Merge #701

701: Minor type inference tweaks r=flodiebold a=marcusklaas

Pass down expectation for reference expressions and type the guard in match expressions.

I wasn't able to add a test for the former addition because the type variable previously introduced would always resolve to the right type in the things I tried!

Co-authored-by: Marcus Klaas de Vries <mail@marcusklaas.nl>

crates/ra_hir/src/expr.rs

@@ -219,7 +219,7 @@ pub use ra_syntax::ast::BinOp as BinaryOp;
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct MatchArm {
     pub pats: Vec<PatId>,
-    // guard: Option<ExprId>, // TODO
+    pub guard: Option<ExprId>,
     pub expr: ExprId,
 }
 
@@ -515,10 +515,12 @@ impl ExprCollector {
                         MatchArm {
                             pats: vec![pat],
                             expr: then_branch,
+                            guard: None,
                         },
                         MatchArm {
                             pats: vec![placeholder_pat],
                             expr: else_branch,
+                            guard: None,
                         },
                     ];
                     self.alloc_expr(
@@ -617,6 +619,10 @@ impl ExprCollector {
                         .map(|arm| MatchArm {
                             pats: arm.pats().map(|p| self.collect_pat(p)).collect(),
                             expr: self.collect_expr_opt(arm.expr()),
+                            guard: arm
+                                .guard()
+                                .and_then(|guard| guard.expr())
+                                .map(|e| self.collect_expr(e)),
                         })
                         .collect()
                 } else {

crates/ra_hir/src/ty.rs

@@ -1488,7 +1488,9 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     for &pat in &arm.pats {
                         let _pat_ty = self.infer_pat(pat, &input_ty);
                     }
-                    // TODO type the guard
+                    if let Some(guard_expr) = arm.guard {
+                        self.infer_expr(guard_expr, &Expectation::has_type(Ty::Bool));
+                    }
                     self.infer_expr(arm.expr, &expected);
                 }
 
@@ -1561,9 +1563,17 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 cast_ty
             }
             Expr::Ref { expr, mutability } => {
-                // TODO pass the expectation down
+                let expectation = if let Ty::Ref(ref subty, expected_mutability) = expected.ty {
-                let inner_ty = self.infer_expr(*expr, &Expectation::none());
+                    if expected_mutability == Mutability::Mut && *mutability == Mutability::Shared {
+                        // TODO: throw type error - expected mut reference but found shared ref,
+                        // which cannot be coerced
+                    }
+                    Expectation::has_type((**subty).clone())
+                } else {
+                    Expectation::none()
+                };
                 // TODO reference coercions etc.
+                let inner_ty = self.infer_expr(*expr, &expectation);
                 Ty::Ref(Arc::new(inner_ty), *mutability)
             }
             Expr::UnaryOp { expr, op } => {

crates/ra_hir/src/ty/snapshots/tests__infer_adt_pattern.snap

@@ -1,10 +1,10 @@
 ---
-created: "2019-01-22T14:44:59.880187500+00:00"
+created: "2019-01-28T21:58:55.559331849+00:00"
-creator: insta@0.4.0
+creator: insta@0.5.2
 expression: "&result"
-source: "crates\\ra_hir\\src\\ty\\tests.rs"
+source: crates/ra_hir/src/ty/tests.rs
 ---
-[68; 262) '{     ...  d; }': ()
+[68; 289) '{     ...  d; }': ()
 [78; 79) 'e': E
 [82; 95) 'E::A { x: 3 }': E
 [92; 93) '3': usize
@@ -15,15 +15,18 @@ source: "crates\\ra_hir\\src\\ty\\tests.rs"
 [129; 148) 'E::A {..._var }': E
 [139; 146) 'new_var': usize
 [151; 152) 'e': E
-[159; 218) 'match ...     }': usize
+[159; 245) 'match ...     }': usize
 [165; 166) 'e': E
 [177; 187) 'E::A { x }': E
 [184; 185) 'x': usize
 [191; 192) 'x': usize
 [202; 206) 'E::B': E
-[210; 211) '1': usize
+[210; 213) 'foo': bool
-[229; 248) 'ref d ...{ .. }': &E
+[217; 218) '1': usize
-[237; 248) 'E::A { .. }': E
+[228; 232) 'E::B': E
-[251; 252) 'e': E
+[236; 238) '10': usize
-[258; 259) 'd': &E
+[256; 275) 'ref d ...{ .. }': &E
+[264; 275) 'E::A { .. }': E
+[278; 279) 'e': E
+[285; 286) 'd': &E
 

