Skipping formatting of some configuration snippets

Author: davidalber

Configurations.md

@@ -1928,6 +1928,7 @@ lines are found, they are trimmed down to match this integer.
 Original Code:
 
 ```rust
+// rustfmt: skip
 fn foo() {
     println!("a");
 }
@@ -1985,6 +1986,7 @@ them, additional blank lines are inserted.
 Original Code (rustfmt will not change it with the default value of `0`):
 
 ```rust
+// rustfmt: skip
 fn foo() {
     println!("a");
 }

tests/system.rs

@@ -751,6 +751,16 @@ impl ConfigCodeBlock {
         loop {
             match ConfigurationSection::get_section(file) {
                 Some(ConfigurationSection::CodeBlock((block, start_line))) => {
+                    if block
+                        .split("\n")
+                        .take_while(|l| l.starts_with("//"))
+                        .map(|l| l == "// rustfmt: skip")
+                        .fold(false, |acc, b| acc || b)
+                    {
+                        // Pass over code blocks containing the skip directive.
+                        continue;
+                    }
+
                     code_block.set_code_block(block, start_line);
                     break;
                 }