Auto merge of #59288 - Centril:hir-if-to-match, r=oli-obk

[let_chains, 1/6] Remove hir::ExprKind::If

Per https://github.com/rust-lang/rust/issues/53667#issuecomment-471583239.

r? @oli-obk

17 files changed, 287 insertions, 40 deletions

diff --git a/src/test/incremental/hashes/if_expressions.rs b/src/test/incremental/hashes/if_expressions.rs
index fba7869af42..6bc7d286e3a 100644
--- a/src/test/incremental/hashes/if_expressions.rs
+++ b/src/test/incremental/hashes/if_expressions.rs
@@ -94,7 +94,7 @@ pub fn add_else_branch(x: bool) -> u32 {
 }
 
 #[cfg(not(cfail1))]
-#[rustc_clean(cfg="cfail2", except="HirBody,typeck_tables_of")]
+#[rustc_clean(cfg="cfail2", except="HirBody")]
 #[rustc_clean(cfg="cfail3")]
 pub fn add_else_branch(x: bool) -> u32 {
     let mut ret = 1;
@@ -191,7 +191,7 @@ pub fn add_else_branch_if_let(x: Option<u32>) -> u32 {
 }
 
 #[cfg(not(cfail1))]
-#[rustc_clean(cfg="cfail2", except="HirBody,typeck_tables_of")]
+#[rustc_clean(cfg="cfail2", except="HirBody")]
 #[rustc_clean(cfg="cfail3")]
 pub fn add_else_branch_if_let(x: Option<u32>) -> u32 {
     let mut ret = 1;
diff --git a/src/test/mir-opt/issue-38669.rs b/src/test/mir-opt/issue-38669.rs
index 047e623941b..e8ab690bb46 100644
--- a/src/test/mir-opt/issue-38669.rs
+++ b/src/test/mir-opt/issue-38669.rs
@@ -27,15 +27,17 @@ fn main() {
 //     bb3: {
 //         StorageLive(_4);
 //         _4 = _1;
-//         switchInt(move _4) -> [false: bb5, otherwise: bb4];
+//         FakeRead(ForMatchedPlace, _4);
+//         switchInt(_4) -> [false: bb5, otherwise: bb4];
 //     }
-//     bb4: {
+//     ...
+//     bb7: {
 //         _0 = ();
 //         StorageDead(_4);
 //         StorageDead(_1);
 //         return;
 //     }
-//     bb5: {
+//     bb8: {
 //         _3 = ();
 //         StorageDead(_4);
 //         _1 = const true;
diff --git a/src/test/mir-opt/loop_test.rs b/src/test/mir-opt/loop_test.rs
index 34891ee70b5..e75955b9b24 100644
--- a/src/test/mir-opt/loop_test.rs
+++ b/src/test/mir-opt/loop_test.rs
@@ -22,19 +22,20 @@ fn main() {
 //        resume;
 //    }
 //    ...
-//    bb3: { // Entry into the loop
+//    bb6: { // Entry into the loop
 //        _1 = ();
-//        goto -> bb4;
+//        StorageDead(_2);
+//        goto -> bb7;
 //    }
-//    bb4: { // The loop_block
-//        falseUnwind -> [real: bb5, cleanup: bb1];
+//    bb7: { // The loop_block
+//        falseUnwind -> [real: bb8, cleanup: bb1];
 //    }
-//    bb5: { // The loop body (body_block)
-//        StorageLive(_5);
-//        _5 = const 1i32;
-//        FakeRead(ForLet, _5);
-//        StorageDead(_5);
-//        goto -> bb4;
+//    bb8: { // The loop body (body_block)
+//        StorageLive(_6);
+//        _6 = const 1i32;
+//        FakeRead(ForLet, _6);
+//        StorageDead(_6);
+//        goto -> bb7;
 //    }
 //    ...
 // END rustc.main.SimplifyCfg-qualify-consts.after.mir
diff --git a/src/test/mir-opt/nll/region-subtyping-basic.rs b/src/test/mir-opt/nll/region-subtyping-basic.rs
index bb27461bb1e..622cc999830 100644
--- a/src/test/mir-opt/nll/region-subtyping-basic.rs
+++ b/src/test/mir-opt/nll/region-subtyping-basic.rs
@@ -22,9 +22,9 @@ fn main() {
 
