diff --git a/src/config.rs b/src/config.rs
index 3d41b51661e..357f99a6097 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -26,37 +26,56 @@ pub enum BlockIndentStyle {
 
 impl_enum_decodable!(BlockIndentStyle, Inherit, Tabbed, Visual);
 
-#[derive(RustcDecodable, Clone)]
-pub struct Config {
-    pub max_width: usize,
-    pub ideal_width: usize,
-    pub leeway: usize,
-    pub tab_spaces: usize,
-    pub newline_style: NewlineStyle,
-    pub fn_brace_style: BraceStyle,
-    pub fn_return_indent: ReturnIndent,
-    pub fn_args_paren_newline: bool,
-    pub struct_trailing_comma: SeparatorTactic,
-    pub struct_lit_trailing_comma: SeparatorTactic,
-    pub struct_lit_style: StructLitStyle,
-    pub enum_trailing_comma: bool,
-    pub report_todo: ReportTactic,
-    pub report_fixme: ReportTactic,
-    pub reorder_imports: bool, // Alphabetically, case sensitive.
-    pub expr_indent_style: BlockIndentStyle,
-}
+macro_rules! create_config {
+    ($($i:ident: $ty:ty),+ $(,)*) => (
+        #[derive(RustcDecodable, Clone)]
+        pub struct Config {
+            $(pub $i: $ty),+
+        }
 
-impl Config {
-    pub fn from_toml(toml: &str) -> Config {
-        let parsed = toml.parse().unwrap();
-        match toml::decode(parsed) {
-            Some(decoded) => decoded,
-            None => {
-                println!("Decoding config file failed. Config:\n{}", toml);
-                let parsed: toml::Value = toml.parse().unwrap();
-                println!("\n\nParsed:\n{:?}", parsed);
-                panic!();
+        impl Config {
+            pub fn from_toml(toml: &str) -> Config {
+                let parsed = toml.parse().unwrap();
+                match toml::decode(parsed) {
+                    Some(decoded) => decoded,
+                    None => {
+                        println!("Decoding config file failed. Config:\n{}", toml);
+                        let parsed: toml::Value = toml.parse().unwrap();
+                        println!("\n\nParsed:\n{:?}", parsed);
+                        panic!();
+                    }
+                }
+            }
+
+            pub fn override_value(&mut self, key: &str, val: &str) {
+                match key {
+                    $(
+                        stringify!($i) => {
+                            self.$i = val.parse::<$ty>().unwrap();
+                        }
+                    )+
+                    _ => panic!("Bad config key!")
+                }
             }
         }
-    }
+    )
+}
+
+create_config! {
+    max_width: usize,
+    ideal_width: usize,
+    leeway: usize,
+    tab_spaces: usize,
+    newline_style: NewlineStyle,
+    fn_brace_style: BraceStyle,
+    fn_return_indent: ReturnIndent,
+    fn_args_paren_newline: bool,
+    struct_trailing_comma: SeparatorTactic,
+    struct_lit_trailing_comma: SeparatorTactic,
+    struct_lit_style: StructLitStyle,
+    enum_trailing_comma: bool,
+    report_todo: ReportTactic,
+    report_fixme: ReportTactic,
+    reorder_imports: bool, // Alphabetically, case sensitive.
+    expr_indent_style: BlockIndentStyle,
 }
diff --git a/src/expr.rs b/src/expr.rs
index 1dfff001475..2fbdcb7d6c9 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -617,10 +617,8 @@ fn rewrite_binary_op(context: &RewriteContext,
     let operator_str = context.codemap.span_to_snippet(op.span).unwrap();
 
