proptest strategies for TextUnit and AtomTextEdit

2 files changed, 116 insertions, 0 deletions

diff --git a/crates/ra_text_edit/src/lib.rs b/crates/ra_text_edit/src/lib.rs
index 13e20f6fb..0a407795e 100644
--- a/crates/ra_text_edit/src/lib.rs
+++ b/crates/ra_text_edit/src/lib.rs
@@ -1,5 +1,7 @@
 mod text_edit;
 pub mod text_utils;
+#[cfg(test)]
+pub mod test_utils;
 
 pub use crate::text_edit::{TextEdit, TextEditBuilder};
 
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..92b79ab59
--- /dev/null
+++ b/crates/ra_text_edit/src/test_utils.rs
@@ -0,0 +1,114 @@
+use proptest::{prelude::*, proptest, proptest_helper};
+use text_unit::{TextUnit, TextRange};
+use crate::AtomTextEdit;
+
+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_edits(text: &str) -> BoxedStrategy<Vec<AtomTextEdit>> {
+    let offsets = text_offsets(text);
+    let offsets_len = offsets.len();
+
+    if offsets_len == 0 {
+        return proptest::bool::ANY
+            .prop_flat_map(|b| {
+                // only valid edits
+                if b {
+                    arb_text()
+                        .prop_map(|text| vec![AtomTextEdit::insert(TextUnit::from(0), text)])
+                        .boxed()
+                } else {
+                    Just(vec![]).boxed()
+                }
+            })
+            .boxed();
+    }
+
+    proptest::sample::subsequence(offsets, 0..offsets_len)
+        .prop_flat_map(|xs| {
+            let strategies: Vec<_> = xs
+                .chunks(2)
+                .map(|chunk| match chunk {
+                    &[from, to] => {
+                        let range = TextRange::from_to(from, to);
+                        (proptest::bool::ANY)
+                            .prop_flat_map(move |b| {
+                                if b {
+                                    Just(AtomTextEdit::delete(range)).boxed()
+                                } else {
+                                    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
+        })
+        .boxed()
+}
+
+fn arb_text_with_edits() -> BoxedStrategy<(String, Vec<AtomTextEdit>)> {
+    let text = arb_text();
+    text.prop_flat_map(|s| {
+        let edits = arb_edits(&s);
+        (Just(s), edits)
+    })
+    .boxed()
+}
+
+fn intersect(r1: TextRange, r2: TextRange) -> Option<TextRange> {
+    let start = r1.start().max(r2.start());
+    let end = r1.end().min(r2.end());
+    if start <= end {
+        Some(TextRange::from_to(start, end))
+    } else {
+        None
+    }
+}
+
+proptest! {
+#[test]
+    fn atom_text_edits_are_valid((text, edits) in arb_text_with_edits()) {
+        proptest_atom_text_edits_are_valid(text, edits)
+    }
+}
+
+fn proptest_atom_text_edits_are_valid(text: String, edits: Vec<AtomTextEdit>) {
+    // slicing doesn't panic
+    for e in &edits {
+        let _ = &text[e.delete];
+    }
+    // ranges do not overlap
+    for (i1, e1) in edits.iter().skip(1).enumerate() {
+        for e2 in &edits[0..i1] {
+            if intersect(e1.delete, e2.delete).is_some() {
+                assert!(false, "Overlapping ranges {} {}", e1.delete, e2.delete);
+            }
+        }
+    }
+}