Fix few bugs in closure capture computation, and add tests

Also create a test infrastructure for capture computation.

crates/hir-ty/src/mir.rs

@@ -636,6 +636,7 @@ pub enum TerminatorKind {
     },
 }
 
+// Order of variants in this enum matter: they are used to compare borrow kinds.
 #[derive(Debug, PartialEq, Eq, Clone, Copy, PartialOrd, Ord)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
@@ -666,15 +667,16 @@ pub enum BorrowKind {
     Mut { kind: MutBorrowKind },
 }
 
+// Order of variants in this enum matter: they are used to compare borrow kinds.
 #[derive(Debug, PartialEq, Eq, Clone, Copy, PartialOrd, Ord)]
 pub enum MutBorrowKind {
+    /// Data must be immutable but not aliasable. This kind of borrow cannot currently
+    /// be expressed by the user and is used only in implicit closure bindings.
+    ClosureCapture,
     Default,
     /// This borrow arose from method-call auto-ref
     /// (i.e., adjustment::Adjust::Borrow).
     TwoPhasedBorrow,
-    /// Data must be immutable but not aliasable. This kind of borrow cannot currently
-    /// be expressed by the user and is used only in implicit closure bindings.
-    ClosureCapture,
 }
 
 impl BorrowKind {

crates/hir-ty/src/tests.rs

@@ -1,3 +1,4 @@
+mod closure_captures;
 mod coercion;
 mod diagnostics;
 mod display_source_code;

