Add some tests for hard tab mode.

tests/source/hard-tabs.rs

@@ -0,0 +1,69 @@
+// rustfmt-hard_tabs: true
+
+fn main() {
+let x = Bar;
+
+let y = Foo {a: x };
+
+Foo { a: foo() /* comment*/, /* comment*/ b: bar(), ..something };
+
+fn foo(a: i32, a: i32, a: i32, a: i32, a: i32, a: i32, a: i32, a: i32, a: i32, a: i32, a: i32) {}
+
+let str = "AAAAAAAAAAAAAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAaAa";
+
+if let (some_very_large, tuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuple) = 1
++ 2 + 3 {
+}
+
+    if cond() {
+        something();
+    } else  if different_cond() {
+        something_else();
+    } else {
+        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa + aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+    }
+    
+unsafe /* very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong comment */ {}
+
+unsafe // So this is a very long comment.
+   // Multi-line, too.
+   // Will it still format correctly?
+{
+}
+
+let z = [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx, yyyyyyyyyyyyyyyyyyyyyyyyyyy, zzzzzzzzzzzzzzzzzz, q];
+
+fn generic<T>(arg: T) -> &SomeType
+    where T: Fn(// First arg
+        A,
+        // Second argument
+        B, C, D, /* pre comment */ E /* last comment */) -> &SomeType {
+    arg(a, b, c, d, e)    
+}
+
+    loong_func().quux(move || {
+        if true {
+            1
+        } else {
+            2
+        }
+    });
+
+    fffffffffffffffffffffffffffffffffff(a,
+                                        {
+                                            SCRIPT_TASK_ROOT
+                                            .with(|root| {
+                                                *root.borrow_mut()  =   Some(&script_task);
+                                            });
+                                        });
+    a.b
+     .c
+     .d();
+    
+    x().y(|| {
+        match cond() {
+            true => (),
+            false => (),
+        }
+    });
+}

tests/target/hard-tabs.rs

@@ -0,0 +1,95 @@
+// rustfmt-hard_tabs: true
+
+fn main() {
+	let x = Bar;
+
+	let y = Foo { a: x };
+
+	Foo {
+		a: foo(), // comment
+		// comment
+		b: bar(),
+		..something
+	};
+
+	fn foo(a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32,
+	       a: i32) {
+	}
+
+	let str = "AAAAAAAAAAAAAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAaAAAAAAAAAAAAAAAAAAAAA\
+	           AAAAAAAAAAAAaAa";
+
+	if let (some_very_large, tuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuple) =
+	       1 + 2 + 3 {
+	}
+
+	if cond() {
+		something();
+	} else if different_cond() {
+		something_else();
+	} else {
+		aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa +
+		aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+	}
+
+	unsafe /* very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong
+	        * comment */ {
+	}
+
+	unsafe /* So this is a very long comment.
+	        * Multi-line, too.
+	        * Will it still format correctly? */ {
+	}
+
+	let z = [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx,
+	         yyyyyyyyyyyyyyyyyyyyyyyyyyy,
+	         zzzzzzzzzzzzzzzzzz,
+	         q];
+
+	fn generic<T>(arg: T) -> &SomeType
+		where T: Fn(// First arg
+		            A,
+		            // Second argument
+		            B,
+		            C,
+		            D,
+		            // pre comment
+		            E /* last comment */) -> &SomeType
+	{
+		arg(a, b, c, d, e)
+	}
+
+	loong_func().quux(move || {
+		if true {
+			1
+		} else {
+			2
+		}
+	});
+
+	fffffffffffffffffffffffffffffffffff(a,
+	                                    {
+		                                    SCRIPT_TASK_ROOT.with(|root| {
+			                                    *root.borrow_mut() = Some(&script_task);
+		                                    });
+	                                    });
+	a.b
+	 .c
+	 .d();
+
+	x().y(|| {
+		match cond() {
+			true => (),
+			false => (),
+		}
+	});
+}