     // 1 = space between lhs expr and operator
-    let mut result =
-        try_opt!(lhs.rewrite(context,
-                             context.config.max_width - offset - 1 - operator_str.len(),
-                             offset));
+    let max_width = try_opt!(context.config.max_width.checked_sub(operator_str.len() + offset + 1));
+    let mut result = try_opt!(lhs.rewrite(context, max_width, offset));
 
     result.push(' ');
     result.push_str(&operator_str);
diff --git a/src/lib.rs b/src/lib.rs
index cc7111aae27..cd43be56a99 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -80,7 +80,7 @@ pub enum WriteMode {
     NewFile(&'static str),
     // Write the output to stdout.
     Display,
-    // Return the result as a mapping from filenames to StringBuffers.
+    // Return the result as a mapping from filenames to Strings.
     Return(&'static Fn(HashMap<String, String>)),
 }
 
diff --git a/src/utils.rs b/src/utils.rs
index 59f85b3ad27..a57ffb008ea 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -144,6 +144,19 @@ macro_rules! impl_enum_decodable {
                 }
             }
         }
+
+        impl ::std::str::FromStr for $e {
+            type Err = &'static str;
+
+            fn from_str(s: &str) -> Result<Self, Self::Err> {
+                match &*s {
+                    $(
+                        stringify!($x) => Ok($e::$x),
+                    )*
+                    _ => Err("Bad variant"),
+                }
+            }
+        }
     };
 }
 
diff --git a/tests/config/expr_visual_indent.toml b/tests/config/expr_visual_indent.toml
deleted file mode 100644
index 38a099e3bed..00000000000
--- a/tests/config/expr_visual_indent.toml
+++ /dev/null
@@ -1,16 +0,0 @@
-max_width = 100
-ideal_width = 80
-leeway = 5
-tab_spaces = 4
-newline_style = "Unix"
-fn_brace_style = "SameLineWhere"
-fn_return_indent = "WithArgs"
-fn_args_paren_newline = true
-struct_trailing_comma = "Vertical"
-struct_lit_style = "BlockIndent"
-struct_lit_trailing_comma = "Vertical"
-enum_trailing_comma = true
-report_todo = "Always"
-report_fixme = "Never"
-reorder_imports = false
-expr_indent_style = "Visual"
diff --git a/tests/config/reorder_imports.toml b/tests/config/reorder_imports.toml
deleted file mode 100644
index 5b1ce49a2f2..00000000000
--- a/tests/config/reorder_imports.toml
+++ /dev/null
@@ -1,16 +0,0 @@
-max_width = 100
-ideal_width = 80
-leeway = 5
-tab_spaces = 4
-newline_style = "Unix"
-fn_brace_style = "SameLineWhere"
-fn_return_indent = "WithArgs"
-fn_args_paren_newline = true
-struct_trailing_comma = "Vertical"
-struct_lit_trailing_comma = "Vertical"
-struct_lit_style = "BlockIndent"
-enum_trailing_comma = true
-report_todo = "Always"
-report_fixme = "Never"
-reorder_imports = true
-expr_indent_style = "Tabbed"
diff --git a/tests/config/visual_struct_lits.toml b/tests/config/visual_struct_lits.toml
deleted file mode 100644
index 61bf4b0aee5..00000000000
--- a/tests/config/visual_struct_lits.toml
+++ /dev/null
@@ -1,16 +0,0 @@
-max_width = 100
-ideal_width = 80
-leeway = 5
-tab_spaces = 4
-newline_style = "Unix"
-fn_brace_style = "SameLineWhere"
-fn_return_indent = "WithArgs"
-fn_args_paren_newline = true
-struct_trailing_comma = "Vertical"
-struct_lit_style = "VisualIndent"
-struct_lit_trailing_comma = "Vertical"
-enum_trailing_comma = true
-report_todo = "Always"
-report_fixme = "Never"
-reorder_imports = false
-expr_indent_style = "Tabbed"
diff --git a/tests/source/expr-visual-indent.rs b/tests/source/expr-visual-indent.rs
index c173d7bd7c4..3d7c1b92be8 100644
--- a/tests/source/expr-visual-indent.rs
+++ b/tests/source/expr-visual-indent.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: expr_visual_indent.toml
+// rustfmt-expr_indent_style: Visual
 
