Auto merge of #111928 - c410-f3r:dqewdas, r=eholk

[RFC-2011] Expand more expressions

cc #44838

Expands `if`, `let`, `match` and also makes `generic_assert_internals` an allowed feature when using `assert!`. `#![feature(generic_assert)]` is still needed to activate everything.

```rust
#![feature(generic_assert)]

fn fun(a: Option<i32>, b: Option<i32>, c: Option<i32>) {
  assert!(
    if a.is_some() { 1 } else { 2 } == 3
      && if let Some(elem) = b { elem == 4 } else { false }
      && match c { Some(_) => true, None => false }
  );
}

fn main() {
  fun(Some(1), None, Some(2));
}

// Assertion failed: assert!(
//   if a.is_some() { 1 } else { 2 } == 3
//     && if let Some(elem) = b { elem == 4 } else { false }
//     && match c { Some(_) => true, None => false }
// );
//
// With captures:
//   a = Some(1)
//   b = None
//   c = Some(2)
```

1 files changed, 11 insertions, 5 deletions

diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index ea830a0ce60..b619e80e15f 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -233,10 +233,19 @@ impl<'cx, 'a> Context<'cx, 'a> {
             ExprKind::Cast(local_expr, _) => {
                 self.manage_cond_expr(local_expr);
             }
+            ExprKind::If(local_expr, _, _) => {
+                self.manage_cond_expr(local_expr);
+            }
             ExprKind::Index(prefix, suffix) => {
                 self.manage_cond_expr(prefix);
                 self.manage_cond_expr(suffix);
             }
+            ExprKind::Let(_, local_expr, _) => {
+                self.manage_cond_expr(local_expr);
+            }
+            ExprKind::Match(local_expr, _) => {
+                self.manage_cond_expr(local_expr);
+            }
             ExprKind::MethodCall(call) => {
                 for arg in &mut call.args {
                     self.manage_cond_expr(arg);
@@ -295,17 +304,14 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::Continue(_)
             | ExprKind::Err
             | ExprKind::Field(_, _)
-            | ExprKind::FormatArgs(_)
             | ExprKind::ForLoop(_, _, _, _)
-            | ExprKind::If(_, _, _)
+            | ExprKind::FormatArgs(_)
             | ExprKind::IncludedBytes(..)
             | ExprKind::InlineAsm(_)
-            | ExprKind::OffsetOf(_, _)
-            | ExprKind::Let(_, _, _)
             | ExprKind::Lit(_)
             | ExprKind::Loop(_, _, _)
             | ExprKind::MacCall(_)
-            | ExprKind::Match(_, _)
+            | ExprKind::OffsetOf(_, _)
             | ExprKind::Path(_, _)
             | ExprKind::Ret(_)
             | ExprKind::Try(_)