Rollup merge of rust-lang#132828 - est31:let_chains_parsing_tests, r=compiler-errors

Additional tests to ensure let is rejected during parsing

In the original stabilization PR, @ `compiler-errors` has [pointed out](rust-lang#94927 (comment)) that rust-lang#97295 wasn't enough to address the concerns about having `let` in expressions being rejected at parsing time, instead of later.

Thankfully, since then the situation has been greatly improved by rust-lang#115677. This PR adds some additional tests to `disallowed-positions.rs`, and adds two additional revisions to the "normal" case which is now given the `feature` name:

* `no_feature`: Added to incorporate `disallowed-positions-without-feature-gate.rs` into the file, reducing duplication.
* `nothing`: like feature, but all functions are cfg'd out. Ensures that the errors are really emitted during parsing.

cc tracking issue rust-lang#53667

Author: workingjubilee

tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.rs

@@ -1,3 +1,5 @@
+//@ revisions: no_feature feature nothing
+//@ edition: 2021
 // Here we test that `lowering` behaves correctly wrt. `let $pats = $expr` expressions.
 //
 // We want to make sure that `let` is banned in situations other than:
@@ -17,14 +19,16 @@
 //
 // To that end, we check some positions which is not part of the language above.
 
-#![feature(let_chains)] // Avoid inflating `.stderr` with overzealous gates in this test.
+// Avoid inflating `.stderr` with overzealous gates (or test what happens if you disable the gate)
+#![cfg_attr(not(no_feature), feature(let_chains))]
 
 #![allow(irrefutable_let_patterns)]
 
 use std::ops::Range;
 
 fn main() {}
 
+#[cfg(not(nothing))]
 fn _if() {
     if (let 0 = 1) {}
     //~^ ERROR expected expression, found `let` statement
@@ -46,8 +50,11 @@ fn _if() {
     //~^ ERROR expected expression, found `let` statement
     //~| ERROR expected expression, found `let` statement
     //~| ERROR expected expression, found `let` statement
+    //[no_feature]~| ERROR `let` expressions in this position are unstable
+    //[no_feature]~| ERROR `let` expressions in this position are unstable
 }
 
+#[cfg(not(nothing))]
 fn _while() {
     while (let 0 = 1) {}
     //~^ ERROR expected expression, found `let` statement
@@ -69,8 +76,11 @@ fn _while() {
     //~^ ERROR expected expression, found `let` statement
     //~| ERROR expected expression, found `let` statement
     //~| ERROR expected expression, found `let` statement
+    //[no_feature]~| ERROR `let` expressions in this position are unstable
+    //[no_feature]~| ERROR `let` expressions in this position are unstable
 }
 
+#[cfg(not(nothing))]
 fn _macros() {
     macro_rules! use_expr {
         ($e:expr) => {
@@ -79,11 +89,12 @@ fn _macros() {
         }
     }
     use_expr!((let 0 = 1 && 0 == 0));
-    //~^ ERROR expected expression, found `let` statement
+    //[feature,no_feature]~^ ERROR expected expression, found `let` statement
     use_expr!((let 0 = 1));
-    //~^ ERROR expected expression, found `let` statement
+    //[feature,no_feature]~^ ERROR expected expression, found `let` statement
 }
 
+#[cfg(not(nothing))]
 fn nested_within_if_expr() {
     if &let 0 = 0 {}
     //~^ ERROR expected expression, found `let` statement
@@ -97,7 +108,7 @@ fn nested_within_if_expr() {
 
     fn _check_try_binds_tighter() -> Result<(), ()> {
         if let 0 = 0? {}
-        //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+        //[feature,no_feature]~^ ERROR the `?` operator can only be applied to values that implement `Try`
         Ok(())
     }
     if (let 0 = 0)? {}
@@ -118,7 +129,7 @@ fn nested_within_if_expr() {
 
     if true..(let 0 = 0) {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
     if ..(let 0 = 0) {}
     //~^ ERROR expected expression, found `let` statement
     if (let 0 = 0).. {}
@@ -127,27 +138,54 @@ fn nested_within_if_expr() {
     // Binds as `(let ... = true)..true &&/|| false`.
     if let Range { start: _, end: _ } = true..true && false {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
     if let Range { start: _, end: _ } = true..true || false {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
 
     // Binds as `(let Range { start: F, end } = F)..(|| true)`.
     const F: fn() -> bool = || true;
     if let Range { start: F, end } = F..|| true {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
 
     // Binds as `(let Range { start: true, end } = t)..(&&false)`.
     let t = &&true;
     if let Range { start: true, end } = t..&&false {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
 
     if let true = let true = true {}
     //~^ ERROR expected expression, found `let` statement
+
+    if return let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    loop { if break let 0 = 0 {} }
+    //~^ ERROR expected expression, found `let` statement
+
+    if (match let 0 = 0 { _ => { false } }) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if (let 0 = 0, false).1 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if (let 0 = 0,) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    async fn foo() {
+        if (let 0 = 0).await {}
+        //~^ ERROR expected expression, found `let` statement
+    }
+
+    if (|| let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if (let 0 = 0)() {}
+    //~^ ERROR expected expression, found `let` statement
 }
 
