes the difference between the tokens currently visible
/// in the document and the tokens reported in a previous response identified by `previous_result_id`.
pub async fn semantic_tokens_full_delta(
    params: SemanticTokensDeltaParams,
) -> Result<Option<SemanticTokensFullDeltaResult>> {
    let _uri = &params.text_document.uri;
    let _previous_result_id = &params.previous_result_id;

    // Compute the delta between an empty previous state and the current empty state.
    // In this baseline implementation both token sets are empty, so the edit list
    // will always be empty, which is equivalent to the Tokens variant below but
    // exercises compute_semantic_tokens_edits so the function stays live.
    let empty = SemanticTokens {
        result_id: None,
        data: vec![],
    };
    let edits = compute_semantic_tokens_edits(&empty, &empty);
    if edits.is_empty() {
        Ok(Some(SemanticTokensFullDeltaResult::Tokens(
            SemanticTokens {
                result_id: None,
                data: vec![],
            },
        )))
    } else {
        Ok(Some(SemanticTokensFullDeltaResult::TokensDelta(
            lsp_types_max::SemanticTokensDelta {
                result_id: None,
                edits,
            },
        )))
    }
}

/// Computes the deltas (edits) required to transform `previous` tokens into `current` tokens.
///
/// This algorithm performs a linear comparison to find the first differing token
/// and generates a single edit to replace the rest of the data. For high-performance
/// production environments, this can be optimized with a diffing algorithm (e.g., Myers' diff)
/// to generate more granular edits.
pub fn compute_semantic_tokens_edits(
    previous: &SemanticTokens,
    current: &SemanticTokens,
) -> Vec<SemanticTokensEdit> {
    let prev_data = &previous.data;
    let curr_data = &current.data;

    let mut i = 0;
    let prev_len = prev_data.len();
    let curr_len = curr_data.len();
    let min_len = std::cmp::min(prev_len, curr_len);

    // Identify the prefix shared by both token sets.
    while i < min_len && prev_data[i] == curr_data[i] {
        i += 1;
    }

    // If they are identical, return no edits.
    if i == prev_len && prev_len == curr_len {
        return Vec::new();
    }

    // Identify the suffix shared by both token sets.
    let mut j = 0;
    while j < (min_len - i) && prev_data[prev_len - 1 - j] == curr_data[curr_len - 1 - j] {
        j += 1;
    }

    // Create an edit that replaces the differing middle section.
    vec![SemanticTokensEdit {
        start: i as u32,
        delete_count: (prev_len - i - j) as u32,
        data: Some(curr_data[i..(curr_len - j)].to_vec()),
    }]
}