6 files changed, 125 insertions, 20 deletions

diff --git a/crates/syntax/src/ast/edit.rs b/crates/syntax/src/ast/edit.rs
index 060b20966..dda0a0319 100644
--- a/crates/syntax/src/ast/edit.rs
+++ b/crates/syntax/src/ast/edit.rs
@@ -13,7 +13,7 @@ use crate::{
     ast::{
         self,
         make::{self, tokens},
-        AstNode, TypeBoundsOwner,
+        AstNode, GenericParamsOwner, NameOwner, TypeBoundsOwner,
     },
     AstToken, Direction, InsertPosition, SmolStr, SyntaxElement, SyntaxKind,
     SyntaxKind::{ATTR, COMMENT, WHITESPACE},
@@ -46,6 +46,19 @@ impl ast::Fn {
         to_insert.push(body.syntax().clone().into());
         self.replace_children(single_node(old_body_or_semi), to_insert)
     }
+
+    #[must_use]
+    pub fn with_generic_param_list(&self, generic_args: ast::GenericParamList) -> ast::Fn {
+        if let Some(old) = self.generic_param_list() {
+            return self.replace_descendant(old, generic_args);
+        }
+
+        let anchor = self.name().expect("The function must have a name").syntax().clone();
+
+        let mut to_insert: ArrayVec<[SyntaxElement; 1]> = ArrayVec::new();
+        to_insert.push(generic_args.syntax().clone().into());
+        self.insert_children(InsertPosition::After(anchor.into()), to_insert)
+    }
 }
 
 fn make_multiline<N>(node: N) -> N
@@ -80,6 +93,22 @@ where
     }
 }
 
+impl ast::Impl {
+    #[must_use]
+    pub fn with_assoc_item_list(&self, items: ast::AssocItemList) -> ast::Impl {
+        let mut to_insert: ArrayVec<[SyntaxElement; 2]> = ArrayVec::new();
+        if let Some(old_items) = self.assoc_item_list() {
+            let to_replace: SyntaxElement = old_items.syntax().clone().into();
+            to_insert.push(items.syntax().clone().into());
+            self.replace_children(single_node(to_replace), to_insert)
+        } else {
+            to_insert.push(make::tokens::single_space().into());
+            to_insert.push(items.syntax().clone().into());
+            self.insert_children(InsertPosition::Last, to_insert)
+        }
+    }
+}
+
 impl ast::AssocItemList {
     #[must_use]
     pub fn append_items(
@@ -260,16 +289,16 @@ impl ast::Path {
 
 impl ast::PathSegment {
     #[must_use]
-    pub fn with_type_args(&self, type_args: ast::GenericArgList) -> ast::PathSegment {
-        self._with_type_args(type_args, false)
+    pub fn with_generic_args(&self, type_args: ast::GenericArgList) -> ast::PathSegment {
+        self._with_generic_args(type_args, false)
     }
 
     #[must_use]
     pub fn with_turbo_fish(&self, type_args: ast::GenericArgList) -> ast::PathSegment {
-        self._with_type_args(type_args, true)
+        self._with_generic_args(type_args, true)
     }
 
-    fn _with_type_args(&self, type_args: ast::GenericArgList, turbo: bool) -> ast::PathSegment {
+    fn _with_generic_args(&self, type_args: ast::GenericArgList, turbo: bool) -> ast::PathSegment {
         if let Some(old) = self.generic_arg_list() {
             return self.replace_children(
                 single_node(old.syntax().clone()),
@@ -334,6 +363,7 @@ impl ast::UseTree {
         self.clone()
     }
 
+    /// Splits off the given prefix, making it the path component of the use tree, appending the rest of the path to all UseTreeList items.
     #[must_use]
     pub fn split_prefix(&self, prefix: &ast::Path) -> ast::UseTree {
         let suffix = if self.path().as_ref() == Some(prefix) && self.use_tree_list().is_none() {
@@ -459,6 +489,61 @@ impl ast::MatchArmList {
     }
 }
 
