[CS2] Fix v3 source map (#4671)

* Per discussion in #3075: if `sourceFiles` is unspecified, but `filename` is, use `filename`; output null instead of an empty string for `sources` or `sourceRoot`

* Update source map tests to reflect that now we return null instead of empty strings; check generated sources array

* Update source map documentation; still leave more obscure options undocumented

* Follow the TypeScript compiler’s example regarding v3SourceMap, but output empty strings instead of made-up filenames

* Have `sources` default to ‘<anonymous>’

Author: GeoffreyBooth

documentation/sections/nodejs_usage.md

@@ -20,6 +20,6 @@ The `compile` method has the signature `compile(code, options)` where `code` is
 
 * `options.sourceMap`, boolean: if true, a source map will be generated; and instead of returning a string, `compile` will return an object of the form `{js, v3SourceMap, sourceMap}`.
 * `options.inlineMap`, boolean: if true, output the source map as a base64-encoded string in a comment at the bottom.
-* `options.filename`, string: the filename to use for the source map.
+* `options.filename`, string: the filename to use for the source map. It can include a path (relative or absolute).
 * `options.bare`, boolean: if true, output without the [top-level function safety wrapper](#lexical-scope).
 * `options.header`, boolean: if true, output the `Generated by CoffeeScript` header.

lib/coffeescript/sourcemap.js

@@ -118,11 +118,18 @@ The starting column in the original source, relative to the previous column.
 
 Produce the canonical JSON object format for a "v3" source map.
 
+        sources = if options.sourceFiles
+          options.sourceFiles
+        else if options.filename
+          [options.filename]
+        else
+          ['<anonymous>']
+
         v3 =
           version:    3
           file:       options.generatedFile or ''
           sourceRoot: options.sourceRoot or ''
-          sources:    options.sourceFiles or ['']
+          sources:    sources
           names:      []
           mappings:   buffer
 

src/sourcemap.litcoffee

@@ -3,13 +3,13 @@ return if global.testingBrowser
 SourceMap = require '../src/sourcemap'
 
 vlqEncodedValues = [
-    [1, "C"],
-    [-1, "D"],
-    [2, "E"],
-    [-2, "F"],
-    [0, "A"],
-    [16, "gB"],
-    [948, "o7B"]
+    [1, 'C'],
+    [-1, 'D'],
+    [2, 'E'],
+    [-2, 'F'],
+    [0, 'A'],
+    [16, 'gB'],
+    [948, 'o7B']
 ]
 
 test "encodeVlq tests", ->
@@ -25,31 +25,41 @@ test "SourceMap tests", ->
   map.add [3, 0], [3, 4]
 
   testWithFilenames = map.generate {
-    sourceRoot: ""
-    sourceFiles: ["source.coffee"]
-    generatedFile: "source.js"
+    sourceRoot: ''
+    sourceFiles: ['source.coffee']
+    generatedFile: 'source.js'
   }
 
   deepEqual testWithFilenames, {
     version: 3
-    file: "source.js"
-    sourceRoot: ""
-    sources: ["source.coffee"]
+    file: 'source.js'
+    sourceRoot: ''
+    sources: ['source.coffee']
     names: []
-    mappings: "AAAA;;IACK,GAAC,CAAG;IAET"
+    mappings: 'AAAA;;IACK,GAAC,CAAG;IAET'
   }
 
   deepEqual map.generate(), {
     version: 3
-    file: ""
-    sourceRoot: ""
-    sources: [""]
+    file: ''
+    sourceRoot: ''
+    sources: ['<anonymous>']
     names: []
-    mappings: "AAAA;;IACK,GAAC,CAAG;IAET"
+    mappings: 'AAAA;;IACK,GAAC,CAAG;IAET'
   }
 
   # Look up a generated column - should get back the original source position.
   arrayEq map.sourceLocation([2,8]), [1,9]
 
   # Look up a point further along on the same line - should get back the same source position.
   arrayEq map.sourceLocation([2,10]), [1,9]
+
+test "#3075: v3 source map fields", ->
+  { js, v3SourceMap, sourceMap } = CoffeeScript.compile 'console.log Date.now()',
+    filename: 'tempus_fugit.coffee'
+    sourceMap: yes
+    sourceRoot: './www_root/coffee/'
+
+  v3SourceMap = JSON.parse v3SourceMap
+  arrayEq v3SourceMap.sources, ['tempus_fugit.coffee']
+  eq v3SourceMap.sourceRoot, './www_root/coffee/'

test/sourcemap.coffee

@@ -29,7 +29,7 @@ exports.eq = (a, b, msg) ->
   "Expected #{reset}#{a}#{red} to equal #{reset}#{b}#{red}"
 
 exports.arrayEq = (a, b, msg) ->
-  ok arrayEgal(a,b), msg or
+  ok arrayEgal(a, b), msg or
   "Expected #{reset}#{a}#{red} to deep equal #{reset}#{b}#{red}"
 
 exports.eqJS = (input, expectedOutput, msg) ->