Match some known simple containers

NEWS.md

@@ -1,5 +1,10 @@
 # cargo-mutants changelog
 
+## Unreleased
+
+- Mutate `BinaryHeap`, `BTreeSet`, `HashSet`, `LinkedList`, and `VecDeque` to
+  generate empty and one-element containers.
+
 ## 23.6.0
 
 - Generate `Box::leak(Box::new(...))` as a mutation of functions returning

book/src/mutants.md

@@ -31,6 +31,7 @@ More mutation genres and patterns will be added in future releases.
 | `Vec<T>`          | `vec![]`, `vec![...]`                                      |
 | `Arc<T>`          | `Arc::new(...)`                                            |
 | `Rc<T>`           | `Rc::new(...)`                                             |
+| `BinaryHeap`, `BTreeSet`, `HashSet`, `LinkedList`, `VecDeque` | empty and one-element collections |
 | `[T; L]`          | `[r; L]` for all replacements of T                         |
 | `&T`              | `&...` (all replacements for T)                            |
 | (any other)       | `Default::default()`                                       |

src/visit.rs

@@ -385,7 +385,7 @@ fn type_replacements(type_: &Type, error_exprs: &[Expr]) -> Vec<TokenStream> {
                             quote! { vec![#rep] }
                         }),
                 )
-            } else if let Some((container_type, inner_type)) = known_simple_container(path) {
+            } else if let Some((container_type, inner_type)) = known_container(path) {
                 // Something like Arc, Mutex, etc.
 
                 // TODO: Ideally we should use the path without relying on it being
@@ -399,6 +399,15 @@ fn type_replacements(type_: &Type, error_exprs: &[Expr]) -> Vec<TokenStream> {
                             quote! { #container_type::new(#rep) }
                         }),
                 )
+            } else if let Some((collection_type, inner_type)) = known_collection(path) {
+                reps.push(quote! { #collection_type::new() });
+                reps.extend(
+                    type_replacements(inner_type, error_exprs)
+                        .into_iter()
+                        .map(|rep| {
+                            quote! { #collection_type::from_iter([#rep]) }
+                        }),
+                );
             } else {
                 reps.push(quote! { Default::default() });
             }
@@ -475,7 +484,7 @@ fn path_ends_with(path: &Path, ident: &str) -> bool {
 /// like Box, Cell, Mutex, etc, that can be constructed with `T::new(inner_val)`.
 ///
 /// If so, return the short name (like "Box") and the inner type.
-fn known_simple_container(path: &Path) -> Option<(&Ident, &Type)> {
+fn known_container(path: &Path) -> Option<(&Ident, &Type)> {
     let last = path.segments.last()?;
     if !["Box", "Cell", "RefCell", "Arc", "Rc", "Mutex"]
         .iter()
@@ -497,6 +506,36 @@ fn known_simple_container(path: &Path) -> Option<(&Ident, &Type)> {
     None
 }
 
+/// Match known simple collections that can be empty or constructed from an
+/// iterator.
+fn known_collection(path: &Path) -> Option<(&Ident, &Type)> {
+    let last = path.segments.last()?;
+    if ![
+        "BinaryHeap",
+        "BTreeSet",
+        "HashSet",
+        "LinkedList",
+        "VecDeque",
+    ]
+    .iter()
+    .any(|v| last.ident == v)
+    {
+        return None;
+    }
+    if let PathArguments::AngleBracketed(AngleBracketedGenericArguments { args, .. }) =
+        &last.arguments
+    {
+        // TODO: Skip lifetime args.
+        // TODO: Return the path with args stripped out.
+        if args.len() == 1 {
+            if let Some(GenericArgument::Type(inner_type)) = args.first() {
+                return Some((&last.ident, inner_type));
+            }
+        }
+    }
+    None
+}
+
 fn path_is_float(path: &Path) -> bool {
     ["f32", "f64"].iter().any(|s| path.is_ident(s))
 }
@@ -908,6 +947,18 @@ mod test {
         );
     }
 
