1 files changed, 85 insertions, 0 deletions

diff --git a/crates/ra_text_edit/src/test_utils.rs b/crates/ra_text_edit/src/test_utils.rs
new file mode 100644
index 000000000..745f21c93
--- /dev/null
+++ b/crates/ra_text_edit/src/test_utils.rs
@@ -0,0 +1,85 @@
+use proptest::prelude::*;
+use text_unit::{TextUnit, TextRange};
+use crate::{AtomTextEdit, TextEdit};
+
+pub fn arb_text() -> proptest::string::RegexGeneratorStrategy<String> {
+    // generate multiple newlines
+    proptest::string::string_regex("(.*\n?)*").unwrap()
+}
+
+fn text_offsets(text: &str) -> Vec<TextUnit> {
+    text.char_indices()
+        .map(|(i, _)| TextUnit::from_usize(i))
+        .collect()
+}
+
+pub fn arb_offset(text: &str) -> BoxedStrategy<TextUnit> {
+    let offsets = text_offsets(text);
+    // this is necessary to avoid "Uniform::new called with `low >= high`" panic
+    if offsets.is_empty() {
+        Just(TextUnit::from(0)).boxed()
+    } else {
+        prop::sample::select(offsets).boxed()
+    }
+}
+
+pub fn arb_text_edit(text: &str) -> BoxedStrategy<TextEdit> {
+    if text.is_empty() {
+        // only valid edits
+        return Just(vec![])
+            .boxed()
+            .prop_union(
+                arb_text()
+                    .prop_map(|text| vec![AtomTextEdit::insert(TextUnit::from(0), text)])
+                    .boxed(),
+            )
+            .prop_map(TextEdit::from_atoms)
+            .boxed();
+    }
+
+    let offsets = text_offsets(text);
+    let max_cuts = 7.min(offsets.len());
+
+    proptest::sample::subsequence(offsets, 0..max_cuts)
+        .prop_flat_map(|cuts| {
+            let strategies: Vec<_> = cuts
+                .chunks(2)
+                .map(|chunk| match chunk {
+                    &[from, to] => {
+                        let range = TextRange::from_to(from, to);
+                        Just(AtomTextEdit::delete(range))
+                            .boxed()
+                            .prop_union(
+                                arb_text()
+                                    .prop_map(move |text| AtomTextEdit::replace(range, text))
+                                    .boxed(),
+                            )
+                            .boxed()
+                    }
+                    &[x] => arb_text()
+                        .prop_map(move |text| AtomTextEdit::insert(x, text))
+                        .boxed(),
+                    _ => unreachable!(),
+                })
+                .collect();
+            strategies
+        })
+        .prop_map(TextEdit::from_atoms)
+        .boxed()
+}
+
+#[derive(Debug, Clone)]
+pub struct ArbTextWithEdit {
+    pub text: String,
+    pub edit: TextEdit,
+}
+
+pub fn arb_text_with_edit() -> BoxedStrategy<ArbTextWithEdit> {
+    let text = arb_text();
+    text.prop_flat_map(|s| {
+        let edit = arb_text_edit(&s);
+        (Just(s), edit)
+    })
+    .prop_map(|(text, edit)| ArbTextWithEdit { text, edit })
+    .boxed()
+}