1 files changed, 229 insertions, 0 deletions

diff --git a/crates/ra_assists/src/ast_builder.rs b/crates/ra_assists/src/ast_builder.rs
new file mode 100644
index 000000000..e4ea1fca9
--- /dev/null
+++ b/crates/ra_assists/src/ast_builder.rs
@@ -0,0 +1,229 @@
+use itertools::Itertools;
+
+use hir::Name;
+use ra_syntax::{ast, AstNode, SourceFile};
+
+pub struct AstBuilder<N: AstNode> {
+    _phantom: std::marker::PhantomData<N>,
+}
+
+impl AstBuilder<ast::RecordField> {
+    pub fn from_name(name: &Name) -> ast::RecordField {
+        ast_node_from_file_text(&format!("fn f() {{ S {{ {}: (), }} }}", name))
+    }
+
+    fn from_text(text: &str) -> ast::RecordField {
+        ast_node_from_file_text(&format!("fn f() {{ S {{ {}, }} }}", text))
+    }
+
+    pub fn from_pieces(name: &ast::NameRef, expr: Option<&ast::Expr>) -> ast::RecordField {
+        match expr {
+            Some(expr) => Self::from_text(&format!("{}: {}", name.syntax(), expr.syntax())),
+            None => Self::from_text(&name.syntax().to_string()),
+        }
+    }
+}
+
+impl AstBuilder<ast::Block> {
+    fn from_text(text: &str) -> ast::Block {
+        ast_node_from_file_text(&format!("fn f() {}", text))
+    }
+
+    pub fn single_expr(e: &ast::Expr) -> ast::Block {
+        Self::from_text(&format!("{{ {} }}", e.syntax()))
+    }
+}
+
+impl AstBuilder<ast::Expr> {
+    fn from_text(text: &str) -> ast::Expr {
+        ast_node_from_file_text(&format!("const C: () = {};", text))
+    }
+
+    pub fn unit() -> ast::Expr {
+        Self::from_text("()")
+    }
+
+    pub fn unimplemented() -> ast::Expr {
+        Self::from_text("unimplemented!()")
+    }
+}
+
+impl AstBuilder<ast::NameRef> {
+    pub fn new(text: &str) -> ast::NameRef {
+        ast_node_from_file_text(&format!("fn f() {{ {}; }}", text))
+    }
+}
+
+impl AstBuilder<ast::Path> {
+    fn from_text(text: &str) -> ast::Path {
+        ast_node_from_file_text(text)
+    }
+
+    pub fn from_name(name: ast::Name) -> ast::Path {
+        let name = name.syntax().to_string();
+        Self::from_text(name.as_str())
+    }
+
+    pub fn from_pieces(enum_name: ast::Name, var_name: ast::Name) -> ast::Path {
+        Self::from_text(&format!("{}::{}", enum_name.syntax(), var_name.syntax()))
+    }
+}
+
+impl AstBuilder<ast::BindPat> {
+    fn from_text(text: &str) -> ast::BindPat {
+        ast_node_from_file_text(&format!("fn f({}: ())", text))
+    }
+
+    pub fn from_name(name: &ast::Name) -> ast::BindPat {
+        Self::from_text(name.text())
+    }
+}
+
+impl AstBuilder<ast::PlaceholderPat> {
+    fn from_text(text: &str) -> ast::PlaceholderPat {
+        ast_node_from_file_text(&format!("fn f({}: ())", text))
+    }
+
+    pub fn placeholder() -> ast::PlaceholderPat {
+        Self::from_text("_")
+    }
+}
+
+impl AstBuilder<ast::TupleStructPat> {
+    fn from_text(text: &str) -> ast::TupleStructPat {
+        ast_node_from_file_text(&format!("fn f({}: ())", text))
+    }
+
+    pub fn from_pieces(
+        path: &ast::Path,
+        pats: impl Iterator<Item = ast::Pat>,
+    ) -> ast::TupleStructPat {
+        let pats_str = pats.map(|p| p.syntax().to_string()).collect::<Vec<_>>().join(", ");
+        Self::from_text(&format!("{}({})", path.syntax(), pats_str))
+    }
+}
+
+impl AstBuilder<ast::RecordPat> {
+    fn from_text(text: &str) -> ast::RecordPat {
+        ast_node_from_file_text(&format!("fn f({}: ())", text))
+    }
+
+    pub fn from_pieces(path: &ast::Path, pats: impl Iterator<Item = ast::Pat>) -> ast::RecordPat {
+        let pats_str = pats.map(|p| p.syntax().to_string()).collect::<Vec<_>>().join(", ");
+        Self::from_text(&format!("{}{{ {} }}", path.syntax(), pats_str))
+    }
+}
+
+impl AstBuilder<ast::PathPat> {
