Rollup merge of rust-lang#140486 - calebcartwright:rustfmt-let-chain-bool-lit, r=calebcartwright

rustfmt: Also allow bool literals as first item of let chain

This is a functional cherry-pick of rust-lang/rustfmt#6492

I'm bringing this change over directly as the subtree sync is taking more effort than anticipated (some unrelated r-l/rustfmt changes need to be reverted before we perform the full sync) and we need to ensure that rustfmt behavior accounts with the final style guide rules as part of let chain stabilization.

r? `@ghost`

Author: Zalathar

src/tools/rustfmt/src/pairs.rs

@@ -1,4 +1,4 @@
-use rustc_ast::ast;
+use rustc_ast::{ast, token};
 use rustc_span::Span;
 
 use crate::config::IndentStyle;
@@ -272,13 +272,17 @@ struct PairList<'a, 'b, T: Rewrite> {
     span: Span,
 }
 
-fn is_ident(expr: &ast::Expr) -> bool {
+fn is_ident_or_bool_lit(expr: &ast::Expr) -> bool {
     match &expr.kind {
         ast::ExprKind::Path(None, path) if path.segments.len() == 1 => true,
+        ast::ExprKind::Lit(token::Lit {
+            kind: token::LitKind::Bool,
+            ..
+        }) => true,
         ast::ExprKind::Unary(_, expr)
         | ast::ExprKind::AddrOf(_, _, expr)
         | ast::ExprKind::Paren(expr)
-        | ast::ExprKind::Try(expr) => is_ident(expr),
+        | ast::ExprKind::Try(expr) => is_ident_or_bool_lit(expr),
         _ => false,
     }
 }
@@ -296,10 +300,10 @@ impl<'a, 'b> PairList<'a, 'b, ast::Expr> {
             return false;
         }
 
-        let fist_item_is_ident = is_ident(self.list[0].0);
+        let fist_item_is_ident_or_bool_lit = is_ident_or_bool_lit(self.list[0].0);
         let second_item_is_let_chain = matches!(self.list[1].0.kind, ast::ExprKind::Let(..));
 
-        fist_item_is_ident && second_item_is_let_chain
+        fist_item_is_ident_or_bool_lit && second_item_is_let_chain
     }
 }
 

src/tools/rustfmt/tests/source/let_chains.rs

@@ -20,6 +20,11 @@ fn test_single_line_let_chain() {
     if a && let Some(b) = foo() {
     }
 
+    // first item in let-chain is a bool literal
+    if true && let Some(x) = y {
+
+    }
+
     // first item in let-chain is a unary ! with an ident
     let unary_not = if !from_hir_call
         && let Some(p) = parent
@@ -94,11 +99,6 @@ fn test_multi_line_let_chain() {
 
     }
 
-    // bool literal
-    if true && let Some(x) = y {
-
-    }
-
     // cast to a bool
     if 1 as bool && let Some(x) = y {
 

src/tools/rustfmt/tests/target/let_chains.rs

@@ -50,6 +50,9 @@ fn test_single_line_let_chain() {
     // first item in let-chain is an ident
     if a && let Some(b) = foo() {}
 
+    // first item in let-chain is a bool literal
+    if true && let Some(x) = y {}
+
     // first item in let-chain is a unary ! with an ident
     let unary_not = if !from_hir_call && let Some(p) = parent {};
 
@@ -102,11 +105,6 @@ fn test_multi_line_let_chain() {
         && let Some(x) = y
     {}
 
-    // bool literal
-    if true
-        && let Some(x) = y
-    {}
-
     // cast to a bool
     if 1 as bool
         && let Some(x) = y