Proposal: add BSL (1C Enterprise) language support

Summary

BSL is the programming language of 1C:Enterprise and OneScript — a business-app platform used heavily across the post-Soviet region and Europe. This proposal wraps https://github.com/1c-syntax/bsl-language-server (403⭐, MIT, Java 17) as a new Language adapter in multilspy.

Motivation

• BSL codebases routinely exceed 2 000 modules; ERP configurations reach 10 000+.
• No LSP-based BSL tooling exists in the Python ecosystem today.
• We are building an LLM-driven refactoring orchestrator on top of multilspy, currently via a private fork using internal APIs.
• Upstream adoption lets downstream tools depend on multilspy>=X.Y instead of maintaining forks.
• Opens BSL to multilspy's existing semantic-tooling ecosystem (Serena et al.).

Evidence (from our internal integration, 2026-04)

Scope

Minimal additive change, matching the eclipse_jdtls / kotlin_language_server pattern.

• `Language.BSL = "bsl"` added to multilspy_config.py.
• Factory branch added to language_server.py.
• New package language_servers/bsl_language_server/ with 4 files:
  • bsl_language_server.py — subclasses LanguageServer, launches java -jar bsl-language-server.jar --lsp as an argv list.
  • runtime_dependencies.json — pins BSL LS 0.22.0 with verified SHA256, downloads from GitHub releases on first use.
  • initialize_params.json — BSL-specific capabilities.
  • __init__.py.
• Three integration tests in tests/multilspy/test_multilspy_bsl.py, skipped when java is not on PATH.
• .gitignore entry for bsl_language_server/static/ (matches other JAR-based adapters).

No changes to core / protocol / other adapters. Python-only, no C extensions, no new runtime deps.

Non-goals

• `workspace/didChangeWorkspaceFolders` eager indexing — tracked separately upstream at 1c-syntax/bsl-language-server. Current adapter uses per-document didOpen, same as Java / Kotlin.
• Diagnostics / code actions — `window/logMessage` and `publishDiagnostics` acknowledged but not surfaced.

Prerequisites

• Java 17+ on PATH (BSL LS is a Spring Boot app built for JDK 17).
• First run downloads ~94 MB JAR; subsequent runs read from static/<version>/.

Next step

If the proposal is acceptable in principle, I have a ready branch on my fork (Alex1980Alex/multilspy:feat/bsl-language, 2 commits, +387/−2 lines) and will open a PR linked to this issue. Happy to iterate on scope before the PR is opened.

Start by comparing the existing eclipse_jdtls and kotlin_language_server adapters in multilspy_config.py and language_server.py. Then review the proposed language_servers/bsl_language_server/ files, runtime_dependencies.json, and tests/multilspy/test_multilspy_bsl.py; completion means the BSL adapter, pinned download, ignore rule, and Java-gated integration tests match the stated scope.