 // END RUST SOURCE
 // START rustc.main.nll.0.mir
-// | '_#2r    | U0 | {bb2[0..=5], bb3[0..=1]}
-// | '_#3r    | U0 | {bb2[1..=5], bb3[0..=1]}
-// | '_#4r    | U0 | {bb2[4..=5], bb3[0..=1]}
+// | '_#2r | U0 | {bb2[0..=8], bb3[0], bb6[0..=1]}
+// | '_#3r | U0 | {bb2[1..=8], bb3[0], bb6[0..=1]}
+// | '_#4r | U0 | {bb2[4..=8], bb3[0], bb6[0..=1]}
 // END rustc.main.nll.0.mir
 // START rustc.main.nll.0.mir
 // let _2: &'_#3r usize;
diff --git a/src/test/mir-opt/simplify_if.rs b/src/test/mir-opt/simplify_if.rs
index f6e6c6baf7a..b2a99a6d446 100644
--- a/src/test/mir-opt/simplify_if.rs
+++ b/src/test/mir-opt/simplify_if.rs
@@ -5,13 +5,15 @@ fn main() {
 }
 
 // END RUST SOURCE
-// START rustc.main.SimplifyBranches-initial.before.mir
+// START rustc.main.SimplifyBranches-after-copy-prop.before.mir
 // bb0: {
-//     switchInt(const false) -> [false: bb3, otherwise: bb2];
+//     ...
+//     switchInt(const false) -> [false: bb3, otherwise: bb1];
 // }
-// END rustc.main.SimplifyBranches-initial.before.mir
-// START rustc.main.SimplifyBranches-initial.after.mir
+// END rustc.main.SimplifyBranches-after-copy-prop.before.mir
+// START rustc.main.SimplifyBranches-after-copy-prop.after.mir
 // bb0: {
+//     ...
 //     goto -> bb3;
 // }
-// END rustc.main.SimplifyBranches-initial.after.mir
+// END rustc.main.SimplifyBranches-after-copy-prop.after.mir
diff --git a/src/test/run-pass/if-ret.stderr b/src/test/run-pass/if-ret.stderr
new file mode 100644
index 00000000000..a64281833e5
--- /dev/null
+++ b/src/test/run-pass/if-ret.stderr
@@ -0,0 +1,8 @@
+warning: unreachable block in `if` expression
+  --> $DIR/if-ret.rs:4:24
+   |
+LL | fn foo() { if (return) { } }
+   |                        ^^^
+   |
+   = note: #[warn(unreachable_code)] on by default
+
diff --git a/src/test/ui/if/if-let-arm-types.rs b/src/test/ui/if/if-let-arm-types.rs
index 819f5dd1cfc..0f8815f0479 100644
--- a/src/test/ui/if/if-let-arm-types.rs
+++ b/src/test/ui/if/if-let-arm-types.rs
@@ -1,11 +1,12 @@
 fn main() {
     if let Some(b) = None {
-        //~^ NOTE if let` arms have incompatible types
+        //~^ NOTE if and else have incompatible types
         ()
+        //~^ NOTE expected because of this
     } else {
         1
     };
-    //~^^ ERROR: `if let` arms have incompatible types
+    //~^^ ERROR: if and else have incompatible types
     //~| NOTE expected (), found integer
     //~| NOTE expected type `()`
 }
diff --git a/src/test/ui/if/if-let-arm-types.stderr b/src/test/ui/if/if-let-arm-types.stderr
index b986973fe91..ff88de20f76 100644
--- a/src/test/ui/if/if-let-arm-types.stderr
+++ b/src/test/ui/if/if-let-arm-types.stderr
@@ -1,14 +1,16 @@
-error[E0308]: `if let` arms have incompatible types
-  --> $DIR/if-let-arm-types.rs:6:9
+error[E0308]: if and else have incompatible types
+  --> $DIR/if-let-arm-types.rs:7:9
    |
 LL | /     if let Some(b) = None {
 LL | |
 LL | |         ()
+   | |         -- expected because of this
+LL | |
 LL | |     } else {
 LL | |         1
    | |         ^ expected (), found integer
 LL | |     };
-   | |_____- `if let` arms have incompatible types
