Improve HIR pretty-printing of if/else some more.

In the AST the "then" block is represented as a `Block`. In HIR the
"then" block is represented as an `Expr` that happens to always be.
`ExprKind::Block`. By deconstructing the `ExprKind::Block` to extract
the block within, things print properly.

For `issue-82392.rs`, note that we no longer print a type after the
"then" block. This is good, it now matches how we don't print a type for
the "else" block. (Well, we do print a type after the "else" block, but
it's for the whole if/else.)

Also tighten up some of the pattern matching -- these block expressions
within if/else will never have labels.

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -30,7 +30,7 @@ impl<'a> State<'a> {
                     self.print_else(e.as_deref())
                 }
                 // Final `else` block.
-                ast::ExprKind::Block(b, _) => {
+                ast::ExprKind::Block(b, None) => {
                     self.cbox(0);
                     self.ibox(0);
                     self.word(" else ");

compiler/rustc_hir_pretty/src/lib.rs

@@ -1064,17 +1064,17 @@ impl<'a> State<'a> {
         if let Some(els_inner) = els {
             match els_inner.kind {
                 // Another `else if` block.
-                hir::ExprKind::If(i, then, e) => {
+                hir::ExprKind::If(i, hir::Expr { kind: hir::ExprKind::Block(t, None), .. }, e) => {
                     self.cbox(0);
                     self.ibox(0);
                     self.word(" else if ");
                     self.print_expr_as_cond(i);
                     self.space();
-                    self.print_expr(then);
+                    self.print_block(t);
                     self.print_else(e);
                 }
                 // Final `else` block.
-                hir::ExprKind::Block(b, _) => {
+                hir::ExprKind::Block(b, None) => {
                     self.cbox(0);
                     self.ibox(0);
                     self.word(" else ");
@@ -1099,8 +1099,13 @@ impl<'a> State<'a> {
         self.word_nbsp("if");
         self.print_expr_as_cond(test);
         self.space();
-        self.print_expr(blk);
-        self.print_else(elseopt)
+        match blk.kind {
+            hir::ExprKind::Block(blk, None) => {
+                self.print_block(blk);
+                self.print_else(elseopt)
+            }
+            _ => panic!("non-block then expr"),
+        }
     }
 
     fn print_anon_const(&mut self, constant: &hir::AnonConst) {

tests/pretty/hir-if-else.pp

@@ -12,37 +12,28 @@ fn f(x: u32,
     let mut a = 0;
     if x > y { a = 1; } else { a = 2; }
 
-        if x < 1
-            {
-                a = 1;
-            } else if x < 2
-            {
-                a = 2;
-            } else if x < 3
-            {
-                a = 3;
-            } else if x < 4 { a = 4; } else { a = 5; }
+    if x < 1 {
+        a = 1;
+    } else if x < 2 {
+        a = 2;
+    } else if x < 3 { a = 3; } else if x < 4 { a = 4; } else { a = 5; }
 
-            if x < y
-                {
-                    a += 1;
-                    a += 1;
-                    a += 1;
-                    a += 1;
-                    a += 1;
-                    a += 1;
-                } else { a += 1; a += 1; a += 1; a += 1; a += 1; a += 1; }
+    if x < y {
+        a += 1;
+        a += 1;
+        a += 1;
+        a += 1;
+        a += 1;
+        a += 1;
+    } else { a += 1; a += 1; a += 1; a += 1; a += 1; a += 1; }
 
-                if x < 1
-                    {
-                        if x < 2
-                            {
-                                if x < 3
-                                    {
-                                        a += 1;
-                                    } else if x < 4
-                                    { a += 1; if x < 5 { a += 1; } }
-                                    } else if x < 6 { a += 1; } }
-                                }
+    if x < 1 {
+        if x < 2 {
+            if x < 3 {
+                a += 1;
+            } else if x < 4 { a += 1; if x < 5 { a += 1; } }
+        } else if x < 6 { a += 1; }
+    }
+}
 
-                                fn main() { f(3, 4); }
+fn main() { f(3, 4); }

tests/ui/match/issue-82392.stdout

@@ -8,10 +8,10 @@ extern crate std;
 //@ edition:2015
 
 fn main() ({
-    (if (true as bool)
-        ({ } as
-            ()) else if (let Some(a) =
+    (if (true as bool) {
+    } else if (let Some(a) =
             ((Some as
                     fn(i32) -> Option<i32> {Option::<i32>::Some})((3 as i32)) as
-                Option<i32>) as bool) ({ } as ()) as ())
+                Option<i32>) as bool) {
     } as ())
+} as ())