 // Visual level block indentation.
 
diff --git a/tests/source/imports-reorder.rs b/tests/source/imports-reorder.rs
index 2a90c212148..4feb8e90561 100644
--- a/tests/source/imports-reorder.rs
+++ b/tests/source/imports-reorder.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: reorder_imports.toml
+// rustfmt-reorder_imports: true
 
 use path::{C,/*A*/ A, B /* B */, self /* self */};
 
diff --git a/tests/source/struct_lits_visual.rs b/tests/source/struct_lits_visual.rs
index f14a56397ec..ea76a088a32 100644
--- a/tests/source/struct_lits_visual.rs
+++ b/tests/source/struct_lits_visual.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: visual_struct_lits.toml
+// rustfmt-struct_lit_style: VisualIndent
 
 // Struct literal expressions.
 
diff --git a/tests/system.rs b/tests/system.rs
index 19a68fc4b7b..3f63d224576 100644
--- a/tests/system.rs
+++ b/tests/system.rs
@@ -97,8 +97,16 @@ fn print_mismatches(result: HashMap<String, String>) {
 static HANDLE_RESULT: &'static Fn(HashMap<String, String>) = &handle_result;
 
 pub fn idempotent_check(filename: String) -> Result<(), HashMap<String, String>> {
-    let config = get_config(&filename);
+    let sig_comments = read_significant_comments(&filename);
+    let mut config = get_config(sig_comments.get("config").map(|x| &(*x)[..]));
     let args = vec!["rustfmt".to_owned(), filename];
+
+    for (key, val) in sig_comments {
+        if key != "target" && key != "config" {
+            config.override_value(&key, &val);
+        }
+    }
+
     // this thread is not used for concurrency, but rather to workaround the issue that the passed
     // function handle needs to have static lifetime. Instead of using a global RefCell, we use
     // panic to return a result in case of failure. This has the advantage of smoothing the road to
@@ -110,15 +118,15 @@ pub fn idempotent_check(filename: String) -> Result<(), HashMap<String, String>>
     )
 }
 
-// Reads test config file from comments and loads it
-fn get_config(file_name: &str) -> Box<Config> {
-    let config_file_name = read_significant_comment(file_name, "config")
-        .map(|file_name| {
-            let mut full_path = "tests/config/".to_owned();
-            full_path.push_str(&file_name);
-            full_path
-        })
-        .unwrap_or("default.toml".to_owned());
+
+// Reads test config file from comments and reads its contents.
+fn get_config(config_file: Option<&str>) -> Box<Config> {
+    let config_file_name = config_file.map(|file_name| {
+                                           let mut full_path = "tests/config/".to_owned();
+                                           full_path.push_str(&file_name);
+                                           full_path
+                                       })
+                                       .unwrap_or("default.toml".to_owned());
 
     let mut def_config_file = fs::File::open(config_file_name).ok().expect("Couldn't open config.");
     let mut def_config = String::new();
@@ -127,14 +135,16 @@ fn get_config(file_name: &str) -> Box<Config> {
     Box::new(Config::from_toml(&def_config))
 }
 
-fn read_significant_comment(file_name: &str, option: &str) -> Option<String> {
-    let file = fs::File::open(file_name).ok().expect("Couldn't read file for comment.");
+// Reads significant comments of the form: // rustfmt-key: value
+// into a hash map.
+fn read_significant_comments(file_name: &str) -> HashMap<String, String> {
+    let file = fs::File::open(file_name).ok().expect(&format!("Couldn't read file {}.", file_name));
     let reader = BufReader::new(file);
-    let pattern = format!("^\\s*//\\s*rustfmt-{}:\\s*(\\S+)", option);
+    let pattern = r"^\s*//\s*rustfmt-([^:]+):\s*(\S+)";
     let regex = regex::Regex::new(&pattern).ok().expect("Failed creating pattern 1.");
 
