WIP: Add create_function assist

Author: TimoFreiberg

crates/ra_assists/src/handlers/add_function.rs

@@ -0,0 +1,384 @@
+use ra_syntax::{
+    ast::{self, AstNode},
+    SmolStr, SyntaxKind, SyntaxNode, TextUnit,
+};
+
+use crate::{Assist, AssistCtx, AssistId};
+use ast::{CallExpr, Expr};
+use hir::ModuleDef;
+use ra_fmt::leading_indent;
+
+// Assist: add_function
+//
+// Adds a stub function with a signature matching the function under the cursor.
+//
+// ```
+// fn foo() {
+//      bar<|>("", baz());
+// }
+//
+// ```
+// ->
+// ```
+// fn foo() {
+//      bar("", baz());
+// }
+//
+// fn bar(arg_1: &str, baz: Baz) {
+//      todo!();
+// }
+//
+// ```
+pub(crate) fn add_function(ctx: AssistCtx) -> Option<Assist> {
+    let path: ast::Path = ctx.find_node_at_offset()?;
+
+    if ctx.sema.resolve_path(&path).is_some() {
+        // The function call already resolves, no need to add a function
+        return None;
+    }
+
+    if path.qualifier().is_some() {
+        return None;
+    }
+
+    let call: ast::CallExpr = ctx.find_node_at_offset()?;
+
+    if unresolved_path_is_not_call_expr(&path, &call)? {
+        return None;
+    }
+
+    let function_builder = FunctionBuilder::from_call(&ctx, &call)?;
+
+    ctx.add_assist(AssistId("add_function"), "Add function", |edit| {
+        edit.target(call.syntax().text_range());
+
+        let function_template = function_builder.render();
+        edit.set_cursor(function_template.cursor_offset);
+        edit.insert(function_template.insert_offset, function_template.fn_text);
+    })
+}
+
+/// Checks whether the path of the called function in `call_expr` equals `path`.
+///
+/// If it doesn't, the cursor is on an unresolved path of a non-function item in
+/// `call_expr` and we don't want to generate a function with that item's name.
+fn unresolved_path_is_not_call_expr(path: &ast::Path, call_expr: &ast::CallExpr) -> Option<bool> {
+    let call_path = call_expr.syntax().descendants().find_map(ast::Path::cast)?;
+    Some(call_path != *path)
+}
+
+struct FunctionTemplate {
+    insert_offset: TextUnit,
+    cursor_offset: TextUnit,
+    fn_text: String,
+}
+
+struct FunctionBuilder {
+    start_offset: TextUnit,
+    fn_name: String,
+    fn_generics: String,
+    fn_args: String,
+    indent: String,
+}
+
+impl FunctionBuilder {
+    fn from_call(ctx: &AssistCtx, call: &ast::CallExpr) -> Option<Self> {
+        let (start, indent) = next_space_for_fn(&call)?;
+        let fn_name = fn_name(&call)?;
+        let fn_generics = fn_generics(&call)?;
+        let fn_args = fn_args(ctx, &call)?;
+        let indent = if let Some(i) = &indent { i.to_string() } else { String::new() };
+        Some(Self { start_offset: start, fn_name, fn_generics, fn_args, indent })
+    }
+    fn render(&self) -> FunctionTemplate {
+        let mut fn_buf = String::with_capacity(128);
+        fn_buf.push_str("\n\n");
+        fn_buf.push_str(&self.indent);
+        fn_buf.push_str("fn ");
+        fn_buf.push_str(&self.fn_name);
+        fn_buf.push_str(&self.fn_generics);
+        fn_buf.push_str(&self.fn_args);
+        fn_buf.push_str(" {\n");
+        fn_buf.push_str(&self.indent);
+        fn_buf.push_str("    ");
+
+        // We take the offset here to put the cursor in front of the `todo` body
+        let offset = TextUnit::of_str(&fn_buf);
+
+        fn_buf.push_str("todo!()\n");
+        fn_buf.push_str(&self.indent);
+        fn_buf.push_str("}");
+
+        let cursor_pos = self.start_offset + offset;
+        FunctionTemplate {
+            fn_text: fn_buf,
+            cursor_offset: cursor_pos,
+            insert_offset: self.start_offset,
+        }
+    }
+}
+
+impl FunctionTemplate {}
+
+fn fn_name(call: &CallExpr) -> Option<String> {
+    Some(call.expr()?.syntax().to_string())
+}
+
+fn fn_generics(_call: &CallExpr) -> Option<String> {
+    // TODO
+    Some("".into())
+}
+
+fn fn_args(ctx: &AssistCtx, _call: &CallExpr) -> Option<String> {
+    let arg_list = _call.syntax().descendants().find_map(ast::ArgList::cast)?;
+    for arg in arg_list.args() {
+        match &arg {
+            Expr::CallExpr(call_expr) => {
+                arg_for_call(ctx, call_expr);
+            }
+            _ => {}
+        }
+        dbg!(&arg);
+    }
+    Some("()".into())
+}
+
+fn arg_for_call(ctx: &AssistCtx, call_expr: &CallExpr) -> Option<String> {
+    let path = call_expr.syntax().descendants().find_map(ast::Path::cast)?;
+    let type_string = match ctx.sema.resolve_path(&path)? {
