Ollama max_tokens settings (#17025)

- Support `available_models` for Ollama
- Clamp default max tokens (context length) to 16384.
- Add documentation for ollama context configuration.

crates/language_model/src/provider/ollama.rs

@@ -6,8 +6,10 @@ use ollama::{
     get_models, preload_model, stream_chat_completion, ChatMessage, ChatOptions, ChatRequest,
     ChatResponseDelta, OllamaToolCall,
 };
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
 use settings::{Settings, SettingsStore};
-use std::{sync::Arc, time::Duration};
+use std::{collections::BTreeMap, sync::Arc, time::Duration};
 use ui::{prelude::*, ButtonLike, Indicator};
 use util::ResultExt;
 
@@ -28,6 +30,17 @@ const PROVIDER_NAME: &str = "Ollama";
 pub struct OllamaSettings {
     pub api_url: String,
     pub low_speed_timeout: Option<Duration>,
+    pub available_models: Vec<AvailableModel>,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, JsonSchema)]
+pub struct AvailableModel {
+    /// The model name in the Ollama API (e.g. "llama3.1:latest")
+    pub name: String,
+    /// The model's name in Zed's UI, such as in the model selector dropdown menu in the assistant panel.
+    pub display_name: Option<String>,
+    /// The Context Length parameter to the model (aka num_ctx or n_ctx)
+    pub max_tokens: usize,
 }
 
 pub struct OllamaLanguageModelProvider {
@@ -61,7 +74,7 @@ impl State {
                 // indicating which models are embedding models,
                 // simply filter out models with "-embed" in their name
                 .filter(|model| !model.name.contains("-embed"))
-                .map(|model| ollama::Model::new(&model.name))
+                .map(|model| ollama::Model::new(&model.name, None, None))
                 .collect();
 
             models.sort_by(|a, b| a.name.cmp(&b.name));
@@ -123,10 +136,32 @@ impl LanguageModelProvider for OllamaLanguageModelProvider {
     }
 
     fn provided_models(&self, cx: &AppContext) -> Vec<Arc<dyn LanguageModel>> {
-        self.state
-            .read(cx)
+        let mut models: BTreeMap<String, ollama::Model> = BTreeMap::default();
+
+        // Add models from the Ollama API
+        for model in self.state.read(cx).available_models.iter() {
+            models.insert(model.name.clone(), model.clone());
+        }
+
+        // Override with available models from settings
+        for model in AllLanguageModelSettings::get_global(cx)
+            .ollama
             .available_models
             .iter()
+        {
+            models.insert(
+                model.name.clone(),
+                ollama::Model {
+                    name: model.name.clone(),
+                    display_name: model.display_name.clone(),
+                    max_tokens: model.max_tokens,
+                    keep_alive: None,
+                },
+            );
+        }
+
+        models
+            .into_values()
             .map(|model| {
                 Arc::new(OllamaLanguageModel {
                     id: LanguageModelId::from(model.name.clone()),