+    fn from_text(text: &str) -> ast::PathPat {
+        ast_node_from_file_text(&format!("fn f({}: ())", text))
+    }
+
+    pub fn from_path(path: &ast::Path) -> ast::PathPat {
+        let path_str = path.syntax().text().to_string();
+        Self::from_text(path_str.as_str())
+    }
+}
+
+impl AstBuilder<ast::MatchArm> {
+    fn from_text(text: &str) -> ast::MatchArm {
+        ast_node_from_file_text(&format!("fn f() {{ match () {{{}}} }}", text))
+    }
+
+    pub fn from_pieces(pats: impl Iterator<Item = ast::Pat>, expr: &ast::Expr) -> ast::MatchArm {
+        let pats_str = pats.map(|p| p.syntax().to_string()).join(" | ");
+        Self::from_text(&format!("{} => {}", pats_str, expr.syntax()))
+    }
+}
+
+impl AstBuilder<ast::MatchArmList> {
+    fn from_text(text: &str) -> ast::MatchArmList {
+        ast_node_from_file_text(&format!("fn f() {{ match () {{{}}} }}", text))
+    }
+
+    pub fn from_arms(arms: impl Iterator<Item = ast::MatchArm>) -> ast::MatchArmList {
+        let arms_str = arms.map(|arm| format!("\n    {}", arm.syntax())).join(",");
+        Self::from_text(&format!("{},\n", arms_str))
+    }
+}
+
+impl AstBuilder<ast::WherePred> {
+    fn from_text(text: &str) -> ast::WherePred {
+        ast_node_from_file_text(&format!("fn f() where {} {{ }}", text))
+    }
+
+    pub fn from_pieces(
+        path: ast::Path,
+        bounds: impl Iterator<Item = ast::TypeBound>,
+    ) -> ast::WherePred {
+        let bounds = bounds.map(|b| b.syntax().to_string()).collect::<Vec<_>>().join(" + ");
+        Self::from_text(&format!("{}: {}", path.syntax(), bounds))
+    }
+}
+
+impl AstBuilder<ast::WhereClause> {
+    fn from_text(text: &str) -> ast::WhereClause {
+        ast_node_from_file_text(&format!("fn f() where {} {{ }}", text))
+    }
+
+    pub fn from_predicates(preds: impl Iterator<Item = ast::WherePred>) -> ast::WhereClause {
+        let preds = preds.map(|p| p.syntax().to_string()).collect::<Vec<_>>().join(", ");
+        Self::from_text(preds.as_str())
+    }
+}
+
+fn ast_node_from_file_text<N: AstNode>(text: &str) -> N {
+    let parse = SourceFile::parse(text);
+    let res = parse.tree().syntax().descendants().find_map(N::cast).unwrap();
+    res
+}
+
+pub(crate) mod tokens {
+    use once_cell::sync::Lazy;
+    use ra_syntax::{AstNode, Parse, SourceFile, SyntaxKind::*, SyntaxToken, T};
+
+    static SOURCE_FILE: Lazy<Parse<SourceFile>> = Lazy::new(|| SourceFile::parse(",\n; ;"));
+
+    pub(crate) fn comma() -> SyntaxToken {
+        SOURCE_FILE
+            .tree()
+            .syntax()
+            .descendants_with_tokens()
+            .filter_map(|it| it.into_token())
+            .find(|it| it.kind() == T![,])
+            .unwrap()
+    }
+
+    pub(crate) fn single_space() -> SyntaxToken {
+        SOURCE_FILE
+            .tree()
+            .syntax()
+            .descendants_with_tokens()
+            .filter_map(|it| it.into_token())
+            .find(|it| it.kind() == WHITESPACE && it.text().as_str() == " ")
+            .unwrap()
+    }
+
+    #[allow(unused)]
+    pub(crate) fn single_newline() -> SyntaxToken {
+        SOURCE_FILE
+            .tree()
+            .syntax()
+            .descendants_with_tokens()
+            .filter_map(|it| it.into_token())
+            .find(|it| it.kind() == WHITESPACE && it.text().as_str() == "\n")
+            .unwrap()
+    }
+
+    pub(crate) struct WsBuilder(SourceFile);
+
+    impl WsBuilder {
+        pub(crate) fn new(text: &str) -> WsBuilder {
+            WsBuilder(SourceFile::parse(text).ok().unwrap())
+        }
+        pub(crate) fn ws(&self) -> SyntaxToken {
+            self.0.syntax().first_child_or_token().unwrap().into_token().unwrap()
+        }
+    }
+
+}