+    #[test]
+    fn btreeset_replacement() {
+        assert_eq!(
+            replace(&parse_quote! { -> std::collections::BTreeSet<String> }, &[]),
+            &[
+                "BTreeSet::new()",
+                "BTreeSet::from_iter([String::new()])",
+                "BTreeSet::from_iter([\"xyzzy\".into()])"
+            ]
+        );
+    }
+
     fn replace(return_type: &ReturnType, error_exprs: &[Expr]) -> Vec<String> {
         return_type_replacements(return_type, error_exprs)
             .into_iter()

testdata/tree/well_tested/src/lib.rs

@@ -16,5 +16,6 @@ mod methods;
 mod nested_function;
 mod numbers;
 mod result;
+mod sets;
 pub mod simple_fns;
 mod struct_with_lifetime;

testdata/tree/well_tested/src/sets.rs

@@ -0,0 +1,13 @@
+use std::collections::BTreeSet;
+
+fn make_a_set() -> BTreeSet<String> {
+    let mut s = BTreeSet::new();
+    s.insert("one".into());
+    s.insert("two".into());
+    s
+}
+
+#[test]
+fn set_has_two_elements() {
+    assert_eq!(make_a_set().len(), 2);
+}

tests/cli/main.rs

@@ -622,8 +622,8 @@ fn well_tested_tree_quiet() {
         fs::read_to_string(tmp_src_dir.path().join("mutants.out/outcomes.json")).unwrap();
     println!("outcomes.json:\n{outcomes_json}");
     let outcomes: serde_json::Value = outcomes_json.parse().unwrap();
-    assert_eq!(outcomes["total_mutants"], 27);
-    assert_eq!(outcomes["caught"], 27);
+    assert_eq!(outcomes["total_mutants"], 30);
+    assert_eq!(outcomes["caught"], 30);
     assert_eq!(outcomes["unviable"], 0);
     assert_eq!(outcomes["missed"], 0);
 }

tests/cli/snapshots/cli__list_files_json_well_tested.snap

@@ -1,5 +1,6 @@
 ---
 source: tests/cli/main.rs
+assertion_line: 73
 expression: "String::from_utf8_lossy(&output.stdout)"
 ---
 [
@@ -39,6 +40,10 @@ expression: "String::from_utf8_lossy(&output.stdout)"
     "package": "cargo-mutants-testdata-well-tested",
     "path": "src/result.rs"
   },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "path": "src/sets.rs"
+  },
   {
     "package": "cargo-mutants-testdata-well-tested",
     "path": "src/simple_fns.rs"

tests/cli/snapshots/cli__list_files_text_well_tested.snap

@@ -1,5 +1,6 @@
 ---
 source: tests/cli/main.rs
+assertion_line: 73
 expression: "String::from_utf8_lossy(&output.stdout)"
 ---
 src/lib.rs
@@ -11,6 +12,7 @@ src/methods.rs
 src/nested_function.rs
 src/numbers.rs
 src/result.rs
+src/sets.rs
 src/simple_fns.rs
 src/struct_with_lifetime.rs
 

tests/cli/snapshots/cli__list_mutants_in_all_trees_as_json.snap

@@ -873,6 +873,33 @@ expression: buf
     "replacement": "Ok(Default::default())",
     "genre": "FnValue"
   },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "file": "src/sets.rs",
+    "line": 3,
+    "function": "make_a_set",
+    "return_type": "-> BTreeSet<String>",
+    "replacement": "BTreeSet::new()",
+    "genre": "FnValue"
+  },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "file": "src/sets.rs",
+    "line": 3,
+    "function": "make_a_set",
+    "return_type": "-> BTreeSet<String>",
+    "replacement": "BTreeSet::from_iter([String::new()])",
+    "genre": "FnValue"
+  },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "file": "src/sets.rs",
+    "line": 3,
+    "function": "make_a_set",
+    "return_type": "-> BTreeSet<String>",
+    "replacement": "BTreeSet::from_iter([\"xyzzy\".into()])",
+    "genre": "FnValue"
+  },
   {
     "package": "cargo-mutants-testdata-well-tested",
     "file": "src/simple_fns.rs",

