Respect --file-lines when making various whitespace-related changes.

Various whitespace-related changes did not so far respect
`--file-lines`, see also [#5136](tests/target/issue-5136-4.rs). This PR
fixes this in all of the cases reported in #5136:

*  Newlines at the beginning of the file
*  Spaces at the beginning of the file
*  Missing newline at the end of the file
*  Space after a doc comment
*  Space before a comment in the last line of the file (without trailing
   newline)

The PR includes tests that fail without the fixes.

Author: martinboehme

src/formatting.rs

@@ -230,7 +230,14 @@ impl<'a, T: FormatHandler + 'a> FormatContext<'a, T> {
 
         // For some reason, the source_map does not include terminating
         // newlines so we must add one on for each file. This is sad.
-        source_file::append_newline(&mut visitor.buffer, self.config.style_edition());
+        let num_newlines = count_newlines(&visitor.buffer);
+        if self
+            .config
+            .file_lines()
+            .contains_line(&path, num_newlines + 1)
+        {
+            source_file::append_newline(&mut visitor.buffer, self.config.style_edition());
+        }
 
         format_lines(
             &mut visitor.buffer,

src/missed_spans.rs

@@ -63,7 +63,10 @@ impl<'a> FmtVisitor<'a> {
         let config = self.config;
         self.format_missing_inner(end, |this, last_snippet, snippet| {
             this.push_str(last_snippet.trim_end());
-            if last_snippet == snippet && !this.output_at_start() {
+            if last_snippet == snippet
+                && !this.output_at_start()
+                && !out_of_file_lines_range!(this, mk_sp(this.last_pos, end))
+            {
                 // No new lines in the snippet.
                 this.push_str("\n");
             }
@@ -100,7 +103,11 @@ impl<'a> FmtVisitor<'a> {
         let snippet = self.snippet(span);
 
         // Do nothing for spaces in the beginning of the file
-        if start == BytePos(0) && end.0 as usize == snippet.len() && snippet.trim().is_empty() {
+        if start == BytePos(0)
+            && end.0 as usize == snippet.len()
+            && snippet.trim().is_empty()
+            && !out_of_file_lines_range!(self, span)
+        {
             return;
         }
 
@@ -357,11 +364,20 @@ impl<'a> FmtVisitor<'a> {
             }
         }
 
-        let remaining = snippet[status.line_start..subslice.len() + offset].trim();
-        if !remaining.is_empty() {
-            self.push_str(&self.block_indent.to_string(self.config));
-            self.push_str(remaining);
-            status.line_start = subslice.len() + offset;
+        let mut remaining = &snippet[status.line_start..subslice.len() + offset];
+        status.line_start = subslice.len() + offset;
+
+        let skip_this_line = !self
+            .config
+            .file_lines()
+            .contains_line(file_name, status.cur_line);
+        if !skip_this_line {
+            remaining = remaining.trim();
+            if !remaining.is_empty() {
+                self.push_str(&self.block_indent.to_string(self.config));
+            }
         }
+
+        self.push_str(remaining);
     }
 }

src/visitor.rs

@@ -895,8 +895,12 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
             return false;
         }
 
-        let rewrite = attrs.rewrite(&self.get_context(), self.shape());
         let span = mk_sp(attrs[0].span.lo(), attrs[attrs.len() - 1].span.hi());
+        if out_of_file_lines_range!(self, span) {
+            return false;
+        }
+
+        let rewrite = attrs.rewrite(&self.get_context(), self.shape());
         self.push_rewrite(span, rewrite);
 
         false
@@ -1028,12 +1032,16 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
             .snippet_provider
             .opt_span_after(self.next_span(end_pos), "\n")
         {
+            let span = self.next_span(pos);
             if let Some(snippet) = self.opt_snippet(self.next_span(pos)) {
-                if snippet.trim().is_empty() {
-                    self.last_pos = pos;
-                } else {
+                if !snippet.trim().is_empty() {
+                    return;
+                }
+
+                if out_of_file_lines_range!(self, span) {
                     return;
                 }
+                self.last_pos = pos;
             }
         }
     }

tests/source/issue-5136-1.rs

@@ -0,0 +1,7 @@
+
+
+// Test that newlines at the top of this file are preserved when they're not
+// in the --file-lines range.
+
+// This should prevent rustfmt from many any formatting changes at all:
+// rustfmt-file_lines: []

tests/source/issue-5136-2.rs

@@ -0,0 +1,5 @@
+    use std;
+// Test that whitespace at beginning of file is preserved when not in
+// --file-lines range.
+// This should prevent rustfmt from making any formatting changes at all:
+// rustfmt-file_lines: []

tests/source/issue-5136-3.rs

@@ -0,0 +1,6 @@
+// rustfmt-file_lines: []
+// Test that a missing newline at the end of the file is preserved when the last
+// line is not in the --file-lines range.
+// Important: When editing this file, make sure not to add a newline at the end
+// of the last line.
+use std;

tests/source/issue-5136-4.rs

@@ -0,0 +1,4 @@
+// rustfmt-file_lines: []
+// Test that a missing space at the end of a doc comment is preserved when the
+// line is not in the --file-lines range.
+//! 

tests/source/issue-5136-5.rs

@@ -0,0 +1,6 @@
+// rustfmt-file_lines: []
+// Test that the space before the comment is not removed if the line is not
+// contained in `--file-lines`.
+// Note: It's important for the bug to repro that there is no newline at the
+// end of the comment
+fn f(){} // what

tests/target/issue-5136-1.rs

@@ -0,0 +1,7 @@
+
+
+// Test that newlines at the top of this file are preserved when they're not
+// in the --file-lines range.
+
+// This should prevent rustfmt from many any formatting changes at all:
+// rustfmt-file_lines: []

tests/target/issue-5136-2.rs

@@ -0,0 +1,5 @@
+    use std;
+// Test that whitespace at beginning of file is preserved when not in
+// --file-lines range.
+// This should prevent rustfmt from making any formatting changes at all:
+// rustfmt-file_lines: []