crates/ra_hir/src/ty/snapshots/tests__infer_array.snap

@@ -1,12 +1,12 @@
 ---
-created: "2019-01-22T14:44:59.880187500+00:00"
+created: "2019-01-30T20:08:05.185312835+00:00"
-creator: insta@0.4.0
+creator: insta@0.5.2
 expression: "&result"
-source: "crates\\ra_hir\\src\\ty\\tests.rs"
+source: crates/ra_hir/src/ty/tests.rs
 ---
 [9; 10) 'x': &str
 [18; 19) 'y': isize
-[28; 293) '{     ... []; }': ()
+[28; 324) '{     ... 3]; }': ()
 [38; 39) 'a': [&str]
 [42; 45) '[x]': [&str]
 [43; 44) 'x': &str
@@ -56,4 +56,10 @@ source: "crates\\ra_hir\\src\\ty\\tests.rs"
 [260; 263) '"b"': &str
 [275; 276) 'x': [u8]
 [288; 290) '[]': [u8]
+[300; 301) 'z': &[u8]
+[311; 321) '&[1, 2, 3]': &[u8]
+[312; 321) '[1, 2, 3]': [u8]
+[313; 314) '1': u8
+[316; 317) '2': u8
+[319; 320) '3': u8
 

crates/ra_hir/src/ty/tests.rs

@@ -371,6 +371,7 @@ fn test(x: &str, y: isize) {
 
     let b = [a, ["b"]];
     let x: [u8; 0] = [];
+    let z: &[u8] = &[1, 2, 3];
 }
 "#,
     );
@@ -426,7 +427,8 @@ fn test() {
 
     match e {
         E::A { x } => x,
-        E::B => 1,
+        E::B if foo => 1,
+        E::B => 10,
     };
 
     let ref d @ E::A { .. } = e;

crates/ra_syntax/src/ast/generated.rs

@@ -1981,7 +1981,11 @@ impl ToOwned for MatchGuard {
 }
 
 
-impl MatchGuard {}
+impl MatchGuard {
+    pub fn expr(&self) -> Option<&Expr> {
+        super::child_opt(self)
+    }
+}
 
 // MethodCallExpr
 #[derive(Debug, PartialEq, Eq, Hash)]

crates/ra_syntax/src/grammar.ron

@@ -418,7 +418,7 @@ Grammar(
             ],
             collections: [ [ "pats", "Pat" ] ]
         ),
-        "MatchGuard": (),
+        "MatchGuard": (options: ["Expr"]),
         "StructLit": (options: ["Path", "NamedFieldList", ["spread", "Expr"]]),
         "NamedFieldList": (collections: [ ["fields", "NamedField"] ]),
         "NamedField": (options: ["NameRef", "Expr"]),

crates/ra_syntax/src/grammar/expressions/atom.rs

@@ -360,8 +360,8 @@ fn match_arm(p: &mut Parser) -> BlockLike {
     while p.eat(PIPE) {
         patterns::pattern(p);
     }
-    if p.eat(IF_KW) {
+    if p.at(IF_KW) {
-        expr(p);
+        match_guard(p);
     }
     p.expect(FAT_ARROW);
     let ret = expr_stmt(p);
@@ -369,6 +369,20 @@ fn match_arm(p: &mut Parser) -> BlockLike {
     ret
 }
 
