Fix Claude no-arg tool calling in streaming mode (#229)

* Don't error when Claude does a no-arg tool call in streaming mode
* Make tool calling unit test use streaming

R/provider-claude.R

@@ -166,7 +166,10 @@ method(stream_merge_chunks, ProviderClaude) <- function(provider, result, chunk)
     if (chunk$delta$type == "text_delta") {
       paste(result$content[[chunk$index + 1L]]$text) <- chunk$delta$text
     } else if (chunk$delta$type == "input_json_delta") {
-      paste(result$content[[chunk$index + 1L]]$input) <- chunk$delta$partial_json
+      if (chunk$delta$partial_json != "") {
+        # See issue #228 about partial_json sometimes being ""
+        paste(result$content[[chunk$index + 1L]]$input) <- chunk$delta$partial_json
+      }
     } else {
       cli::cli_inform(c("!" = "Unknown delta type {.str {chunk$delta$type}}."))
     }

tests/testthat/helper-provider.R

@@ -52,7 +52,7 @@ test_tools_simple <- function(chat_fun) {
   chat <- chat_fun(system_prompt = "Be very terse, not even punctuation.")
   chat$register_tool(tool(function() "2024-01-01", "Return the current date"))
 
-  result <- chat$chat("What's the current date in YMD format?")
+  result <- chat$chat("What's the current date in YMD format?", echo = TRUE)
   expect_match(result, "2024-01-01")
 
   result <- chat$chat("What month is it? Provide the full name")