+   | |_____- if and else have incompatible types
    |
    = note: expected type `()`
               found type `{integer}`
diff --git a/src/test/ui/if/if-no-match-bindings.rs b/src/test/ui/if/if-no-match-bindings.rs
new file mode 100644
index 00000000000..581ce18c1d6
--- /dev/null
+++ b/src/test/ui/if/if-no-match-bindings.rs
@@ -0,0 +1,22 @@
+// Checks for `if` expressions with respect to default match bindings.
+// Specifically, we do not accept `if cond { ... }` where `cond: &mut? bool`.
+// Meanwhile, `match cond { true => ..., _ => ... }` does accept that.
+
+// FIXME(@rust-lang/lang-team): consider relaxing this?
+
+fn b_ref<'a>() -> &'a bool { &true }
+fn b_mut_ref<'a>() -> &'a mut bool { &mut true }
+
+fn main() {
+    // This is OK:
+    match b_ref() { true => {}, _ => {} }
+    match b_mut_ref() { true => {}, _ => {} }
+    match &true { true => {}, _ => {} }
+    match &mut true { true => {}, _ => {} }
+
+    // This is NOT:
+    if b_ref() {} //~ ERROR mismatched types [E0308]
+    if b_mut_ref() {} //~ ERROR mismatched types [E0308]
+    if &true {} //~ ERROR mismatched types [E0308]
+    if &mut true {} //~ ERROR mismatched types [E0308]
+}
diff --git a/src/test/ui/if/if-no-match-bindings.stderr b/src/test/ui/if/if-no-match-bindings.stderr
new file mode 100644
index 00000000000..7b0b472121f
--- /dev/null
+++ b/src/test/ui/if/if-no-match-bindings.stderr
@@ -0,0 +1,39 @@
+error[E0308]: mismatched types
+  --> $DIR/if-no-match-bindings.rs:18:8
+   |
+LL |     if b_ref() {}
+   |        ^^^^^^^ expected bool, found &bool
+   |
+   = note: expected type `bool`
+              found type `&bool`
+
+error[E0308]: mismatched types
+  --> $DIR/if-no-match-bindings.rs:19:8
+   |
+LL |     if b_mut_ref() {}
+   |        ^^^^^^^^^^^ expected bool, found &mut bool
+   |
+   = note: expected type `bool`
+              found type `&mut bool`
+
+error[E0308]: mismatched types
+  --> $DIR/if-no-match-bindings.rs:20:8
+   |
+LL |     if &true {}
+   |        ^^^^^ expected bool, found &bool
+   |
+   = note: expected type `bool`
+              found type `&bool`
+
+error[E0308]: mismatched types
+  --> $DIR/if-no-match-bindings.rs:21:8
+   |
+LL |     if &mut true {}
+   |        ^^^^^^^^^ expected bool, found &mut bool
+   |
+   = note: expected type `bool`
+              found type `&mut bool`
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/if/if-without-else-as-fn-expr.rs b/src/test/ui/if/if-without-else-as-fn-expr.rs
index 67e4445629f..15892de8385 100644
--- a/src/test/ui/if/if-without-else-as-fn-expr.rs
+++ b/src/test/ui/if/if-without-else-as-fn-expr.rs
@@ -3,6 +3,7 @@ fn foo(bar: usize) -> usize {
         return 3;
     }
     //~^^^ ERROR if may be missing an else clause
+    //~| ERROR mismatched types [E0308]
 }
 
 fn foo2(bar: usize) -> usize {
@@ -10,6 +11,7 @@ fn foo2(bar: usize) -> usize {
         return 3;
     };
     //~^^^ ERROR if may be missing an else clause
+    //~| ERROR mismatched types [E0308]
     x
 }
 
@@ -18,8 +20,36 @@ fn foo3(bar: usize) -> usize {
         3
     }
     //~^^^ ERROR if may be missing an else clause
+    //~| ERROR mismatched types [E0308]
 }
 