+impl ast::GenericParamList {
+    #[must_use]
+    pub fn append_params(
+        &self,
+        params: impl IntoIterator<Item = ast::GenericParam>,
+    ) -> ast::GenericParamList {
+        let mut res = self.clone();
+        params.into_iter().for_each(|it| res = res.append_param(it));
+        res
+    }
+
+    #[must_use]
+    pub fn append_param(&self, item: ast::GenericParam) -> ast::GenericParamList {
+        let space = tokens::single_space();
+
+        let mut to_insert: ArrayVec<[SyntaxElement; 4]> = ArrayVec::new();
+        if self.generic_params().next().is_some() {
+            to_insert.push(space.into());
+        }
+        to_insert.push(item.syntax().clone().into());
+
+        macro_rules! after_l_angle {
+            () => {{
+                let anchor = match self.l_angle_token() {
+                    Some(it) => it.into(),
+                    None => return self.clone(),
+                };
+                InsertPosition::After(anchor)
+            }};
+        }
+
+        macro_rules! after_field {
+            ($anchor:expr) => {
+                if let Some(comma) = $anchor
+                    .syntax()
+                    .siblings_with_tokens(Direction::Next)
+                    .find(|it| it.kind() == T![,])
+                {
+                    InsertPosition::After(comma)
+                } else {
+                    to_insert.insert(0, make::token(T![,]).into());
+                    InsertPosition::After($anchor.syntax().clone().into())
+                }
+            };
+        };
+
+        let position = match self.generic_params().last() {
+            Some(it) => after_field!(it),
+            None => after_l_angle!(),
+        };
+
+        self.insert_children(position, to_insert)
+    }
+}
+
 #[must_use]
 pub fn remove_attrs_and_docs<N: ast::AttrsOwner>(node: &N) -> N {
     N::cast(remove_attrs_and_docs_inner(node.syntax().clone())).unwrap()
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 7ba625990..4a0ffcbb0 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -21,6 +21,10 @@ pub fn ty(text: &str) -> ast::Type {
     ast_from_text(&format!("impl {} for D {{}};", text))
 }
 
+pub fn assoc_item_list() -> ast::AssocItemList {
+    ast_from_text("impl C for D {};")
+}
+
 pub fn path_segment(name_ref: ast::NameRef) -> ast::PathSegment {
     ast_from_text(&format!("use {};", name_ref))
 }
@@ -33,10 +37,15 @@ pub fn path_unqualified(segment: ast::PathSegment) -> ast::Path {
 pub fn path_qualified(qual: ast::Path, segment: ast::PathSegment) -> ast::Path {
     path_from_text(&format!("{}::{}", qual, segment))
 }
+// FIXME: make this private
 pub fn path_from_text(text: &str) -> ast::Path {
     ast_from_text(text)
 }
 
+pub fn glob_use_tree() -> ast::UseTree {
+    ast_from_text("use *;")
+}
+
 pub fn use_tree(
     path: ast::Path,
     use_tree_list: Option<ast::UseTreeList>,
@@ -144,10 +153,6 @@ fn expr_from_text(text: &str) -> ast::Expr {
     ast_from_text(&format!("const C: () = {};", text))
 }
 
-pub fn try_expr_from_text(text: &str) -> Option<ast::Expr> {
-    try_ast_from_text(&format!("const C: () = {};", text))
-}
-
 pub fn condition(expr: ast::Expr, pattern: Option<ast::Pat>) -> ast::Condition {
     match pattern {
         None => ast_from_text(&format!("const _: () = while {} {{}};", expr)),
@@ -297,6 +302,21 @@ pub fn param_list(pats: impl IntoIterator<Item = ast::Param>) -> ast::ParamList
     ast_from_text(&format!("fn f({}) {{ }}", args))
 }
 
