JSX maintains spaces that matter (fixes #30 and thus part of #73)

src/printer.js

@@ -2034,7 +2034,7 @@ function printJSXElement(path, options, print) {
 
             children.push(
               beginBreak ? hardline : "",
-              child.value.replace(/^\s+|\s+$/g, ""),
+              child.value.replace(/^\s+|\s+$/g, endBreak ? "" : " "),
               endBreak ? hardline : ""
             );
           } else if (/\n/.test(child.value)) {

tests/prettier/__snapshots__/jsfmt.spec.js.snap

@@ -73,13 +73,24 @@ const comp4 = (
   <div
     style={styles}
     key=\"something\"
-  >Create wrapping parens and indent<strong>all the things</strong>.</div>
+  >Create wrapping parens and indent <strong>all the things</strong>.</div>
 );
 
 const comp5 = <div>Keep it on one line.</div>;
 "
 `;
 
+exports[`test jsx-significant-space.js 1`] = `
+"<span>
+    foo <span>bar</span>
+</span>
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+<span>
+   foo <span>bar</span>
+</span>;
+"
+`;
+
 exports[`test jsx-split-attrs.js 1`] = `
 "long_closed =
   <BaseForm url=\"/auth/google\" method=\"GET\" colour=\"blue\" size=\"large\" submitLabel=\"Sign in with Google\"/>
@@ -168,7 +179,7 @@ const render4 = ({ styles }) => (
   <div
     style={styles}
     key=\"something\"
-  >Create wrapping parens and indent<strong>all the things</strong>.</div>
+  >Create wrapping parens and indent <strong>all the things</strong>.</div>
 );
 
 const render5 = ({ styles }) => <div>Keep it on one line.</div>;

tests/prettier/jsx-significant-space.js

@@ -0,0 +1,3 @@
+<span>
+    foo <span>bar</span>
+</span>