-    // matches exactly the lines containing significant comments or whitespace
-    let line_regex = regex::Regex::new(r"(^\s*$)|(^\s*//\s*rustfmt-[:alpha:]+:\s*\S+)")
+    // Matches lines containing significant comments or whitespace.
+    let line_regex = regex::Regex::new(r"(^\s*$)|(^\s*//\s*rustfmt-[^:]+:\s*\S+)")
         .ok().expect("Failed creating pattern 2.");
 
     reader.lines()
@@ -142,20 +152,26 @@ fn read_significant_comment(file_name: &str, option: &str) -> Option<String> {
           .take_while(|line| line_regex.is_match(&line))
           .filter_map(|line| {
               regex.captures_iter(&line).next().map(|capture| {
-                  capture.at(1).expect("Couldn't unwrap capture.").to_owned()
+                  (capture.at(1).expect("Couldn't unwrap capture.").to_owned(),
+                   capture.at(2).expect("Couldn't unwrap capture.").to_owned())
               })
           })
-          .next()
+          .collect()
 }
 
 // Compare output to input.
+// TODO: needs a better name, more explanation.
 fn handle_result(result: HashMap<String, String>) {
     let mut failures = HashMap::new();
 
     for (file_name, fmt_text) in result {
-        // If file is in tests/source, compare to file with same name in tests/target
-        let target_file_name = get_target(&file_name);
-        let mut f = fs::File::open(&target_file_name).ok().expect("Couldn't open target.");
+        // FIXME: reading significant comments again. Is there a way we can just
+        // pass the target to this function?
+        let sig_comments = read_significant_comments(&file_name);
+
+        // If file is in tests/source, compare to file with same name in tests/target.
+        let target = get_target(&file_name, sig_comments.get("target").map(|x| &(*x)[..]));
+        let mut f = fs::File::open(&target).ok().expect("Couldn't open target.");
 
         let mut text = String::new();
         // TODO: speedup by running through bytes iterator
@@ -171,15 +187,11 @@ fn handle_result(result: HashMap<String, String>) {
 }
 
 // Map source file paths to their target paths.
-fn get_target(file_name: &str) -> String {
+fn get_target(file_name: &str, target: Option<&str>) -> String {
     if file_name.starts_with("tests/source/") {
-        let target = read_significant_comment(file_name, "target");
-        let base = target.unwrap_or(file_name.trim_left_matches("tests/source/").to_owned());
+        let base = target.unwrap_or(file_name.trim_left_matches("tests/source/"));
 
-        let mut target_file = "tests/target/".to_owned();
-        target_file.push_str(&base);
-
-        target_file
+        format!("tests/target/{}", base)
     } else {
         file_name.to_owned()
     }
diff --git a/tests/target/expr-visual-indent.rs b/tests/target/expr-visual-indent.rs
index 3488e8c93c0..d74b5aae93c 100644
--- a/tests/target/expr-visual-indent.rs
+++ b/tests/target/expr-visual-indent.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: expr_visual_indent.toml
+// rustfmt-expr_indent_style: Visual
 
 // Visual level block indentation.
 
diff --git a/tests/target/imports-reorder.rs b/tests/target/imports-reorder.rs
index 27d394238e8..63ebbf1ec7b 100644
--- a/tests/target/imports-reorder.rs
+++ b/tests/target/imports-reorder.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: reorder_imports.toml
+// rustfmt-reorder_imports: true
 
 use path::{self /* self */, /* A */ A, B /* B */, C};
 
diff --git a/tests/target/struct_lits_visual.rs b/tests/target/struct_lits_visual.rs
index 248839cb869..bf73db5a815 100644
--- a/tests/target/struct_lits_visual.rs
+++ b/tests/target/struct_lits_visual.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: visual_struct_lits.toml
+// rustfmt-struct_lit_style: VisualIndent
 
 // Struct literal expressions.