+fn foo_let(bar: usize) -> usize {
+    if let 0 = 1 {
+        return 3;
+    }
+    //~^^^ ERROR if may be missing an else clause
+    //~| ERROR mismatched types [E0308]
+}
+
+fn foo2_let(bar: usize) -> usize {
+    let x: usize = if let 0 = 1 {
+        return 3;
+    };
+    //~^^^ ERROR if may be missing an else clause
+    //~| ERROR mismatched types [E0308]
+    x
+}
+
+fn foo3_let(bar: usize) -> usize {
+    if let 0 = 1 {
+        3
+    }
+    //~^^^ ERROR if may be missing an else clause
+    //~| ERROR mismatched types [E0308]
+}
+
+// FIXME(60254): deduplicate first error in favor of second.
+
 fn main() {
     let _ = foo(1);
 }
diff --git a/src/test/ui/if/if-without-else-as-fn-expr.stderr b/src/test/ui/if/if-without-else-as-fn-expr.stderr
index 0ba72726ca7..06600b1cb9a 100644
--- a/src/test/ui/if/if-without-else-as-fn-expr.stderr
+++ b/src/test/ui/if/if-without-else-as-fn-expr.stderr
@@ -1,3 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/if-without-else-as-fn-expr.rs:2:5
+   |
+LL | /     if bar % 5 == 0 {
+LL | |         return 3;
+LL | |     }
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
 error[E0317]: if may be missing an else clause
   --> $DIR/if-without-else-as-fn-expr.rs:2:5
    |
@@ -13,8 +24,20 @@ LL | |     }
    = note: `if` expressions without `else` evaluate to `()`
    = help: consider adding an `else` block that evaluates to the expected type
 
+error[E0308]: mismatched types
+  --> $DIR/if-without-else-as-fn-expr.rs:10:20
+   |
+LL |       let x: usize = if bar % 5 == 0 {
+   |  ____________________^
+LL | |         return 3;
+LL | |     };
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
 error[E0317]: if may be missing an else clause
-  --> $DIR/if-without-else-as-fn-expr.rs:9:20
+  --> $DIR/if-without-else-as-fn-expr.rs:10:20
    |
 LL |       let x: usize = if bar % 5 == 0 {
    |  _________-__________^
@@ -29,8 +52,19 @@ LL | |     };
    = note: `if` expressions without `else` evaluate to `()`
    = help: consider adding an `else` block that evaluates to the expected type
 
+error[E0308]: mismatched types
+  --> $DIR/if-without-else-as-fn-expr.rs:19:5
+   |
+LL | /     if bar % 5 == 0 {
+LL | |         3
+LL | |     }
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
 error[E0317]: if may be missing an else clause
-  --> $DIR/if-without-else-as-fn-expr.rs:17:5
+  --> $DIR/if-without-else-as-fn-expr.rs:19:5
    |
 LL |   fn foo3(bar: usize) -> usize {
    |                          ----- expected `usize` because of this return type
@@ -44,6 +78,87 @@ LL | |     }
    = note: `if` expressions without `else` evaluate to `()`
    = help: consider adding an `else` block that evaluates to the expected type
 
-error: aborting due to 3 previous errors
+error[E0308]: mismatched types
+  --> $DIR/if-without-else-as-fn-expr.rs:27:5
+   |
+LL | /     if let 0 = 1 {
+LL | |         return 3;
+LL | |     }
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
+error[E0317]: if may be missing an else clause
+  --> $DIR/if-without-else-as-fn-expr.rs:27:5
+   |
+LL |   fn foo_let(bar: usize) -> usize {
+   |                             ----- expected `usize` because of this return type
+LL | /     if let 0 = 1 {
+LL | |         return 3;
+LL | |     }
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+   = note: `if` expressions without `else` evaluate to `()`
+   = help: consider adding an `else` block that evaluates to the expected type
+
+error[E0308]: mismatched types
+  --> $DIR/if-without-else-as-fn-expr.rs:35:20
+   |
+LL |       let x: usize = if let 0 = 1 {
+   |  ____________________^
+LL | |         return 3;
+LL | |     };
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
+error[E0317]: if may be missing an else clause
+  --> $DIR/if-without-else-as-fn-expr.rs:35:20
+   |
+LL |       let x: usize = if let 0 = 1 {
+   |  _________-__________^
+   | |         |
+   | |         expected because of this assignment
+LL | |         return 3;
+LL | |     };
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+   = note: `if` expressions without `else` evaluate to `()`
+   = help: consider adding an `else` block that evaluates to the expected type
+
+error[E0308]: mismatched types
+  --> $DIR/if-without-else-as-fn-expr.rs:44:5
+   |
+LL | /     if let 0 = 1 {
+LL | |         3
+LL | |     }
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+
+error[E0317]: if may be missing an else clause
+  --> $DIR/if-without-else-as-fn-expr.rs:44:5
+   |
+LL |   fn foo3_let(bar: usize) -> usize {
+   |                              ----- expected `usize` because of this return type
+LL | /     if let 0 = 1 {
+LL | |         3
+LL | |     }
+   | |_____^ expected usize, found ()
+   |
+   = note: expected type `usize`
+              found type `()`
+   = note: `if` expressions without `else` evaluate to `()`
+   = help: consider adding an `else` block that evaluates to the expected type
+
+error: aborting due to 12 previous errors
 
