Fix handling of code that is annotated with rustfmt::skip.

A rustfmt::skip'ed block is indented although original lines are
returned. In order to resolve this, the leading whitespaces are trimmed
on each line while retaining the layout; this leaves the skipped code
to be indented as necessary by the caller.

src/comment.rs

@@ -19,7 +19,7 @@ use config::Config;
 use rewrite::RewriteContext;
 use shape::{Indent, Shape};
 use string::{rewrite_string, StringFormat};
-use utils::{count_newlines, first_line_width, last_line_width};
+use utils::{count_newlines, first_line_width, last_line_width, trim_left_preserve_layout};
 use {ErrorKind, FormattingError};
 
 fn is_custom_comment(comment: &str) -> bool {
@@ -332,12 +332,12 @@ fn identify_comment(
     let (first_group, rest) = orig.split_at(first_group_ending);
     let rewritten_first_group =
         if !config.normalize_comments() && has_bare_lines && style.is_block_comment() {
-            light_rewrite_block_comment_with_bare_lines(first_group, shape, config)?
+            trim_left_preserve_layout(first_group, &shape.indent, config)
         } else if !config.normalize_comments()
             && !config.wrap_comments()
             && !config.format_doc_comments()
         {
-            light_rewrite_comment(first_group, shape.indent, config, is_doc_comment)?
+            light_rewrite_comment(first_group, shape.indent, config, is_doc_comment)
         } else {
             rewrite_comment_inner(
                 first_group,
@@ -370,47 +370,6 @@ fn identify_comment(
     }
 }
 
-/// Trims a minimum of leading whitespaces so that the content layout is kept and aligns to indent.
-fn light_rewrite_block_comment_with_bare_lines(
-    orig: &str,
-    shape: Shape,
-    config: &Config,
-) -> Option<String> {
-    let prefix_whitespace_min = orig
-        .lines()
-        // skip the line with the starting sigil since the leading whitespace is removed
-        // otherwise, the minimum would always be zero
-        .skip(1)
-        .filter(|line| !line.is_empty())
-        .map(|line| {
-            let mut width = 0;
-            for c in line.chars() {
-                match c {
-                    ' ' => width += 1,
-                    '\t' => width += config.tab_spaces(),
-                    _ => break,
-                }
-            }
-            width
-        })
-        .min()?;
-
-    let indent_str = shape.indent.to_string(config);
-    let mut lines = orig.lines();
-    let first_line = lines.next()?;
-    let rest = lines
-        .map(|line| {
-            if line.is_empty() {
-                line
-            } else {
-                &line[prefix_whitespace_min..]
-            }
-        })
-        .collect::<Vec<&str>>()
-        .join(&format!("\n{}", indent_str));
-    Some(format!("{}\n{}{}", first_line, indent_str, rest))
-}
-
 /// Attributes for code blocks in rustdoc.
 /// See https://doc.rust-lang.org/rustdoc/print.html#attributes
 enum CodeBlockAttribute {
@@ -912,7 +871,7 @@ fn light_rewrite_comment(
     offset: Indent,
     config: &Config,
     is_doc_comment: bool,
-) -> Option<String> {
+) -> String {
     let lines: Vec<&str> = orig
         .lines()
         .map(|l| {
@@ -933,7 +892,7 @@ fn light_rewrite_comment(
             trim_right_unless_two_whitespaces(left_trimmed, is_doc_comment)
         })
         .collect();
-    Some(lines.join(&format!("\n{}", offset.to_string(config))))
+    lines.join(&format!("\n{}", offset.to_string(config)))
 }
 
 /// Trims comment characters and possibly a single space from the left of a string.

src/utils.rs

@@ -21,8 +21,9 @@ use syntax::ptr;
 use syntax::source_map::{BytePos, Span, NO_EXPANSION};
 
 use comment::{filter_normal_code, CharClasses, FullCodeCharKind};
+use config::Config;
 use rewrite::RewriteContext;
-use shape::Shape;
+use shape::{Indent, Shape};
 
 pub const DEPR_SKIP_ANNOTATION: &str = "rustfmt_skip";
 pub const SKIP_ANNOTATION: &str = "rustfmt::skip";
@@ -482,6 +483,44 @@ pub fn remove_trailing_white_spaces(text: &str) -> String {
     buffer
 }
 
+/// Trims a minimum of leading whitespaces so that the content layout is kept and aligns to indent.
+pub fn trim_left_preserve_layout(orig: &str, indent: &Indent, config: &Config) -> String {
+    let prefix_whitespace_min = orig
+        .lines()
+        // skip the line with the starting sigil since the leading whitespace is removed
+        // otherwise, the minimum would always be zero
+        .skip(1)
+        .filter(|line| !line.is_empty())
+        .map(|line| {
+            let mut width = 0;
+            for c in line.chars() {
+                match c {
+                    ' ' => width += 1,
+                    '\t' => width += config.tab_spaces(),
+                    _ => break,
+                }
+            }
+            width
+        })
+        .min()
+        .unwrap_or(0);
+
+    let indent_str = indent.to_string(config);
+    let mut lines = orig.lines();
+    let first_line = lines.next().unwrap();
+    let rest = lines
+        .map(|line| {
+            if line.is_empty() {
+                String::from("\n")
+            } else {
+                format!("\n{}{}", indent_str, &line[prefix_whitespace_min..])
+            }
+        })
+        .collect::<Vec<String>>()
+        .concat();
+    format!("{}{}", first_line, rest)
+}
+
 #[test]
 fn test_remove_trailing_white_spaces() {
     let s = "    r#\"\n        test\n    \"#";

src/visitor.rs

@@ -29,7 +29,7 @@ use source_map::{LineRangeUtils, SpanUtils};
 use spanned::Spanned;
 use utils::{
     self, contains_skip, count_newlines, inner_attributes, mk_sp, ptr_vec_to_ref_vec,
-    rewrite_ident, DEPR_SKIP_ANNOTATION,
+    rewrite_ident, trim_left_preserve_layout, DEPR_SKIP_ANNOTATION,
 };
 use {ErrorKind, FormatReport, FormattingError};
 
