Print numbers in a uniform way (#498)

* Print numbers in a uniform way

- Still preserve the radix (binary, octal, hexadecimal or decimal) used
  in the original source code.
- Still preserve scientific notation.
- Add 0 to fractions. `.1` -> `0.1`
- Remove trailing dots from integers. `1.` -> `1`
- Always print the radix letters lowercase. `0b`, `0o`, `0x`
- Always print scientific notation lowercase. `1e1`
- Always print hexadecimal digits uppercase. `0x123ABCDEF`
- Remove unneeded plus in scientific notation. `1e+1` -> `1e1`
- Remove unneeded zeroes in scientific notation. `1e-001` -> `1e-1`
- Preserve leading zeroes in non-decimal radix. This can be useful when
  working in binary, and having both `0b111000` and `0b000111` for
  example.

* Always print numbers lowercase

* Remove trailing dot in scientific notation

* Update snapshots

src/printer.js

@@ -729,13 +729,13 @@ function genericPrintNoParens(path, options, print) {
       return n.extra.raw;
     // Babel 6 Literal split
     case "NumericLiteral":
-      return n.extra.raw;
+      return printNumber(n.extra.raw);
     // Babel 6 Literal split
     case "BooleanLiteral":
     // Babel 6 Literal split
     case "StringLiteral":
     case "Literal":
-      if (typeof n.value === "number") return n.raw;
+      if (typeof n.value === "number") return printNumber(n.raw);
       if (typeof n.value !== "string") return "" + n.value;
 
       return nodeStr(n, options); // Babel 6
@@ -2523,6 +2523,16 @@ function makeString(rawContent, enclosingQuote) {
   return enclosingQuote + newContent + enclosingQuote;
 }
 
+function printNumber(rawNumber) {
+  return rawNumber.toLowerCase()
+    // Remove unnecessary plus and zeroes from scientific notation.
+    .replace(/^([\d.]+e)(?:\+|(-))?0*/, "$1$2")
+    // Make sure numbers always start with a digit.
+    .replace(/^\./, "0.")
+    // Remove trailing dot.
+    .replace(/\.(?=e|$)/, "");
+}
+
 function isFirstStatement(path) {
   const parent = path.getParentNode();
   const node = path.getValue();

tests/flow/unicode/__snapshots__/jsfmt.spec.js.snap

@@ -43,7 +43,7 @@ function utf16Length(str, pos) {
  * @return {boolean}      Whether code-unit is in a surrogate (hi/low) range
  */
 function inSurrogateRange(codeUnit) {
-  return 0xD800 <= codeUnit && codeUnit <= 0xDFFF;
+  return 0xd800 <= codeUnit && codeUnit <= 0xdfff;
 }
 
 /**

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

@@ -3,10 +3,116 @@ exports[`test number.js 1`] = `
 function test5(): string {
   return (100).toString();
 }
+
+0
+1
+
+0.1
+1.1
+
+.1
+1.
+
+0b1
+0B1
+0o1
+0O1
+0x1
+0X1
+
+0x123abcdef456ABCDEF
+0X123abcdef456ABCDEF
+0xdeadbeef;
+
+0b111000
+0b000111
+0B111000
+0B000111
+0o111000
+0o000111
+0O111000
+0O000111
+0x111000
+0x000111
+0X111000
+0X000111
+
+1e1
+1e+1
+1e-1
+1.e1
+.1e1
+1.1e1
+1.1e0010
+.1e+0010
+.1e-0010
+
+1E1
+1E+1
+1E-1
+1.E1
+.1E1
+1.1E1
+1.1E0010
+.1E+0010
+.1E-0010
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // parentheses around numeric literal should be preserved
 function test5(): string {
   return (100).toString();
 }
+
+0;
+1;
+
+0.1;
+1.1;
+
+0.1;
+1;
+
+0b1;
+0b1;
+0o1;
+0o1;
+0x1;
+0x1;
+
+0x123abcdef456abcdef;
+0x123abcdef456abcdef;
+0xdeadbeef;
+
+0b111000;
+0b000111;
+0b111000;
+0b000111;
+0o111000;
+0o000111;
+0o111000;
+0o000111;
+0x111000;
+0x000111;
+0x111000;
+0x000111;
+
+1e1;
+1e1;
+1e-1;
+1e1;
+0.1e1;
+1.1e1;
+1.1e10;
+0.1e10;
+0.1e-10;
+
+1e1;
+1e1;
+1e-1;
+1e1;
+0.1e1;
+1.1e1;
+1.1e10;
+0.1e10;
+0.1e-10;
 "
 `;

tests/literal/jsfmt.spec.js

@@ -1 +1,2 @@
-run_spec(__dirname);
+// flow-parser@0.38.0 fails to parse `1.e1`, so use babylon here.
+run_spec(__dirname, { parser: "babylon" });

tests/literal/number.js

@@ -2,3 +2,56 @@
 function test5(): string {
   return (100).toString();
 }
+
+0
+1
+
+0.1
+1.1
+
+.1
+1.
+
+0b1
+0B1
+0o1
+0O1
+0x1
+0X1
+
+0x123abcdef456ABCDEF
+0X123abcdef456ABCDEF
+0xdeadbeef;
+
+0b111000
+0b000111
+0B111000
+0B000111
+0o111000
+0o000111
+0O111000
+0O000111
+0x111000
+0x000111
+0X111000
+0X000111
+
+1e1
+1e+1
+1e-1
+1.e1
+.1e1
+1.1e1
+1.1e0010
+.1e+0010
+.1e-0010
+
+1E1
+1E+1
+1E-1
+1.E1
+.1E1
+1.1E1
+1.1E0010
+.1E+0010
+.1E-0010