+// test match_guard
+// fn foo() {
+//     match () {
+//         _ if foo => (),
+//     }
+// }
+fn match_guard(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(IF_KW));
+    let m = p.start();
+    p.bump();
+    expr(p);
+    m.complete(p, MATCH_GUARD)
+}
+
 // test block_expr
 // fn foo() {
 //     {};

crates/ra_syntax/tests/data/parser/inline/ok/0066_match_arm.txt

@@ -37,6 +37,7 @@ SOURCE_FILE@[0; 167)
               PLACEHOLDER_PAT@[51; 52)
                 UNDERSCORE@[51; 52)
               WHITESPACE@[52; 53)
+              MATCH_GUARD@[53; 77)
                 IF_KW@[53; 55)
                 WHITESPACE@[55; 56)
                 BIN_EXPR@[56; 77)
@@ -82,6 +83,7 @@ SOURCE_FILE@[0; 167)
                 NAME@[97; 98)
                   IDENT@[97; 98) "Y"
               WHITESPACE@[98; 99)
+              MATCH_GUARD@[99; 103)
                 IF_KW@[99; 101)
                 WHITESPACE@[101; 102)
                 PATH_EXPR@[102; 103)
@@ -110,6 +112,7 @@ SOURCE_FILE@[0; 167)
                 NAME@[125; 126)
                   IDENT@[125; 126) "Y"
               WHITESPACE@[126; 127)
+              MATCH_GUARD@[127; 131)
                 IF_KW@[127; 129)
                 WHITESPACE@[129; 130)
                 PATH_EXPR@[130; 131)

crates/ra_syntax/tests/data/parser/inline/ok/0118_match_guard.rs

@@ -0,0 +1,5 @@
+fn foo() {
+    match () {
+        _ if foo => (),
+    }
+}

crates/ra_syntax/tests/data/parser/inline/ok/0118_match_guard.txt

@@ -0,0 +1,47 @@
+SOURCE_FILE@[0; 58)
+  FN_DEF@[0; 57)
+    FN_KW@[0; 2)
+    WHITESPACE@[2; 3)
+    NAME@[3; 6)
+      IDENT@[3; 6) "foo"
+    PARAM_LIST@[6; 8)
+      L_PAREN@[6; 7)
+      R_PAREN@[7; 8)
+    WHITESPACE@[8; 9)
+    BLOCK@[9; 57)
+      L_CURLY@[9; 10)
+      WHITESPACE@[10; 15)
+      MATCH_EXPR@[15; 55)
+        MATCH_KW@[15; 20)
+        WHITESPACE@[20; 21)
+        TUPLE_EXPR@[21; 23)
+          L_PAREN@[21; 22)
+          R_PAREN@[22; 23)
+        WHITESPACE@[23; 24)
+        MATCH_ARM_LIST@[24; 55)
+          L_CURLY@[24; 25)
+          WHITESPACE@[25; 34)
+          MATCH_ARM@[34; 48)
+            PLACEHOLDER_PAT@[34; 35)
+              UNDERSCORE@[34; 35)
+            WHITESPACE@[35; 36)
+            MATCH_GUARD@[36; 42)
+              IF_KW@[36; 38)
+              WHITESPACE@[38; 39)
+              PATH_EXPR@[39; 42)
+                PATH@[39; 42)
+                  PATH_SEGMENT@[39; 42)
+                    NAME_REF@[39; 42)
+                      IDENT@[39; 42) "foo"
+            WHITESPACE@[42; 43)
+            FAT_ARROW@[43; 45)
+            WHITESPACE@[45; 46)
+            TUPLE_EXPR@[46; 48)
+              L_PAREN@[46; 47)
+              R_PAREN@[47; 48)
+          COMMA@[48; 49)
+          WHITESPACE@[49; 54)
+          R_CURLY@[54; 55)
+      WHITESPACE@[55; 56)
+      R_CURLY@[56; 57)
+  WHITESPACE@[57; 58)