enhance const block formatting (#4493)

Signed-off-by: frbimo <[email protected]>

Author: frbimo

src/formatting/expr.rs

@@ -125,7 +125,32 @@ pub(crate) fn format_expr(
         | ast::ExprKind::While(..) => to_control_flow(expr, expr_type)
             .and_then(|control_flow| control_flow.rewrite(context, shape)),
         ast::ExprKind::ConstBlock(ref anon_const) => {
-            Some(format!("const {}", anon_const.rewrite(context, shape)?))
+            let between_span = mk_sp(
+                context.snippet_provider.span_after(expr.span, "const"),
+                anon_const.value.span.lo(),
+            );
+            let anon_const_str = anon_const.rewrite(context, shape)?;
+            let contains_comments =
+                contains_comment(context.snippet_provider.span_to_snippet(between_span)?);
+            match context.config.brace_style() {
+                BraceStyle::AlwaysNextLine => combine_strs_with_missing_comments(
+                    context,
+                    "const",
+                    &anon_const_str,
+                    between_span,
+                    shape,
+                    !anon_const_str.contains('\n'),
+                ),
+                _ if !contains_comments => Some(format!("const {}", &anon_const_str)),
+                _ => combine_strs_with_missing_comments(
+                    context,
+                    "const",
+                    &anon_const_str,
+                    between_span,
+                    shape,
+                    true,
+                ),
+            }
         }
         ast::ExprKind::Block(ref block, opt_label) => {
             match expr_type {

tests/source/configs/brace_style/const_block_always_next_line.rs

@@ -0,0 +1,45 @@
+// rustfmt-brace_style: AlwaysNextLine
+// AlwaysNextLine brace style for const blocks
+
+fn foo() -> i32 {
+    const {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn bar() -> i32 {
+    const { 4 }
+}
+
+fn foo() -> i32 {
+    const
+{
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const // baz
+{
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const /*qux */ {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const
+// baz
+{
+        let x = 5 + 10;
+        x / 3
+    }
+}

tests/source/configs/brace_style/const_block_same_line_where.rs

@@ -0,0 +1,45 @@
+// rustfmt-brace_style: SameLineWhere
+// SameLineWhere brace style for const blocks
+
+fn foo() -> i32 {
+    const {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn bar() -> i32 {
+    const { 4 }
+}
+
+fn foo() -> i32 {
+    const
+{
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const // baz
+{
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const /*qux */ {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const
+// baz
+{
+        let x = 5 + 10;
+        x / 3
+    }
+}

tests/target/configs/brace_style/const_block_always_next_line.rs

@@ -0,0 +1,53 @@
+// rustfmt-brace_style: AlwaysNextLine
+// AlwaysNextLine brace style for const blocks
+
+fn foo() -> i32
+{
+    const
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn bar() -> i32
+{
+    const { 4 }
+}
+
+fn foo() -> i32
+{
+    const
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32
+{
+    const // baz
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32
+{
+    const /*qux */
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32
+{
+    const
+    // baz
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}

tests/target/configs/brace_style/const_block_same_line_where.rs

@@ -0,0 +1,45 @@
+// rustfmt-brace_style: SameLineWhere
+// SameLineWhere brace style for const blocks
+
+fn foo() -> i32 {
+    const {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn bar() -> i32 {
+    const { 4 }
+}
+
+fn foo() -> i32 {
+    const {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const // baz
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const /*qux */
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}
+
+fn foo() -> i32 {
+    const
+    // baz
+    {
+        let x = 5 + 10;
+        x / 3
+    }
+}