add clippy warning for string_slice (#5422)

Co-authored-by: Douwe Osinga <douwe@squareup.com>

crates/goose-cli/src/session/completion.rs

@@ -26,7 +26,7 @@ impl GooseCompleter {
     /// Complete prompt names for the /prompt command
     fn complete_prompt_names(&self, line: &str) -> Result<(usize, Vec<Pair>)> {
         // Get the prefix of the prompt name being typed
-        let prefix = if line.len() > 8 { &line[8..] } else { "" };
+        let prefix = line.get(8..).unwrap_or("");
 
         // Get available prompts from cache
         let cache = self.completion_cache.read().unwrap();
@@ -156,7 +156,7 @@ impl GooseCompleter {
 
     /// Complete argument keys for a specific prompt
     fn complete_argument_keys(&self, line: &str) -> Result<(usize, Vec<Pair>)> {
-        let parts: Vec<&str> = line[8..].split_whitespace().collect();
+        let parts: Vec<&str> = line.get(8..).unwrap_or("").split_whitespace().collect();
 
         // We need at least the prompt name
         if parts.is_empty() {

crates/goose-cli/src/session/input.rs

@@ -169,15 +169,17 @@ fn handle_slash_command(input: &str) -> Option<InputResult> {
             }
         }
         s if s.starts_with(CMD_EXTENSION) => Some(InputResult::AddExtension(
-            s[CMD_EXTENSION.len()..].to_string(),
+            s.get(CMD_EXTENSION.len()..).unwrap_or("").to_string(),
         )),
-        s if s.starts_with(CMD_BUILTIN) => {
-            Some(InputResult::AddBuiltin(s[CMD_BUILTIN.len()..].to_string()))
+        s if s.starts_with(CMD_BUILTIN) => Some(InputResult::AddBuiltin(
+            s.get(CMD_BUILTIN.len()..).unwrap_or("").to_string(),
+        )),
+        s if s.starts_with(CMD_MODE) => Some(InputResult::GooseMode(
+            s.get(CMD_MODE.len()..).unwrap_or("").to_string(),
+        )),
+        s if s.starts_with(CMD_PLAN) => {
+            parse_plan_command(s.get(CMD_PLAN.len()..).unwrap_or("").trim().to_string())
         }
-        s if s.starts_with(CMD_MODE) => {
-            Some(InputResult::GooseMode(s[CMD_MODE.len()..].to_string()))
-        }
-        s if s.starts_with(CMD_PLAN) => parse_plan_command(s[CMD_PLAN.len()..].trim().to_string()),
         s if s == CMD_ENDPLAN => Some(InputResult::EndPlan),
         s if s == CMD_CLEAR => Some(InputResult::Clear),
         s if s.starts_with(CMD_RECIPE) => parse_recipe_command(s),
@@ -199,7 +201,7 @@ fn parse_recipe_command(s: &str) -> Option<InputResult> {
     }
 
     // Extract the filepath from the command
-    let filepath = s[CMD_RECIPE.len()..].trim();
+    let filepath = s.get(CMD_RECIPE.len()..).unwrap_or("").trim();
 
     if filepath.is_empty() {
         return Some(InputResult::Recipe(None));