tests/cli/snapshots/cli__list_mutants_in_all_trees_as_text.snap

@@ -220,6 +220,9 @@ src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("")
 src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("xyzzy")
 src/result.rs:9: replace error_if_negative -> Result<(), ()> with Ok(())
 src/result.rs:17: replace result_with_no_apparent_type_args -> std::fmt::Result with Ok(Default::default())
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::new()
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter([String::new()])
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter(["xyzzy".into()])
 src/simple_fns.rs:7: replace returns_unit with ()
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 0
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 1

tests/cli/snapshots/cli__list_mutants_json_well_tested.snap

@@ -1,5 +1,6 @@
 ---
 source: tests/cli/main.rs
+assertion_line: 73
 expression: "String::from_utf8_lossy(&output.stdout)"
 ---
 [
@@ -165,6 +166,33 @@ expression: "String::from_utf8_lossy(&output.stdout)"
     "replacement": "Ok(Default::default())",
     "genre": "FnValue"
   },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "file": "src/sets.rs",
+    "line": 3,
+    "function": "make_a_set",
+    "return_type": "-> BTreeSet<String>",
+    "replacement": "BTreeSet::new()",
+    "genre": "FnValue"
+  },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "file": "src/sets.rs",
+    "line": 3,
+    "function": "make_a_set",
+    "return_type": "-> BTreeSet<String>",
+    "replacement": "BTreeSet::from_iter([String::new()])",
+    "genre": "FnValue"
+  },
+  {
+    "package": "cargo-mutants-testdata-well-tested",
+    "file": "src/sets.rs",
+    "line": 3,
+    "function": "make_a_set",
+    "return_type": "-> BTreeSet<String>",
+    "replacement": "BTreeSet::from_iter([\"xyzzy\".into()])",
+    "genre": "FnValue"
+  },
   {
     "package": "cargo-mutants-testdata-well-tested",
     "file": "src/simple_fns.rs",

tests/cli/snapshots/cli__list_mutants_well_tested.snap

@@ -1,5 +1,6 @@
 ---
 source: tests/cli/main.rs
+assertion_line: 73
 expression: "String::from_utf8_lossy(&output.stdout)"
 ---
 src/arc.rs:3: replace return_arc -> Arc<String> with Arc::new(String::new())
@@ -20,6 +21,9 @@ src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("")
 src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("xyzzy")
 src/result.rs:9: replace error_if_negative -> Result<(), ()> with Ok(())
 src/result.rs:17: replace result_with_no_apparent_type_args -> std::fmt::Result with Ok(Default::default())
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::new()
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter([String::new()])
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter(["xyzzy".into()])
 src/simple_fns.rs:7: replace returns_unit with ()
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 0
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 1

tests/cli/snapshots/cli__list_mutants_well_tested_exclude_name_filter.snap

@@ -20,6 +20,9 @@ src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("")
 src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("xyzzy")
 src/result.rs:9: replace error_if_negative -> Result<(), ()> with Ok(())
 src/result.rs:17: replace result_with_no_apparent_type_args -> std::fmt::Result with Ok(Default::default())
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::new()
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter([String::new()])
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter(["xyzzy".into()])
 src/struct_with_lifetime.rs:14: replace Lex<'buf>::buf_len -> usize with 0
 src/struct_with_lifetime.rs:14: replace Lex<'buf>::buf_len -> usize with 1
 

