refactor: move editing for ast using SyntaxEditor to a separate file

Signed-off-by: Tarek <[email protected]>

Author: tareknaser

crates/ide-assists/src/handlers/introduce_named_generic.rs

@@ -51,7 +51,7 @@ pub(crate) fn introduce_named_generic(acc: &mut Assists, ctx: &AssistContext<'_>
 
             editor.replace(impl_trait_type.syntax(), new_ty.syntax());
             let generic_param = syntax::ast::GenericParam::from(type_param);
-            fn_.syntax_editor_add_generic_param(&mut editor, generic_param.clone());
+            editor.syntax_editor_add_generic_param(fn_, generic_param.clone());
 
             if let Some(cap) = ctx.config.snippet_cap {
                 editor.add_annotation(generic_param.syntax(), builder.make_tabstop_before(cap));

crates/syntax/src/syntax_editor.rs

@@ -16,6 +16,7 @@ use rustc_hash::FxHashMap;
 use crate::{SyntaxElement, SyntaxNode, SyntaxToken};
 
 mod edit_algo;
+mod edits;
 mod mapping;
 
 pub use mapping::{SyntaxMapping, SyntaxMappingBuilder};

crates/syntax/src/syntax_editor/edits.rs

@@ -0,0 +1,72 @@
+//! Structural editing for ast using `SyntaxEditor`
+
+use crate::{
+    ast::make, ast::AstNode, ast::Fn, ast::GenericParam, ast::HasGenericParams, ast::HasName,
+    syntax_editor::Position, syntax_editor::SyntaxEditor, SyntaxKind,
+};
+
+impl SyntaxEditor {
+    /// Adds a new generic param to the function using `SyntaxEditor`
+    pub fn syntax_editor_add_generic_param(&mut self, function: Fn, new_param: GenericParam) {
+        match function.generic_param_list() {
+            Some(generic_param_list) => match generic_param_list.generic_params().last() {
+                Some(last_param) => {
+                    // There exists a generic param list and it's not empty
+                    let position = generic_param_list.r_angle_token().map_or_else(
+                        || Position::last_child_of(function.syntax()),
+                        Position::before,
+                    );
+
+                    if last_param
+                        .syntax()
+                        .next_sibling_or_token()
+                        .map_or(false, |it| it.kind() == SyntaxKind::COMMA)
+                    {
+                        self.insert(
+                            Position::after(last_param.syntax()),
+                            new_param.syntax().clone(),
+                        );
+                        self.insert(
+                            Position::after(last_param.syntax()),
+                            make::token(SyntaxKind::WHITESPACE),
+                        );
+                        self.insert(
+                            Position::after(last_param.syntax()),
+                            make::token(SyntaxKind::COMMA),
+                        );
+                    } else {
+                        let elements = vec![
+                            make::token(SyntaxKind::COMMA).into(),
+                            make::token(SyntaxKind::WHITESPACE).into(),
+                            new_param.syntax().clone().into(),
+                        ];
+                        self.insert_all(position, elements);
+                    }
+                }
+                None => {
+                    // There exists a generic param list but it's empty
+                    let position = Position::after(generic_param_list.l_angle_token().unwrap());
+                    self.insert(position, new_param.syntax());
+                }
+            },
+            None => {
+                // There was no generic param list
+                let position = if let Some(name) = function.name() {
+                    Position::after(name.syntax)
+                } else if let Some(fn_token) = function.fn_token() {
+                    Position::after(fn_token)
+                } else if let Some(param_list) = function.param_list() {
+                    Position::before(param_list.syntax)
+                } else {
+                    Position::last_child_of(function.syntax())
+                };
+                let elements = vec![
+                    make::token(SyntaxKind::L_ANGLE).into(),
+                    new_param.syntax().clone().into(),
+                    make::token(SyntaxKind::R_ANGLE).into(),
+                ];
+                self.insert_all(position, elements);
+            }
+        }
+    }
+}