Refactor Error Code definitions

This refactors the way error codes are handled, in preparation for
making JSONRPC.jl less LSP specific, by hooking into custom error printing
provided by an upstream PR.

src/LanguageServer.jl

@@ -17,6 +17,69 @@ using .URIs2
 
 JSON.lower(uri::URI) = string(uri)
 
+# these are the endpoints of JSON-RPC error codes
+# per the LSP spec, no LSP error codes should lie
+# between these
+const SERVER_ERROR_END       = -32000
+const SERVER_ERROR_START     = -32099
+
+# These are existing reserved errors for JSONRPC.jl
+# We shouldn't throw these manually
+const SERVER_NOT_INITIALIZED = -32002
+const UNKNOWN_ERROR_CODE     = -32001
+
+# LSP specific error codes
+# these are the defined ranges for LSP errors
+# not real error codes. Custom errors must lie
+# outside this range
+const LSP_RESERVED_ERROR_START = -32899
+const LSP_RESERVED_ERROR_END   = -32800
+
+const REQUEST_CANCELLED      = -32800
+const CONTENT_MODIFIED       = -32801
+const SERVER_CANCELLED       = -32802
+const REQUEST_FAILED         = -32803
+
+# Specific to our implementation
+const NO_DOCUMENT        = -33100
+const MISMATCHED_VERSION = -33101
+const SHUTDOWN_REQUEST   = -32600
+
+const ERROR_CODES = (
+    REQUEST_CANCELLED,
+    CONTENT_MODIFIED,
+    SERVER_CANCELLED,
+    REQUEST_FAILED,
+    NO_DOCUMENT,
+    MISMATCHED_VERSION,
+    SHUTDOWN_REQUEST
+)
+
+function __init__()
+    # init JSONRPC error messages
+    conflicting_codes = filter(ERROR_CODES) do code
+        !haskey(JSONRPC.JSONRPCErrorStrings, code) && return false
+        return JSONRPC.JSONRPCErrorStrings[code] != "ServerError"
+    end
+    # if any of the codes we want to use are already set,
+    # it means we have a conflict with another application
+    # using JSONRPC.jl at the same time in this process
+    # warn the user of this, so that they can debug/work around it
+    if !isempty(conflicting_codes)
+        @warn """JSONRPC Error Codes conflict!
+
+        Another library besides LanguageServer.jl is using JSONRPC.jl with conflicting error codes.
+        LanguageServer.jl will overwrite this with its own state. Faulty behavior/error printing may arise.
+        """ Codes=conflicting_codes
+    end
+
+    JSONRPC.RPCErrorStrings[REQUEST_CANCELLED]      = "RequestCancelled"
+    JSONRPC.RPCErrorStrings[CONTENT_MODIFIED]       = "ContentModified"
+    JSONRPC.RPCErrorStrings[SERVER_CANCELLED]       = "ServerCancelled"
+    JSONRPC.RPCErrorStrings[REQUEST_FAILED]         = "RequestFailed"
+    nothing
+end
+
 include("exception_types.jl")
 include("protocol/protocol.jl")
 include("extensions/extensions.jl")

src/languageserverinstance.jl

@@ -257,7 +257,7 @@ function request_wrapper(func, server::LanguageServerInstance)
             # it's fine to always return a value here, even for notifications, because
             # JSONRPC discards it anyways in that case
             return JSONRPC.JSONRPCError(
-                -32600,
+                SHUTDOWN_REQUEST,
                 "LS shutdown was requested.",
                 nothing
             )

src/utilities.jl

@@ -3,15 +3,15 @@
 
 function nodocument_error(uri, data=nothing)
     return JSONRPC.JSONRPCError(
-        -33100,
+        NO_DOCUMENT,
         "document $(uri) requested but not present in the JLS",
         data
     )
 end
 
 function mismatched_version_error(uri, doc, params, msg, data=nothing)
     return JSONRPC.JSONRPCError(
-        -33101,
+        MISMATCHED_VERSION,
         "version mismatch in $(msg) request for $(uri): JLS $(get_version(doc)), client: $(params.version)",
         data
     )