Enhance comment formatting

Cargo.toml

@@ -7,7 +7,7 @@ description = "Tool to find and fix Rust formatting issues"
 repository = "https://github.com/rust-lang-nursery/rustfmt"
 readme = "README.md"
 license = "Apache-2.0/MIT"
-include = ["src/*.rs", "Cargo.toml", "build.rs", "LICENSE-*"]
+include = ["src/**", "Cargo.toml", "build.rs", "LICENSE-*"]
 build = "build.rs"
 categories = ["development-tools"]
 

src/comment.rs

@@ -153,11 +153,10 @@ pub fn combine_strs_with_missing_comments(
     let mut one_line_width =
         last_line_width(prev_str) + first_line_width(next_str) + first_sep.len();
 
-    let original_snippet = context.snippet(span);
-    let trimmed_snippet = original_snippet.trim();
     let indent_str = shape.indent.to_string(context.config);
+    let missing_comment = try_opt!(rewrite_missing_comment(span, shape, context));
 
-    if trimmed_snippet.is_empty() {
+    if missing_comment.is_empty() {
         if allow_extend && prev_str.len() + first_sep.len() + next_str.len() <= shape.width {
             return Some(format!("{}{}{}", prev_str, first_sep, next_str));
         } else {
@@ -175,18 +174,13 @@ pub fn combine_strs_with_missing_comments(
     // Peek the the original source code and find out whether there is a newline between the first
     // expression and the second expression or the missing comment. We will preserve the orginal
     // layout whenever possible.
+    let original_snippet = context.snippet(span);
     let prefer_same_line = if let Some(pos) = original_snippet.chars().position(|c| c == '/') {
         !original_snippet[..pos].contains('\n')
     } else {
         !original_snippet.contains('\n')
     };
 
-    let missing_comment = try_opt!(rewrite_comment(
-        trimmed_snippet,
-        false,
-        shape,
-        context.config
-    ));
     one_line_width -= first_sep.len();
     let first_sep = if prev_str.is_empty() || missing_comment.is_empty() {
         String::new()
@@ -365,6 +359,50 @@ fn rewrite_comment_inner(
     Some(result)
 }
 
+/// Given the span, rewrite the missing comment inside it if available.
+/// Note that the given span must only include comments (or leading/trailing whitespaces).
+pub fn rewrite_missing_comment(
+    span: Span,
+    shape: Shape,
+    context: &RewriteContext,
+) -> Option<String> {
+    let missing_snippet = context.snippet(span);
+    let trimmed_snippet = missing_snippet.trim();
+    if !trimmed_snippet.is_empty() {
+        rewrite_comment(trimmed_snippet, false, shape, context.config)
+    } else {
+        Some(String::new())
+    }
+}
+
+/// Recover the missing comments in the specified span, if available.
+/// The layout of the comments will be preserved as long as it does not break the code
+/// and its total width does not exceed the max width.
+pub fn recover_missing_comment_in_span(
+    span: Span,
+    shape: Shape,
+    context: &RewriteContext,
+    used_width: usize,
+) -> Option<String> {
+    let missing_comment = try_opt!(rewrite_missing_comment(span, shape, context));
+    if missing_comment.is_empty() {
+        Some(String::new())
+    } else {
+        let missing_snippet = context.snippet(span);
+        let pos = missing_snippet.chars().position(|c| c == '/').unwrap_or(0);
+        // 1 = ` `
+        let total_width = missing_comment.len() + used_width + 1;
+        let force_new_line_before_comment =
+            missing_snippet[..pos].contains('\n') || total_width > context.config.max_width();
+        let sep = if force_new_line_before_comment {
+            format!("\n{}", shape.indent.to_string(context.config))
+        } else {
+            String::from(" ")
+        };
+        Some(format!("{}{}", sep, missing_comment))
+    }
+}
+
 /// Trims whitespace and aligns to indent, but otherwise does not change comments.
 fn light_rewrite_comment(orig: &str, offset: Indent, config: &Config) -> Option<String> {
     let lines: Vec<&str> = orig.lines()

src/expr.rs

@@ -20,7 +20,7 @@ use {Indent, Shape, Spanned};
 use chains::rewrite_chain;
 use codemap::{LineRangeUtils, SpanUtils};
 use comment::{combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
-              rewrite_comment, FindUncommented};
+              rewrite_comment, rewrite_missing_comment, FindUncommented};
 use config::{Config, ControlBraceStyle, IndentStyle, MultilineStyle, Style};
 use items::{span_hi_for_arg, span_lo_for_arg};
 use lists::{definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting,
@@ -1195,9 +1195,13 @@ impl<'a> ControlFlow<'a> {
             mk_sp(self.block.span.lo, self.block.span.lo)
         };
 
-        // for event in event
+        // `for event in event`
+        // Do not include label in the span.
+        let lo = self.label.map_or(self.span.lo, |label| label.span.hi);
         let between_kwd_cond = mk_sp(
-            context.codemap.span_after(self.span, self.keyword.trim()),
+            context
+                .codemap
+                .span_after(mk_sp(lo, self.span.hi), self.keyword.trim()),
             self.pat
                 .map_or(cond_span.lo, |p| if self.matcher.is_empty() {
                     p.span.lo
@@ -1378,21 +1382,13 @@ fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
 }
 
 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
-    let comment_str = context.snippet(span);
-    if contains_comment(&comment_str) {
-        let comment = try_opt!(rewrite_comment(
-            comment_str.trim(),
-            false,
-            shape,
-            context.config,
-        ));
-        Some(format!(
+    match rewrite_missing_comment(span, shape, context) {
+        Some(ref comment) if !comment.is_empty() => Some(format!(
             "\n{indent}{}\n{indent}",
             comment,
             indent = shape.indent.to_string(context.config)
-        ))
-    } else {
-        None
+        )),
+        _ => None,
     }
 }