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-rw-r--r--crates/ra_syntax/src/lib.rs173
1 files changed, 173 insertions, 0 deletions
diff --git a/crates/ra_syntax/src/lib.rs b/crates/ra_syntax/src/lib.rs
index dc4b779e8..e7d402446 100644
--- a/crates/ra_syntax/src/lib.rs
+++ b/crates/ra_syntax/src/lib.rs
@@ -14,6 +14,8 @@
14//! CST). The actual parser live in a separate `ra_parser` crate, thought the 14//! CST). The actual parser live in a separate `ra_parser` crate, thought the
15//! lexer lives in this crate. 15//! lexer lives in this crate.
16//! 16//!
17//! See `api_walkthrough` test in this file for a quick API tour!
18//!
17//! [RFC]: <https://github.com/rust-lang/rfcs/pull/2256> 19//! [RFC]: <https://github.com/rust-lang/rfcs/pull/2256>
18//! [Swift]: <https://github.com/apple/swift/blob/13d593df6f359d0cb2fc81cfaac273297c539455/lib/Syntax/README.md> 20//! [Swift]: <https://github.com/apple/swift/blob/13d593df6f359d0cb2fc81cfaac273297c539455/lib/Syntax/README.md>
19 21
@@ -87,3 +89,174 @@ pub fn check_fuzz_invariants(text: &str) {
87 validation::validate_block_structure(root); 89 validation::validate_block_structure(root);
88 let _ = file.errors(); 90 let _ = file.errors();
89} 91}
92
93/// This test does not assert anything and instead just shows off the crate's
94/// API.
95#[test]
96fn api_walkthrough() {
97 use ast::{ModuleItemOwner, NameOwner};
98
99 let source_code = "
100 fn foo() {
101 1 + 1
102 }
103 ";
104 // `SourceFile` is the main entry point.
105 //
106 // Note how `parse` does not return a `Result`: even completely invalid
107 // source code might be parsed.
108 let file = SourceFile::parse(source_code);
109
110 // Due to the way ownership is set up, owned syntax Nodes always live behind
111 // a `TreeArc` smart pointer. `TreeArc` is roughly an `std::sync::Arc` which
112 // points to the whole file instead of an individual node.
113 let file: TreeArc<SourceFile> = file;
114
115 // `SourceFile` is the root of the syntax tree. We can iterate file's items:
116 let mut func = None;
117 for item in file.items() {
118 match item.kind() {
119 ast::ModuleItemKind::FnDef(f) => func = Some(f),
120 _ => unreachable!(),
121 }
122 }
123 // The returned items are always references.
124 let func: &ast::FnDef = func.unwrap();
125
126 // All nodes implement `ToOwned` trait, with `Owned = TreeArc<Self>`.
127 // `to_owned` is a cheap operation: atomic increment.
128 let _owned_func: TreeArc<ast::FnDef> = func.to_owned();
129
130 // Each AST node has a bunch of getters for children. All getters return
131 // `Option`s though, to account for incomplete code. Some getters are common
132 // for several kinds of node. In this case, a trait like `ast::NameOwner`
133 // usually exists. By convention, all ast types should be used with `ast::`
134 // qualifier.
135 let name: Option<&ast::Name> = func.name();
136 let name = name.unwrap();
137 assert_eq!(name.text(), "foo");
138
139 // Let's get the `1 + 1` expression!
140 let block: &ast::Block = func.body().unwrap();
141 let expr: &ast::Expr = block.expr().unwrap();
142
143 // "Enum"-like nodes are represented using the "kind" pattern. It allows us
144 // to match exhaustively against all flavors of nodes, while maintaining
145 // internal representation flexibility. The drawback is that one can't write
146 // nested matches as one pattern.
147 let bin_expr: &ast::BinExpr = match expr.kind() {
148 ast::ExprKind::BinExpr(e) => e,
149 _ => unreachable!(),
150 };
151
152 // Besides the "typed" AST API, there's an untyped CST one as well.
153 // To switch from AST to CST, call `.syntax()` method:
154 let expr_syntax: &SyntaxNode = expr.syntax();
155
156 // Note how `expr` and `bin_expr` are in fact the same node underneath:
157 assert!(std::ptr::eq(expr_syntax, bin_expr.syntax()));
158
159 // To go from CST to AST, `AstNode::cast` function is used:
160 let expr = match ast::Expr::cast(expr_syntax) {
161 Some(e) => e,
162 None => unreachable!(),
163 };
164
165 // Note how expr is also a reference!
166 let expr: &ast::Expr = expr;
167
168 // This is possible because the underlying representation is the same:
169 assert_eq!(
170 expr as *const ast::Expr as *const u8,
171 expr_syntax as *const SyntaxNode as *const u8
172 );
173
174 // The two properties each syntax node has is a `SyntaxKind`:
175 assert_eq!(expr_syntax.kind(), SyntaxKind::BIN_EXPR);
176
177 // And text range:
178 assert_eq!(expr_syntax.range(), TextRange::from_to(32.into(), 37.into()));
179
180 // You can get node's text as a `SyntaxText` object, which will traverse the
181 // tree collecting token's text:
182 let text: SyntaxText<'_> = expr_syntax.text();
183 assert_eq!(text.to_string(), "1 + 1");
184
185 // There's a bunch of traversal methods on `SyntaxNode`:
186 assert_eq!(expr_syntax.parent(), Some(block.syntax()));
187 assert_eq!(block.syntax().first_child().map(|it| it.kind()), Some(SyntaxKind::L_CURLY));
188 assert_eq!(expr_syntax.next_sibling().map(|it| it.kind()), Some(SyntaxKind::WHITESPACE));
189
190 // As well as some iterator helpers:
191 let f = expr_syntax.ancestors().find_map(ast::FnDef::cast);
192 assert_eq!(f, Some(&*func));
193 assert!(expr_syntax.siblings(Direction::Next).any(|it| it.kind() == SyntaxKind::R_CURLY));
194 assert_eq!(
195 expr_syntax.descendants().count(),
196 8, // 5 tokens `1`, ` `, `+`, ` `, `!`
197 // 2 child literal expressions: `1`, `1`
198 // 1 the node itself: `1 + 1`
199 );
200
201 // There's also a `preorder` method with a more fine-grained iteration control:
202 let mut buf = String::new();
203 let mut indent = 0;
204 for event in expr_syntax.preorder() {
205 match event {
206 WalkEvent::Enter(node) => {
207 buf += &format!(
208 "{:indent$}{:?} {:?}\n",
209 " ",
210 node.text(),
211 node.kind(),
212 indent = indent
213 );
214 indent += 2;
215 }
216 WalkEvent::Leave(_) => indent -= 2,
217 }
218 }
219 assert_eq!(indent, 0);
220 assert_eq!(
221 buf.trim(),
222 r#"
223"1 + 1" BIN_EXPR
224 "1" LITERAL
225 "1" INT_NUMBER
226 " " WHITESPACE
227 "+" PLUS
228 " " WHITESPACE
229 "1" LITERAL
230 "1" INT_NUMBER
231"#
232 .trim()
233 );
234
235 // To recursively process the tree, there are three approaches:
236 // 1. explicitly call getter methods on AST nodes.
237 // 2. use descendants and `AstNode::cast`.
238 // 3. use descendants and the visitor.
239 //
240 // Here's how the first one looks like:
241 let exprs_cast: Vec<String> = file
242 .syntax()
243 .descendants()
244 .filter_map(ast::Expr::cast)
245 .map(|expr| expr.syntax().text().to_string())
246 .collect();
247
248 // An alternative is to use a visitor. The visitor does not do traversal
249 // automatically (so it's more akin to a generic lambda) and is constructed
250 // from closures. This seems more flexible than a single generated visitor
251 // trait.
252 use algo::visit::{visitor, Visitor};
253 let mut exprs_visit = Vec::new();
254 for node in file.syntax().descendants() {
255 if let Some(result) =
256 visitor().visit::<ast::Expr, _>(|expr| expr.syntax().text().to_string()).accept(node)
257 {
258 exprs_visit.push(result);
259 }
260 }
261 assert_eq!(exprs_cast, exprs_visit);
262}