+pub fn generic_param(name: String, ty: Option<ast::TypeBoundList>) -> ast::GenericParam {
+    let bound = match ty {
+        Some(it) => format!(": {}", it),
+        None => String::new(),
+    };
+    ast_from_text(&format!("fn f<{}{}>() {{ }}", name, bound))
+}
+
+pub fn generic_param_list(
+    pats: impl IntoIterator<Item = ast::GenericParam>,
+) -> ast::GenericParamList {
+    let args = pats.into_iter().join(", ");
+    ast_from_text(&format!("fn f<{}>() {{ }}", args))
+}
+
 pub fn visibility_pub_crate() -> ast::Visibility {
     ast_from_text("pub(crate) struct S")
 }
@@ -332,16 +352,6 @@ fn ast_from_text<N: AstNode>(text: &str) -> N {
     node
 }
 
-fn try_ast_from_text<N: AstNode>(text: &str) -> Option<N> {
-    let parse = SourceFile::parse(text);
-    let node = parse.tree().syntax().descendants().find_map(N::cast)?;
-    let node = node.syntax().clone();
-    let node = unroot(node);
-    let node = N::cast(node).unwrap();
-    assert_eq!(node.syntax().text_range().start(), 0.into());
-    Some(node)
-}
-
 fn unroot(n: SyntaxNode) -> SyntaxNode {
     SyntaxNode::new_root(n.green().clone())
 }
@@ -352,7 +362,7 @@ pub mod tokens {
     use crate::{ast, AstNode, Parse, SourceFile, SyntaxKind::*, SyntaxToken};
 
     pub(super) static SOURCE_FILE: Lazy<Parse<SourceFile>> =
-        Lazy::new(|| SourceFile::parse("const C: <()>::Item = (1 != 1, 2 == 2, !true)\n;"));
+        Lazy::new(|| SourceFile::parse("const C: <()>::Item = (1 != 1, 2 == 2, !true)\n;\n\n"));
 
     pub fn single_space() -> SyntaxToken {
         SOURCE_FILE
@@ -392,6 +402,16 @@ pub mod tokens {
             .unwrap()
     }
 
+    pub fn blank_line() -> SyntaxToken {
+        SOURCE_FILE
+            .tree()
+            .syntax()
+            .descendants_with_tokens()
+            .filter_map(|it| it.into_token())
+            .find(|it| it.kind() == WHITESPACE && it.text().as_str() == "\n\n")
+            .unwrap()
+    }
+
     pub struct WsBuilder(SourceFile);
 
     impl WsBuilder {
diff --git a/crates/syntax/test_data/parser/inline/ok/0102_record_field_pat_list.rast b/crates/syntax/test_data/parser/inline/ok/0102_record_pat_field_list.rast
index 866e60ed8..866e60ed8 100644
--- a/crates/syntax/test_data/parser/inline/ok/0102_record_field_pat_list.rast
+++ b/crates/syntax/test_data/parser/inline/ok/0102_record_pat_field_list.rast
diff --git a/crates/syntax/test_data/parser/inline/ok/0102_record_field_pat_list.rs b/crates/syntax/test_data/parser/inline/ok/0102_record_pat_field_list.rs
index da3412fa8..da3412fa8 100644
--- a/crates/syntax/test_data/parser/inline/ok/0102_record_field_pat_list.rs
+++ b/crates/syntax/test_data/parser/inline/ok/0102_record_pat_field_list.rs
diff --git a/crates/syntax/test_data/parser/inline/ok/0145_record_field_pat.rast b/crates/syntax/test_data/parser/inline/ok/0145_record_pat_field.rast
index 925409bdf..925409bdf 100644
--- a/crates/syntax/test_data/parser/inline/ok/0145_record_field_pat.rast
+++ b/crates/syntax/test_data/parser/inline/ok/0145_record_pat_field.rast
diff --git a/crates/syntax/test_data/parser/inline/ok/0145_record_field_pat.rs b/crates/syntax/test_data/parser/inline/ok/0145_record_pat_field.rs
index 26b1d5f89..26b1d5f89 100644
--- a/crates/syntax/test_data/parser/inline/ok/0145_record_field_pat.rs
+++ b/crates/syntax/test_data/parser/inline/ok/0145_record_pat_field.rs