Remove attributes and comments before let on calculating available space in let-else statement

Author: rhysd

src/items.rs

@@ -154,11 +154,21 @@ impl Rewrite for ast::Local {
                     std::cmp::min(shape.width, context.config.single_line_let_else_max_width());
 
                 // If available_space hits zero we know for sure this will be a multi-lined block
-                let available_space = max_width.saturating_sub(result.len());
+                let assign_len = if context.config.version() == Version::Two {
+                    result.len() - let_kw_offset
+                } else {
+                    result.len()
+                };
+                let available_space = max_width.saturating_sub(assign_len);
 
+                let assign_str = if context.config.version() == Version::Two {
+                    &result[let_kw_offset..]
+                } else {
+                    result.as_str()
+                };
                 let allow_single_line = !force_newline_else
                     && available_space > 0
-                    && allow_single_line_let_else_block(&result, block);
+                    && allow_single_line_let_else_block(assign_str, block);
 
                 let mut rw_else_block =
                     rewrite_let_else_block(block, allow_single_line, context, shape)?;

tests/source/let_else.rs

@@ -172,4 +172,11 @@ fn issue5901() {
     #[cfg(target_os = "linux")]
     #[cfg(target_arch = "x86_64")]
     let Some(x) = foo else { return; };
+
+    // The else block will be multi-lined because attributes and comments before `let`
+    // are included when calculating max width
+    #[cfg(target_os = "linux")]
+    #[cfg(target_arch = "x86_64")]
+    // Some comments between attributes and let-else statement
+    let Some(x) = foo() else { todo!() };
 }

tests/source/let_else_v2.rs

@@ -1,4 +1,5 @@
 // rustfmt-version: Two
+// rustfmt-single_line_let_else_max_width: 100
 
 fn issue5901() {
     #[cfg(target_os = "linux")]
@@ -11,4 +12,11 @@ fn issue5901() {
     #[cfg(target_os = "linux")]
     #[cfg(target_arch = "x86_64")]
     let Some(x) = foo else { return; };
+
+    // The else block will be signle-lined because attributes and comments before `let`
+    // are no longer included when calculating max width
+    #[cfg(target_os = "linux")]
+    #[cfg(target_arch = "x86_64")]
+    // Some comments between attributes and let-else statement
+    let Some(x) = foo else { todo!() };
 }

tests/target/let_else.rs

@@ -273,4 +273,13 @@ fn issue5901() {
     else {
         return;
     };
+
+    // The else block will be multi-lined because attributes and comments before `let`
+    // are included when calculating max width
+    #[cfg(target_os = "linux")]
+    #[cfg(target_arch = "x86_64")]
+    // Some comments between attributes and let-else statement
+    let Some(x) = foo() else {
+        todo!()
+    };
 }

tests/target/let_else_v2.rs

@@ -1,4 +1,5 @@
 // rustfmt-version: Two
+// rustfmt-single_line_let_else_max_width: 100
 
 fn issue5901() {
     #[cfg(target_os = "linux")]
@@ -17,4 +18,11 @@ fn issue5901() {
     let Some(x) = foo else {
         return;
     };
+
+    // The else block will be signle-lined because attributes and comments before `let`
+    // are no longer included when calculating max width
+    #[cfg(target_os = "linux")]
+    #[cfg(target_arch = "x86_64")]
+    // Some comments between attributes and let-else statement
+    let Some(x) = foo else { todo!() };
 }