tests/cli/snapshots/cli__well_tested_tree_check_only.snap

@@ -2,7 +2,7 @@
 source: tests/cli/main.rs
 expression: stdout
 ---
-Found 27 mutants to test
+Found 30 mutants to test
 Unmutated baseline ... ok
 src/arc.rs:3: replace return_arc -> Arc<String> with Arc::new(String::new()) ... ok
 src/arc.rs:3: replace return_arc -> Arc<String> with Arc::new("xyzzy".into()) ... ok
@@ -22,6 +22,9 @@ src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("") .
 src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("xyzzy") ... ok
 src/result.rs:9: replace error_if_negative -> Result<(), ()> with Ok(()) ... ok
 src/result.rs:17: replace result_with_no_apparent_type_args -> std::fmt::Result with Ok(Default::default()) ... ok
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::new() ... ok
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter([String::new()]) ... ok
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter(["xyzzy".into()]) ... ok
 src/simple_fns.rs:7: replace returns_unit with () ... ok
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 0 ... ok
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 1 ... ok
@@ -31,5 +34,5 @@ src/simple_fns.rs:26: replace double_string -> String with String::new() ... ok
 src/simple_fns.rs:26: replace double_string -> String with "xyzzy".into() ... ok
 src/struct_with_lifetime.rs:14: replace Lex<'buf>::buf_len -> usize with 0 ... ok
 src/struct_with_lifetime.rs:14: replace Lex<'buf>::buf_len -> usize with 1 ... ok
-27 mutants tested: 27 succeeded
+30 mutants tested: 30 succeeded
 

tests/cli/snapshots/cli__well_tested_tree_finds_no_problems.snap

@@ -2,7 +2,7 @@
 source: tests/cli/main.rs
 expression: stdout
 ---
-Found 27 mutants to test
+Found 30 mutants to test
 Unmutated baseline ... ok
 src/arc.rs:3: replace return_arc -> Arc<String> with Arc::new(String::new()) ... caught
 src/arc.rs:3: replace return_arc -> Arc<String> with Arc::new("xyzzy".into()) ... caught
@@ -22,6 +22,9 @@ src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("") .
 src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("xyzzy") ... caught
 src/result.rs:9: replace error_if_negative -> Result<(), ()> with Ok(()) ... caught
 src/result.rs:17: replace result_with_no_apparent_type_args -> std::fmt::Result with Ok(Default::default()) ... caught
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::new() ... caught
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter([String::new()]) ... caught
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter(["xyzzy".into()]) ... caught
 src/simple_fns.rs:7: replace returns_unit with () ... caught
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 0 ... caught
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 1 ... caught
@@ -31,5 +34,5 @@ src/simple_fns.rs:26: replace double_string -> String with String::new() ... cau
 src/simple_fns.rs:26: replace double_string -> String with "xyzzy".into() ... caught
 src/struct_with_lifetime.rs:14: replace Lex<'buf>::buf_len -> usize with 0 ... caught
 src/struct_with_lifetime.rs:14: replace Lex<'buf>::buf_len -> usize with 1 ... caught
-27 mutants tested: 27 caught
+30 mutants tested: 30 caught
 

tests/cli/snapshots/cli__well_tested_tree_finds_no_problems__caught.txt.snap

@@ -20,6 +20,9 @@ src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("")
 src/result.rs:5: replace simple_result -> Result<&'static str, ()> with Ok("xyzzy")
 src/result.rs:9: replace error_if_negative -> Result<(), ()> with Ok(())
 src/result.rs:17: replace result_with_no_apparent_type_args -> std::fmt::Result with Ok(Default::default())
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::new()
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter([String::new()])
+src/sets.rs:3: replace make_a_set -> BTreeSet<String> with BTreeSet::from_iter(["xyzzy".into()])
 src/simple_fns.rs:7: replace returns_unit with ()
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 0
 src/simple_fns.rs:12: replace returns_42u32 -> u32 with 1

tests/cli/snapshots/cli__well_tested_tree_quiet.snap

@@ -2,7 +2,7 @@
 source: tests/cli/main.rs
 expression: stdout
 ---
-Found 27 mutants to test
+Found 30 mutants to test
 Unmutated baseline ... ok
-27 mutants tested: 27 caught
+30 mutants tested: 30 caught