+        hir::PathResolution::Def(ModuleDef::Function(f)) => {
+            let _ret_type = dbg!(f.ret_type(ctx.sema.db));
+            // TODO: find out how to print this
+            String::new()
+        }
+        _ => return None,
+    };
+
+    Some(format!("arg: {}", type_string))
+}
+
+/// Returns the position inside the current mod or file
+/// directly after the current block
+/// We want to write the generated function directly after
+/// fns, impls or macro calls, but inside mods
+fn next_space_for_fn(expr: &CallExpr) -> Option<(TextUnit, Option<SmolStr>)> {
+    let mut ancestors = expr.syntax().ancestors().peekable();
+    let mut last_ancestor: Option<SyntaxNode> = None;
+    while let Some(next_ancestor) = ancestors.next() {
+        match next_ancestor.kind() {
+            SyntaxKind::SOURCE_FILE => {
+                break;
+            }
+            SyntaxKind::ITEM_LIST => {
+                if ancestors.peek().map(|a| a.kind()) == Some(SyntaxKind::MODULE) {
+                    break;
+                }
+            }
+            _ => {}
+        }
+        last_ancestor = Some(next_ancestor);
+    }
+    last_ancestor.map(|a| (a.text_range().end(), leading_indent(&a)))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::helpers::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn add_function_with_no_args() {
+        check_assist(
+            add_function,
+            r"
+fn foo() {
+    bar<|>();
+}
+",
+            r"
+fn foo() {
+    bar();
+}
+
+fn bar() {
+    <|>todo!()
+}
+",
+        )
+    }
+
+    #[test]
+    fn add_function_from_method() {
+        // This ensures that the function is correctly generated
+        // in the next outer mod or file
+        check_assist(
+            add_function,
+            r"
+impl Foo {
+    fn foo() {
+        bar<|>();
+    }
+}
+",
+            r"
+impl Foo {
+    fn foo() {
+        bar();
+    }
+}
+
+fn bar() {
+    <|>todo!()
+}
+",
+        )
+    }
+
+    #[test]
+    fn add_function_directly_after_current_block() {
+        // The new fn should not be created at the end of the file or module
+        check_assist(
+            add_function,
+            r"
+fn foo1() {
+    bar<|>();
+}
+
+fn foo2() {}
+",
+            r"
+fn foo1() {
+    bar();
+}
+
+fn bar() {
+    <|>todo!()
+}
+
+fn foo2() {}
+",
+        )
+    }
+
+    #[test]
+    fn add_function_with_no_args_in_same_module() {
+        check_assist(
+            add_function,
+            r"
+mod baz {
+    fn foo() {
+        bar<|>();
+    }
+}
+",
+            r"
+mod baz {
+    fn foo() {
+        bar();
+    }
+
+    fn bar() {
+        <|>todo!()
+    }
+}
+",
+        )
+    }
+
+    #[test]
+    fn add_function_with_function_call_arg() {
+        check_assist(
+            add_function,
+            r"
+fn baz() -> Baz { todo!() }
+fn foo() {
+    bar<|>(baz());
+}
+",
+            r"
+fn baz() -> Baz { todo!() }
+fn foo() {
+    bar(baz());
+}
+
+fn bar(baz: Baz) {
+    <|>todo!()
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_function_not_applicable_if_function_already_exists() {
+        check_assist_not_applicable(
+            add_function,
+            r"
+fn foo() {
+    bar<|>();
+}
+
+fn bar() {}
+",
+        )
+    }
+
+    #[test]
+    fn add_function_not_applicable_if_unresolved_variable_in_call_is_selected() {
+        check_assist_not_applicable(
+            // bar is resolved, but baz isn't.
+            // The assist is only active if the cursor is on an unresolved path,
+            // but the assist should only be offered if the path is a function call.
+            add_function,
+            r"
+fn foo() {
+    bar(b<|>az);
+}
+
+fn bar(baz: ()) {}
+",
+        )
+    }
+
+    #[test]
+    fn add_function_not_applicable_if_function_path_not_singleton() {
+        // In the future this assist could be extended to generate functions
+        // if the path is in the same crate (or even the same workspace).
+        // For the beginning, I think this is fine.
+        check_assist_not_applicable(
+            add_function,
+            r"
+fn foo() {
+    other_crate::bar<|>();
+}
+        ",
+        )
+    }
+
+    #[test]
+    #[ignore]
+    fn create_method_with_no_args() {
+        check_assist(
+            add_function,
+            r"
+struct Foo;
+impl Foo {
+    fn foo(&self) {
+        self.bar()<|>;
+    }
+}
+        ",
+            r"
+struct Foo;
+impl Foo {
+    fn foo(&self) {
+        self.bar();
+    }
+    fn bar(&self) {
+        todo!();
+    }
+}
+        ",
+        )
+    }
+}