add hover for builtin functions

Author: gerau

src/backend.rs

@@ -323,7 +323,23 @@ impl Backend {
                     range: Some(Range { start, end }),
                 })
             }
-            _ => None,
+            other => {
+                let template = completion::builtin::match_callname(other.to_owned())?;
+                let description = format!(
+                    "```simplicityhl\nfn {}({}) -> {}\n```\n{}",
+                    template.display_name,
+                    template.args.join(", "),
+                    template.return_type,
+                    template.description
+                );
+                Some(Hover {
+                    contents: tower_lsp_server::lsp_types::HoverContents::Markup(MarkupContent {
+                        kind: MarkupKind::Markdown,
+                        value: description,
+                    }),
+                    range: Some(Range { start, end }),
+                })
+            }
         }
     }
 }

src/completion/builtin.rs

@@ -50,7 +50,7 @@ pub fn get_builtin_functions() -> Vec<FunctionTemplate> {
         .collect()
 }
 
-fn match_callname(call: CallName) -> Option<FunctionTemplate> {
+pub fn match_callname(call: CallName) -> Option<FunctionTemplate> {
     match call {
         CallName::UnwrapLeft(aliased_type) => {
             let ty = aliased_type.to_string();
@@ -94,13 +94,13 @@ fn match_callname(call: CallName) -> Option<FunctionTemplate> {
         CallName::Assert => Some(FunctionTemplate::simple(
             "assert!",
             str_vec!["bool"],
-            "",
+            "()",
             "Fails program if argument is 'false'",
         )),
         CallName::Panic => Some(FunctionTemplate::simple(
             "panic!",
             str_vec![],
-            "",
+            "()",
             "Fails program",
         )),
         CallName::Debug => Some(FunctionTemplate::simple(