@@ -574,9 +574,16 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
     }
 
     #[allow(clippy::needless_pass_by_value)]
-    fn push_rewrite_inner(&mut self, span: Span, rewrite: Option<String>) {
+    fn push_rewrite_inner(&mut self, span: Span, rewrite: Option<String>, is_skipped: bool) {
         if let Some(ref s) = rewrite {
             self.push_str(s);
+        } else if is_skipped {
+            // in case the code block (e.g., inside a macro or a doc) is skipped a minimum of
+            // leading whitespaces is trimmed so that the code layout is kept but allows it to
+            // be indented as necessary
+            let snippet =
+                trim_left_preserve_layout(self.snippet(span), &self.block_indent, self.config);
+            self.push_str(&snippet);
         } else {
             let snippet = self.snippet(span);
             self.push_str(snippet);
@@ -586,13 +593,13 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
 
     pub fn push_rewrite(&mut self, span: Span, rewrite: Option<String>) {
         self.format_missing_with_indent(source!(self, span).lo());
-        self.push_rewrite_inner(span, rewrite);
+        self.push_rewrite_inner(span, rewrite, false);
     }
 
     pub fn push_skipped_with_span(&mut self, span: Span) {
         self.format_missing_with_indent(source!(self, span).lo());
         let lo = self.line_number + 1;
-        self.push_rewrite_inner(span, None);
+        self.push_rewrite_inner(span, None, true);
         let hi = self.line_number + 1;
         self.skipped_range.push((lo, hi));
     }

tests/source/issue-3105.rs

@@ -0,0 +1,30 @@
+// rustfmt-wrap_comments: true
+
+/// ```
+/// pub unsafe fn _mm256_shufflehi_epi16(a: __m256i, imm8: i32) -> __m256i {
+///     let imm8 = (imm8 & 0xFF) as u8;
+///     let a = a.as_i16x16();
+///     macro_rules! shuffle_done {
+///         ($x01:expr, $x23:expr, $x45:expr, $x67:expr) => {
+///             #[cfg_attr(rustfmt, rustfmt_skip)]
+///       simd_shuffle16(a, a, [
+///           0, 1, 2, 3, 4+$x01, 4+$x23, 4+$x45, 4+$x67,
+///           8, 9, 10, 11, 12+$x01, 12+$x23, 12+$x45, 12+$x67
+///       ]);
+///         };
+///     }
+/// }
+/// ```
+pub unsafe fn _mm256_shufflehi_epi16(a: __m256i, imm8: i32) -> __m256i {
+    let imm8 = (imm8 & 0xFF) as u8;
+    let a = a.as_i16x16();
+    macro_rules! shuffle_done {
+        ($x01:expr, $x23:expr, $x45:expr, $x67:expr) => {
+            #[cfg_attr(rustfmt, rustfmt_skip)]
+                         simd_shuffle16(a, a, [
+                             0, 1, 2, 3, 4+$x01, 4+$x23, 4+$x45, 4+$x67,
+                             8, 9, 10, 11, 12+$x01, 12+$x23, 12+$x45, 12+$x67
+                         ]);
+        };
+    }
+}

tests/target/issue-3105.rs

@@ -0,0 +1,30 @@
+// rustfmt-wrap_comments: true
+
+/// ```
+/// pub unsafe fn _mm256_shufflehi_epi16(a: __m256i, imm8: i32) -> __m256i {
+///     let imm8 = (imm8 & 0xFF) as u8;
+///     let a = a.as_i16x16();
+///     macro_rules! shuffle_done {
+///         ($x01:expr, $x23:expr, $x45:expr, $x67:expr) => {
+///             #[cfg_attr(rustfmt, rustfmt_skip)]
+///             simd_shuffle16(a, a, [
+///                 0, 1, 2, 3, 4+$x01, 4+$x23, 4+$x45, 4+$x67,
+///                 8, 9, 10, 11, 12+$x01, 12+$x23, 12+$x45, 12+$x67
+///             ]);
+///         };
+///     }
+/// }
+/// ```
+pub unsafe fn _mm256_shufflehi_epi16(a: __m256i, imm8: i32) -> __m256i {
+    let imm8 = (imm8 & 0xFF) as u8;
+    let a = a.as_i16x16();
+    macro_rules! shuffle_done {
+        ($x01:expr, $x23:expr, $x45:expr, $x67:expr) => {
+            #[cfg_attr(rustfmt, rustfmt_skip)]
+            simd_shuffle16(a, a, [
+                0, 1, 2, 3, 4+$x01, 4+$x23, 4+$x45, 4+$x67,
+                8, 9, 10, 11, 12+$x01, 12+$x23, 12+$x45, 12+$x67
+            ]);
+        };
+    }
+}