-For more information about this error, try `rustc --explain E0317`.
+Some errors have detailed explanations: E0308, E0317.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/src/test/ui/issues/issue-19991.stderr b/src/test/ui/issues/issue-19991.stderr
index 4c6d150229a..d9ea910adef 100644
--- a/src/test/ui/issues/issue-19991.stderr
+++ b/src/test/ui/issues/issue-19991.stderr
@@ -6,11 +6,14 @@ LL | |
 LL | |
 LL | |
 LL | |         765
+   | |         --- found here
 LL | |     };
    | |_____^ expected (), found integer
    |
    = note: expected type `()`
               found type `{integer}`
+   = note: `if` expressions without `else` evaluate to `()`
+   = help: consider adding an `else` block that evaluates to the expected type
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-50577.rs b/src/test/ui/issues/issue-50577.rs
index f0f1dc6c286..bf892a8daa2 100644
--- a/src/test/ui/issues/issue-50577.rs
+++ b/src/test/ui/issues/issue-50577.rs
@@ -2,5 +2,6 @@ fn main() {
     enum Foo {
         Drop = assert_eq!(1, 1)
         //~^ ERROR if may be missing an else clause
+        //~| ERROR mismatched types [E0308]
     }
 }
diff --git a/src/test/ui/issues/issue-50577.stderr b/src/test/ui/issues/issue-50577.stderr
index 0c3ba2ea4f9..413c8c5c80b 100644
--- a/src/test/ui/issues/issue-50577.stderr
+++ b/src/test/ui/issues/issue-50577.stderr
@@ -1,3 +1,13 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-50577.rs:3:16
+   |
+LL |         Drop = assert_eq!(1, 1)
+   |                ^^^^^^^^^^^^^^^^ expected isize, found ()
+   |
+   = note: expected type `isize`
+              found type `()`
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
 error[E0317]: if may be missing an else clause
   --> $DIR/issue-50577.rs:3:16
    |
@@ -13,6 +23,7 @@ LL |         Drop = assert_eq!(1, 1)
    = help: consider adding an `else` block that evaluates to the expected type
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0317`.
+Some errors have detailed explanations: E0308, E0317.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/src/test/ui/reachable/expr_if.rs b/src/test/ui/reachable/expr_if.rs
index ed43bd8c689..a3d54892de5 100644
--- a/src/test/ui/reachable/expr_if.rs
+++ b/src/test/ui/reachable/expr_if.rs
@@ -4,7 +4,7 @@
 #![deny(unreachable_code)]
 
 fn foo() {
-    if {return} {
+    if {return} { //~ ERROR unreachable block in `if` expression
         println!("Hello, world!");
     }
 }
diff --git a/src/test/ui/reachable/expr_if.stderr b/src/test/ui/reachable/expr_if.stderr
index d11471da1a6..f1690e595e5 100644
--- a/src/test/ui/reachable/expr_if.stderr
+++ b/src/test/ui/reachable/expr_if.stderr
@@ -1,15 +1,25 @@
-error: unreachable statement
-  --> $DIR/expr_if.rs:27:5
+error: unreachable block in `if` expression
+  --> $DIR/expr_if.rs:7:17
    |
-LL |     println!("But I am.");
-   |     ^^^^^^^^^^^^^^^^^^^^^^
+LL |       if {return} {
+   |  _________________^
+LL | |         println!("Hello, world!");
+LL | |     }
+   | |_____^
    |
 note: lint level defined here
   --> $DIR/expr_if.rs:4:9
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
+
+error: unreachable statement
+  --> $DIR/expr_if.rs:27:5
+   |
+LL |     println!("But I am.");
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors