1 files changed, 75 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/syntax/src/fuzz.rs b/src/tools/rust-analyzer/crates/syntax/src/fuzz.rs
new file mode 100644
index 000000000..256999fe0
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/syntax/src/fuzz.rs
@@ -0,0 +1,75 @@
+//! Some infrastructure for fuzzy testing.
+//!
+//! We don't normally run fuzzying, so this is hopelessly bitrotten :(
+
+use std::{
+    convert::TryInto,
+    str::{self, FromStr},
+};
+
+use text_edit::Indel;
+
+use crate::{validation, AstNode, SourceFile, TextRange};
+
+fn check_file_invariants(file: &SourceFile) {
+    let root = file.syntax();
+    validation::validate_block_structure(root);
+}
+
+pub fn check_parser(text: &str) {
+    let file = SourceFile::parse(text);
+    check_file_invariants(&file.tree());
+}
+
+#[derive(Debug, Clone)]
+pub struct CheckReparse {
+    text: String,
+    edit: Indel,
+    edited_text: String,
+}
+
+impl CheckReparse {
+    pub fn from_data(data: &[u8]) -> Option<Self> {
+        const PREFIX: &str = "fn main(){\n\t";
+        const SUFFIX: &str = "\n}";
+
+        let data = str::from_utf8(data).ok()?;
+        let mut lines = data.lines();
+        let delete_start = usize::from_str(lines.next()?).ok()? + PREFIX.len();
+        let delete_len = usize::from_str(lines.next()?).ok()?;
+        let insert = lines.next()?.to_string();
+        let text = lines.collect::<Vec<_>>().join("\n");
+        let text = format!("{}{}{}", PREFIX, text, SUFFIX);
+        text.get(delete_start..delete_start.checked_add(delete_len)?)?; // make sure delete is a valid range
+        let delete =
+            TextRange::at(delete_start.try_into().unwrap(), delete_len.try_into().unwrap());
+        let edited_text =
+            format!("{}{}{}", &text[..delete_start], &insert, &text[delete_start + delete_len..]);
+        let edit = Indel { insert, delete };
+        Some(CheckReparse { text, edit, edited_text })
+    }
+
+    pub fn run(&self) {
+        let parse = SourceFile::parse(&self.text);
+        let new_parse = parse.reparse(&self.edit);
+        check_file_invariants(&new_parse.tree());
+        assert_eq!(&new_parse.tree().syntax().text().to_string(), &self.edited_text);
+        let full_reparse = SourceFile::parse(&self.edited_text);
+        for (a, b) in
+            new_parse.tree().syntax().descendants().zip(full_reparse.tree().syntax().descendants())
+        {
+            if (a.kind(), a.text_range()) != (b.kind(), b.text_range()) {
+                eprint!("original:\n{:#?}", parse.tree().syntax());
+                eprint!("reparsed:\n{:#?}", new_parse.tree().syntax());
+                eprint!("full reparse:\n{:#?}", full_reparse.tree().syntax());
+                assert_eq!(
+                    format!("{:?}", a),
+                    format!("{:?}", b),
+                    "different syntax tree produced by the full reparse"
+                );
+            }
+        }
+        // FIXME
+        // assert_eq!(new_file.errors(), full_reparse.errors());
+    }
+}