deepseek: Fix empty text segments causing issues (#52199)

Bennet Bo Fenner created 2 weeks ago

## Context

Deepseek seems to have started to return empty text deltas, which causes
issues cause their upstream API does not like empty text blocks to be
included in their request.

In practice this caused issues like `An assistant message with
'tool_calls' must be followed by tool messages responding to each
'tool_call_id'..., because the payload looked like this:

```
User {
    content: "Call the now tool a bunch of times",
},
Assistant {
    content: Some(
        "",
    ),
},
Tool {
    content: "The current datetime is 2026-03-23T13:21:24.084848+00:00.",
    tool_call_id: "call_00_iozCfHXJAPR13XwHiAwJ9OEw",
},
```

Now we filter out that empty text, which seems to fix the issue. This
matches our implementation for OpenAI

Closes #51854

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## Self-Review Checklist

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Release Notes:

- deepseek: Fixed issue with tool calling (`An assistant message with
'tool_calls' must be followed by tool messages responding to each
'tool_call_id'...`)

Change summary

crates/language_models/src/provider/deepseek.rs | 32 +++++++++++++-----
1 file changed, 22 insertions(+), 10 deletions(-)

Detailed changes

crates/language_models/src/provider/deepseek.rs

@@ -331,15 +331,25 @@ pub fn into_deepseek(
     for message in request.messages {
         for content in message.content {
             match content {
-                MessageContent::Text(text) => messages.push(match message.role {
-                    Role::User => deepseek::RequestMessage::User { content: text },
-                    Role::Assistant => deepseek::RequestMessage::Assistant {
-                        content: Some(text),
-                        tool_calls: Vec::new(),
-                        reasoning_content: current_reasoning.take(),
-                    },
-                    Role::System => deepseek::RequestMessage::System { content: text },
-                }),
+                MessageContent::Text(text) => {
+                    let should_add = if message.role == Role::User {
+                        !text.trim().is_empty()
+                    } else {
+                        !text.is_empty()
+                    };
+
+                    if should_add {
+                        messages.push(match message.role {
+                            Role::User => deepseek::RequestMessage::User { content: text },
+                            Role::Assistant => deepseek::RequestMessage::Assistant {
+                                content: Some(text),
+                                tool_calls: Vec::new(),
+                                reasoning_content: current_reasoning.take(),
+                            },
+                            Role::System => deepseek::RequestMessage::System { content: text },
+                        });
+                    }
+                }
                 MessageContent::Thinking { text, .. } => {
                     // Accumulate reasoning content for next assistant message
                     current_reasoning.get_or_insert_default().push_str(&text);
@@ -445,7 +455,9 @@ impl DeepSeekEventMapper {
         };
 
         let mut events = Vec::new();
-        if let Some(content) = choice.delta.content.clone() {
+        if let Some(content) = choice.delta.content.clone()
+            && !content.is_empty()
+        {
             events.push(Ok(LanguageModelCompletionEvent::Text(content)));
         }