crates/hir-ty/src/tests/closure_captures.rs

@@ -0,0 +1,284 @@
+use base_db::salsa::InternKey;
+use expect_test::{expect, Expect};
+use hir_def::db::DefDatabase;
+use itertools::Itertools;
+use test_fixture::WithFixture;
+
+use crate::db::{HirDatabase, InternedClosureId};
+use crate::display::HirDisplay;
+use crate::test_db::TestDB;
+
+use super::visit_module;
+
+fn check_closure_captures(ra_fixture: &str, expect: Expect) {
+    let (db, file_id) = TestDB::with_single_file(ra_fixture);
+    let module = db.module_for_file(file_id);
+    let def_map = module.def_map(&db);
+
+    let mut defs = Vec::new();
+    visit_module(&db, &def_map, module.local_id, &mut |it| defs.push(it));
+
+    let mut captures_info = Vec::new();
+    for def in defs {
+        let infer = db.infer(def);
+        let db = &db;
+        captures_info.extend(infer.closure_info.iter().flat_map(|(closure_id, (captures, _))| {
+            let closure = db.lookup_intern_closure(InternedClosureId::from_intern_id(closure_id.0));
+            let (_, source_map) = db.body_with_source_map(closure.0);
+            let closure_text_range = source_map
+                .expr_syntax(closure.1)
+                .expect("failed to map closure to SyntaxNode")
+                .value
+                .text_range();
+            captures.iter().flat_map(move |capture| {
+                // FIXME: Deduplicate this with hir::Local::sources().
+                let (body, source_map) = db.body_with_source_map(closure.0);
+                let local_text_ranges = match body.self_param.zip(source_map.self_param_syntax()) {
+                    Some((param, source)) if param == capture.local() => {
+                        vec![source.file_syntax(db).text_range()]
+                    }
+                    _ => source_map
+                        .patterns_for_binding(capture.local())
+                        .iter()
+                        .map(|&definition| {
+                            let src = source_map.pat_syntax(definition).unwrap();
+                            src.file_syntax(db).text_range()
+                        })
+                        .collect(),
+                };
+                let place = capture.display_place(closure.0, db);
+                let capture_ty = capture.ty.skip_binders().display_test(db).to_string();
+                local_text_ranges.into_iter().map(move |local_text_range| {
+                    (
+                        closure_text_range,
+                        local_text_range,
+                        place.clone(),
+                        capture_ty.clone(),
+                        capture.kind(),
+                    )
+                })
+            })
+        }));
+    }
+    captures_info.sort_unstable_by_key(|(closure_text_range, local_text_range, ..)| {
+        (closure_text_range.start(), local_text_range.start())
+    });
+
+    let rendered = captures_info
+        .iter()
+        .map(|(closure_text_range, local_text_range, place, capture_ty, capture_kind)| {
+            format!(
+                "{closure_text_range:?};{local_text_range:?} {capture_kind:?} {place} {capture_ty}"
+            )
+        })
+        .join("\n");
+
+    expect.assert_eq(&rendered);
+}
+
+#[test]
+fn deref_in_let() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let b = *a; };
+}
+"#,
+        expect!["53..71;0..75 ByRef(Shared) *a &'? bool"],
+    );
+}
+
+#[test]
+fn deref_then_ref_pattern() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let &mut ref b = a; };
+}
+"#,
+        expect!["53..79;0..83 ByRef(Shared) *a &'? bool"],
+    );
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let &mut ref mut b = a; };
+}
+"#,
+        expect!["53..83;0..87 ByRef(Mut { kind: Default }) *a &'? mut bool"],
+    );
+}
+
+#[test]
+fn unique_borrow() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { *a = false; };
+}
+"#,
+        expect!["53..71;0..75 ByRef(Mut { kind: Default }) *a &'? mut bool"],
+    );
+}
+
+#[test]
+fn deref_ref_mut() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let ref mut b = *a; };
+}
+"#,
+        expect!["53..79;0..83 ByRef(Mut { kind: Default }) *a &'? mut bool"],
+    );
+}
+
+#[test]
+fn let_else_not_consuming() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+fn main() {
+    let a = &mut true;
+    let closure = || { let _ = *a else { return; }; };
+}
+"#,
+        expect!["53..88;0..92 ByRef(Shared) *a &'? bool"],
+    );
+}
+
+#[test]
+fn consume() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let a = NonCopy;
+    let closure = || { let b = a; };
+}
+"#,
+        expect!["67..84;0..88 ByValue a NonCopy"],
+    );
+}
+
+#[test]
+fn ref_to_upvar() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let mut a = NonCopy;
+    let closure = || { let b = &a; };
+    let closure = || { let c = &mut a; };
+}
+"#,
+        expect![[r#"
+            71..89;0..135 ByRef(Shared) a &'? NonCopy
+            109..131;0..135 ByRef(Mut { kind: Default }) a &'? mut NonCopy"#]],
+    );
+}
+
+#[test]
+fn field() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct Foo { a: i32, b: i32 }
+fn main() {
+    let a = Foo { a: 0, b: 0 };
+    let closure = || { let b = a.a; };
+}
+"#,
+        expect!["92..111;0..115 ByRef(Shared) a.a &'? i32"],
+    );
+}
+
+#[test]
+fn fields_different_mode() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+struct Foo { a: i32, b: i32, c: NonCopy, d: bool }
+fn main() {
+    let mut a = Foo { a: 0, b: 0 };
+    let closure = || {
+        let b = &a.a;
+        let c = &mut a.b;
+        let d = a.c;
+    };
+}
+"#,
+        expect![[r#"
+            133..212;0..216 ByRef(Shared) a.a &'? i32
+            133..212;0..216 ByRef(Mut { kind: Default }) a.b &'? mut i32
+            133..212;0..216 ByValue a.c NonCopy"#]],
+    );
+}
+
+#[test]
+fn autoref() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct Foo;
+impl Foo {
+    fn imm(&self) {}
+    fn mut_(&mut self) {}
+}
+fn main() {
+    let mut a = Foo;
+    let closure = || a.imm();
+    let closure = || a.mut_();
+}
+"#,
+        expect![[r#"
+            123..133;0..168 ByRef(Shared) a &'? Foo
+            153..164;0..168 ByRef(Mut { kind: Default }) a &'? mut Foo"#]],
+    );
+}
+
+#[test]
+fn captures_priority() {
+    check_closure_captures(
+        r#"
+//- minicore:copy
+struct NonCopy;
+fn main() {
+    let mut a = &mut true;
+    // Max ByRef(Mut { kind: Default })
+    let closure = || {
+        *a = false;
+        let b = &mut a;
+    };
+    // Max ByRef(Mut { kind: ClosureCapture })
+    let closure = || {
+        let b = *a;
+        let c = &mut *a;
+    };
+    // Max ByValue
+    let mut a = NonCopy;
+    let closure = || {
+        let b = a;
+        let c = &mut a;
+        let d = &a;
+    };
+}
+"#,
+        expect![[r#"
+            113..167;0..430 ByRef(Mut { kind: Default }) a &'? mut &'? mut bool
+            234..289;0..430 ByRef(Mut { kind: Default }) *a &'? mut bool
+            353..426;0..430 ByValue a NonCopy"#]],
+    );
+}

crates/hir/src/lib.rs

@@ -4133,6 +4133,7 @@ impl ClosureCapture {
     }
 }
 
+#[derive(Clone, Copy, PartialEq, Eq)]
 pub enum CaptureKind {
     SharedRef,
     UniqueSharedRef,