path: make format() consistent and more functional

Make the win32 and posix versions of path.format() consistent in when
they add a directory separator between the dir and base parts of the
path (always add it unless the dir part is the same as the root).

Also, path.format() is now more functional in that it uses the name
and ext parts of the path if the base part is left out and it uses
the root part if the dir part is left out.

doc/api/path.markdown

@@ -95,6 +95,16 @@ Returns a path string from an object, the opposite of `path.parse` above.
     // returns
     '/home/user/dir/file.txt'
 
+    // `root` will be used if `dir` is not specified and `name` + `ext` will be used
+    // if `base` is not specified
+    path.format({
+        root : "/",
+        ext : ".txt",
+        name : "file"
+    })
+    // returns
+    '/file.txt'
+
 ## path.isAbsolute(path)
 
 Determines whether `path` is an absolute path. An absolute path will always

lib/path.js

@@ -361,21 +361,13 @@ win32.format = function(pathObject) {
     );
   }
 
-  var root = pathObject.root || '';
-
-  if (typeof root !== 'string') {
-    throw new TypeError(
-        '"pathObject.root" must be a string or undefined, not ' +
-        typeof pathObject.root
-    );
-  }
-
-  var dir = pathObject.dir;
-  var base = pathObject.base || '';
+  var dir = pathObject.dir || pathObject.root;
+  var base = pathObject.base ||
+    ((pathObject.name || '') + (pathObject.ext || ''));
   if (!dir) {
     return base;
   }
-  if (dir[dir.length - 1] === win32.sep) {
+  if (dir === pathObject.root) {
     return dir + base;
   }
   return dir + win32.sep + base;
@@ -570,18 +562,16 @@ posix.format = function(pathObject) {
     );
   }
 
-  var root = pathObject.root || '';
-
-  if (typeof root !== 'string') {
-    throw new TypeError(
-        '"pathObject.root" must be a string or undefined, not ' +
-        typeof pathObject.root
-    );
+  var dir = pathObject.dir || pathObject.root;
+  var base = pathObject.base ||
+    ((pathObject.name || '') + (pathObject.ext || ''));
+  if (!dir) {
+    return base;
   }
-
-  var dir = pathObject.dir ? pathObject.dir + posix.sep : '';
-  var base = pathObject.base || '';
-  return dir + base;
+  if (dir === pathObject.root) {
+    return dir + base;
+  }
+  return dir + posix.sep + base;
 };
 
 

test/parallel/test-path-parse-format.js

@@ -1,15 +1,16 @@
 'use strict';
 require('../common');
-var assert = require('assert');
-var path = require('path');
+const assert = require('assert');
+const path = require('path');
 
-var winPaths = [
+const winPaths = [
   'C:\\path\\dir\\index.html',
-  'C:\\another_path\\DIR\\1\\2\\33\\index',
+  'C:\\another_path\\DIR\\1\\2\\33\\\\index',
   'another_path\\DIR with spaces\\1\\2\\33\\index',
   '\\foo\\C:',
   'file',
   '.\\file',
+  'C:\\',
   '',
 
   // unc
@@ -19,13 +20,17 @@ var winPaths = [
   '\\\\?\\UNC\\server\\share'
 ];
 
-var winSpecialCaseFormatTests = [
+const winSpecialCaseFormatTests = [
   [{dir: 'some\\dir'}, 'some\\dir\\'],
   [{base: 'index.html'}, 'index.html'],
+  [{root: 'C:\\'}, 'C:\\'],
+  [{name: 'index', ext: '.html'}, 'index.html'],
+  [{dir: 'some\\dir', name: 'index', ext: '.html'}, 'some\\dir\\index.html'],
+  [{root: 'C:\\', name: 'index', ext: '.html'}, 'C:\\index.html'],
   [{}, '']
 ];
 
-var unixPaths = [
+const unixPaths = [
   '/home/user/dir/file.txt',
   '/home/user/a dir/another File.zip',
   '/home/user/a dir//another&File.',
@@ -35,16 +40,21 @@ var unixPaths = [
   '.\\file',
   './file',
   'C:\\foo',
+  '/',
   ''
 ];
 
-var unixSpecialCaseFormatTests = [
+const unixSpecialCaseFormatTests = [
   [{dir: 'some/dir'}, 'some/dir/'],
   [{base: 'index.html'}, 'index.html'],
+  [{root: '/'}, '/'],
+  [{name: 'index', ext: '.html'}, 'index.html'],
+  [{dir: 'some/dir', name: 'index', ext: '.html'}, 'some/dir/index.html'],
+  [{root: '/', name: 'index', ext: '.html'}, '/index.html'],
   [{}, '']
 ];
 
-var errors = [
+const errors = [
   {method: 'parse', input: [null],
    message: /Path must be a string. Received null/},
   {method: 'parse', input: [{}],
@@ -63,10 +73,6 @@ var errors = [
    message: /Parameter "pathObject" must be an object, not boolean/},
   {method: 'format', input: [1],
    message: /Parameter "pathObject" must be an object, not number/},
-  {method: 'format', input: [{root: true}],
-   message: /"pathObject\.root" must be a string or undefined, not boolean/},
-  {method: 'format', input: [{root: 12}],
-   message: /"pathObject\.root" must be a string or undefined, not number/},
 ];
 
 checkParseFormat(path.win32, winPaths);