chains: prefer to use the next line for an expression, if using the same line would...

This problem came to light due to the chains changes, but effects other code too. It only happens rarely, e.g.,

before this fix:
```
    match foo {
        MacroArgKind::Delimited(ref delim_tok, ref args) => rewrite_delimited_inner(
            delim_tok,
            args,
        ).map(|(lhs, inner, rhs)| format!("{}{}{}", lhs, inner, rhs)),
    };

```

after:
```
    match foo {
        MacroArgKind::Delimited(ref delim_tok, ref args) => {
            rewrite_delimited_inner(delim_tok, args)
                .map(|(lhs, inner, rhs)| format!("{}{}{}", lhs, inner, rhs))
        }
    }

```

diff --git a/src/chains.rs b/src/chains.rs
index 81be8d54128705281b2cf35dca8c46f75a4864f0..d7126b2f5e798c5035ef4b6fb1678eb33f90e8e9 100644 (file)
--- a/src/chains.rs
+++ b/src/chains.rs
@@ -398,8 +398,8 @@ fn format_last_child(&mut self, may_extend: bool, context: &RewriteContext, shap
         if all_in_one_line || extendable {
             // First we try to 'overflow' the last child and see if it looks better than using
             // vertical layout.
-            if let Some(shape) = last_shape.offset_left(almost_total) {
-                if let Some(rw) = last.rewrite_postfix(context, shape) {
+            if let Some(one_line_shape) = last_shape.offset_left(almost_total) {
+                if let Some(rw) = last.rewrite_postfix(context, one_line_shape) {
                     // We allow overflowing here only if both of the following conditions match:
                     // 1. The entire chain fits in a single line except the last child.
                     // 2. `last_child_str.lines().count() >= 5`.
@@ -413,6 +413,7 @@ fn format_last_child(&mut self, may_extend: bool, context: &RewriteContext, shap
                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
                         // last child on its own line, and compare two rewrites to choose which is
                         // better.
+                        let last_shape = child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?;
                         match last.rewrite_postfix(context, last_shape) {
                             Some(ref new_rw) if !could_fit_single_line => {
                                 last_subexpr_str = Some(new_rw.clone());

diff --git a/src/expr.rs b/src/expr.rs
index 6e1af266e9bfe8e9dfb95470a6fc1e3edef01c5a..8aa5d9bd286448ed8fc9f0ba3ba3c6799bf5fab4 100644 (file)
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -39,9 +39,9 @@
 use string::{rewrite_string, StringFormat};
 use types::{can_be_overflowed_type, rewrite_path, PathContext};
 use utils::{
-    colon_spaces, contains_skip, count_newlines, first_line_width, inner_attributes,
-    last_line_extendable, last_line_width, mk_sp, outer_attributes, ptr_vec_to_ref_vec,
-    semicolon_for_stmt, wrap_str,
+    colon_spaces, contains_skip, count_newlines, first_line_ends_with, first_line_width,
+    inner_attributes, last_line_extendable, last_line_width, mk_sp, outer_attributes,
+    ptr_vec_to_ref_vec, semicolon_for_stmt, wrap_str,
 };
 use vertical::rewrite_with_alignment;
 use visitor::FmtVisitor;
@@ -1953,6 +1953,9 @@ pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTac
     rhs_tactics == RhsTactics::ForceNextLineWithoutIndent
         || !next_line_rhs.contains('\n')
         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
+        || first_line_ends_with(orig_rhs, '(') && !first_line_ends_with(next_line_rhs, '(')
+        || first_line_ends_with(orig_rhs, '{') && !first_line_ends_with(next_line_rhs, '{')
+        || first_line_ends_with(orig_rhs, '[') && !first_line_ends_with(next_line_rhs, '[')
 }
 
 fn rewrite_expr_addrof(

diff --git a/src/utils.rs b/src/utils.rs
index f1b0582b1200f539cc433c6751ee8ab0bea2bc95..b8474792cd3040117398a402512288736d5e97be 100644 (file)
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -382,6 +382,7 @@ pub fn colon_spaces(before: bool, after: bool) -> &'static str {
     }
 }
 
+#[inline]
 pub fn left_most_sub_expr(e: &ast::Expr) -> &ast::Expr {
     match e.node {
         ast::ExprKind::Call(ref e, _)
@@ -398,6 +399,12 @@ pub fn left_most_sub_expr(e: &ast::Expr) -> &ast::Expr {
     }
 }
 
+#[inline]
 pub fn starts_with_newline(s: &str) -> bool {
     s.starts_with('\n') || s.starts_with("\r\n")
 }
+
+#[inline]
+pub fn first_line_ends_with(s: &str, c: char) -> bool {
+    s.lines().next().map_or(false, |l| l.ends_with(c))
+}