+#[cfg(not(nothing))]
 fn nested_within_while_expr() {
     while &let 0 = 0 {}
     //~^ ERROR expected expression, found `let` statement
@@ -161,7 +199,7 @@ fn nested_within_while_expr() {
 
     fn _check_try_binds_tighter() -> Result<(), ()> {
         while let 0 = 0? {}
-        //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+        //[feature,no_feature]~^ ERROR the `?` operator can only be applied to values that implement `Try`
         Ok(())
     }
     while (let 0 = 0)? {}
@@ -182,7 +220,7 @@ fn nested_within_while_expr() {
 
     while true..(let 0 = 0) {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
     while ..(let 0 = 0) {}
     //~^ ERROR expected expression, found `let` statement
     while (let 0 = 0).. {}
@@ -191,27 +229,54 @@ fn nested_within_while_expr() {
     // Binds as `(let ... = true)..true &&/|| false`.
     while let Range { start: _, end: _ } = true..true && false {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
     while let Range { start: _, end: _ } = true..true || false {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
 
     // Binds as `(let Range { start: F, end } = F)..(|| true)`.
     const F: fn() -> bool = || true;
     while let Range { start: F, end } = F..|| true {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
 
     // Binds as `(let Range { start: true, end } = t)..(&&false)`.
     let t = &&true;
     while let Range { start: true, end } = t..&&false {}
     //~^ ERROR expected expression, found `let` statement
-    //~| ERROR mismatched types
+    //[feature,no_feature]~| ERROR mismatched types
 
     while let true = let true = true {}
     //~^ ERROR expected expression, found `let` statement
+
+    while return let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    'outer: loop { while break 'outer let 0 = 0 {} }
+    //~^ ERROR expected expression, found `let` statement
+
+    while (match let 0 = 0 { _ => { false } }) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while (let 0 = 0, false).1 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while (let 0 = 0,) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    async fn foo() {
+        while (let 0 = 0).await {}
+        //~^ ERROR expected expression, found `let` statement
+    }
+
+    while (|| let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while (let 0 = 0)() {}
+    //~^ ERROR expected expression, found `let` statement
 }
 
+#[cfg(not(nothing))]
 fn not_error_because_clarified_intent() {
     if let Range { start: _, end: _ } = (true..true || false) { }
 
@@ -222,6 +287,7 @@ fn not_error_because_clarified_intent() {
     while let Range { start: _, end: _ } = (true..true && false) { }
 }
 
+#[cfg(not(nothing))]
 fn outside_if_and_while_expr() {
     &let 0 = 0;
     //~^ ERROR expected expression, found `let` statement
@@ -232,10 +298,12 @@ fn outside_if_and_while_expr() {
     //~^ ERROR expected expression, found `let` statement
     -let 0 = 0;
     //~^ ERROR expected expression, found `let` statement
+    let _ = let _ = 3;
+    //~^ ERROR expected expression, found `let` statement
 
     fn _check_try_binds_tighter() -> Result<(), ()> {
         let 0 = 0?;
-        //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+        //[feature,no_feature]~^ ERROR the `?` operator can only be applied to values that implement `Try`
         Ok(())
     }
     (let 0 = 0)?;
@@ -260,8 +328,8 @@ fn outside_if_and_while_expr() {
     //~^ ERROR expected expression, found `let` statement
 
     (let Range { start: _, end: _ } = true..true || false);
-    //~^ ERROR mismatched types
-    //~| ERROR expected expression, found `let` statement
+    //~^ ERROR expected expression, found `let` statement
+    //[feature,no_feature]~| ERROR mismatched types
 
     (let true = let true = true);
     //~^ ERROR expected expression, found `let` statement
@@ -285,6 +353,7 @@ fn outside_if_and_while_expr() {
 }
 
 // Let's make sure that `let` inside const generic arguments are considered.
+#[cfg(not(nothing))]
 fn inside_const_generic_arguments() {
     struct A<const B: bool>;
     impl<const B: bool> A<{B}> { const O: u32 = 5; }
@@ -317,6 +386,7 @@ fn inside_const_generic_arguments() {
     >::O == 5 {}
 }
 
+#[cfg(not(nothing))]
 fn with_parenthesis() {
     let opt = Some(Some(1i32));
 
@@ -332,6 +402,7 @@ fn with_parenthesis() {
     //~| ERROR expected expression, found `let` statement
     }
     if let Some(a) = opt && (true && true) {
+    //[no_feature]~^ ERROR `let` expressions in this position are unstable
     }
 
     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
@@ -347,14 +418,18 @@ fn with_parenthesis() {
     }
 
     if (true && (true)) && let Some(a) = opt {
+    //[no_feature]~^ ERROR `let` expressions in this position are unstable
     }
     if (true) && let Some(a) = opt {
+    //[no_feature]~^ ERROR `let` expressions in this position are unstable
     }
     if true && let Some(a) = opt {
+    //[no_feature]~^ ERROR `let` expressions in this position are unstable
     }
 
     let fun = || true;
     if let true = (true && fun()) && (true) {
+    //[no_feature]~^ ERROR `let` expressions in this position are unstable
     }
 
     #[cfg(FALSE)]