Correctly implement citation merging for gemini

Fixes #358

Author: hadley

NEWS.md

@@ -1,5 +1,8 @@
 # ellmer (development version)
 
+* `chat_gemini()` can now handle responses that include citation metadata 
+  (#358).
+
 * `live_browser()` now initializes `shinychat::chat_ui()` with the messages from
   the chat turns, rather than replaying the turns server-side (#381).
 

R/provider-gemini.R

@@ -325,6 +325,10 @@ merge_optional <- function(merge_func) {
   function(left, right, path = NULL) {
     if (is.null(left) && is.null(right)) {
       NULL
+    } else if (is.null(left)) {
+      right
+    } else if (is.null(right)) {
+      left
     } else {
       merge_func(left, right, path)
     }
@@ -405,6 +409,7 @@ merge_parts <- function() {
 }
 
 # Put it all together...
+# https://ai.google.dev/api/generate-content#v1beta.GenerateContentResponse
 merge_gemini_chunks <- merge_objects(
   candidates = merge_candidate_lists(
     content = merge_objects(

tests/testthat/test-provider-gemini.R

@@ -76,3 +76,32 @@ test_that("can merge text output", {
   ))
   expect_equal(out$candidates[[1]]$finishReason, "STOP")
 })
+
+test_that("can handle citations", {
+  # based on "Write me a 5-paragraph essay on the history of the tidyverse."
+  messages <- c(
+    '{"candidates": [{"content": {"parts": [{"text": "a"}]}, "role": "model"}]}',
+    '{"candidates": [{
+      "content": {"parts": [{"text": "a"}]},
+      "role": "model",
+      "citationMetadata": {
+        "citationSources": [
+          {
+            "startIndex": 1,
+            "endIndex": 2,
+            "uri": "https://example.com",
+            "license": ""
+          }
+        ]
+      }
+    }]}'
+  )
+  chunks <- lapply(messages, jsonlite::parse_json)
+
+  out <- merge_gemini_chunks(chunks[[1]], chunks[[2]])
+  source <- out$candidates[[1]]$citationMetadata$citationSources[[1]]
+  expect_equal(source$startIndex, 1)
+  expect_equal(source$endIndex, 2)
+  expect_equal(source$uri, "https://example.com")
+  expect_equal(source$license, "")
+})