google_ai: Add Gemini 2.0 Flash support (#22665)

Release Notes:

- Added support for Google's Gemini 2.0 Flash experimental model.

Note:

Weirdly enough the model is slow on small talk responses like 'hi' (in
my tests) but very fast on things that need more tokens like 'write me a
snake game in python'. Likely an API problem.

TESTED ONLY ON WINDOWS! Would test further but don't have Linux
installed and don't have an Mac. Will likely work everywhere.

Why?:

I think Gemini 2.0 Flash is incredibly good model at coding and
following instructions. I think it would be nice to have it in the
editor. I did as minimal changes as possible while adding the model and
streaming validation. I think it's worth merging the commits as they
bring good improvements.

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/google_ai/src/google_ai.rs

@@ -1,6 +1,6 @@
 mod supported_countries;
 
-use anyhow::{anyhow, Result};
+use anyhow::{anyhow, bail, Result};
 use futures::{io::BufReader, stream::BoxStream, AsyncBufReadExt, AsyncReadExt, Stream, StreamExt};
 use http_client::{AsyncBody, HttpClient, Method, Request as HttpRequest};
 use serde::{Deserialize, Serialize};
@@ -15,6 +15,20 @@ pub async fn stream_generate_content(
     api_key: &str,
     mut request: GenerateContentRequest,
 ) -> Result<BoxStream<'static, Result<GenerateContentResponse>>> {
+    if request.contents.is_empty() {
+        bail!("Request must contain at least one content item");
+    }
+
+    if let Some(user_content) = request
+        .contents
+        .iter()
+        .find(|content| content.role == Role::User)
+    {
+        if user_content.parts.is_empty() {
+            bail!("User content must contain at least one part");
+        }
+    }
+
     let uri = format!(
         "{api_url}/v1beta/models/{model}:streamGenerateContent?alt=sse&key={api_key}",
         model = request.model
@@ -140,7 +154,7 @@ pub struct Content {
     pub role: Role,
 }
 
-#[derive(Debug, Deserialize, Serialize)]
+#[derive(Debug, PartialEq, Deserialize, Serialize)]
 #[serde(rename_all = "camelCase")]
 pub enum Role {
     User,
@@ -291,6 +305,8 @@ pub enum Model {
     Gemini15Pro,
     #[serde(rename = "gemini-1.5-flash")]
     Gemini15Flash,
+    #[serde(rename = "gemini-2.0-flash-exp")]
+    Gemini20Flash,
     #[serde(rename = "custom")]
     Custom {
         name: String,
@@ -305,6 +321,7 @@ impl Model {
         match self {
             Model::Gemini15Pro => "gemini-1.5-pro",
             Model::Gemini15Flash => "gemini-1.5-flash",
+            Model::Gemini20Flash => "gemini-2.0-flash-exp",
             Model::Custom { name, .. } => name,
         }
     }
@@ -313,6 +330,7 @@ impl Model {
         match self {
             Model::Gemini15Pro => "Gemini 1.5 Pro",
             Model::Gemini15Flash => "Gemini 1.5 Flash",
+            Model::Gemini20Flash => "Gemini 2.0 Flash",
             Self::Custom {
                 name, display_name, ..
             } => display_name.as_ref().unwrap_or(name),
@@ -323,6 +341,7 @@ impl Model {
         match self {
             Model::Gemini15Pro => 2_000_000,
             Model::Gemini15Flash => 1_000_000,
+            Model::Gemini20Flash => 1_000_000,
             Model::Custom { max_tokens, .. } => *max_tokens,
         }
     }

crates/language_model/src/model/cloud_model.rs

@@ -88,6 +88,7 @@ impl CloudModel {
             Self::Google(model) => match model {
                 google_ai::Model::Gemini15Pro
                 | google_ai::Model::Gemini15Flash
+                | google_ai::Model::Gemini20Flash
                 | google_ai::Model::Custom { .. } => {
                     LanguageModelAvailability::RequiresPlan(Plan::ZedPro)
                 }