Change assertion API to pass error to callback

Don’t assume anything about metadata. Just give assertion callers access
to the error object.

Signed-off-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

spec/atom-spec.coffee

@@ -127,7 +127,7 @@ describe "the `atom` global", ->
           column: 3
           originalError: error
 
-  describe ".assert(condition, message, metadata)", ->
+  describe ".assert(condition, message, callback)", ->
     errors = null
 
     beforeEach ->
@@ -142,17 +142,11 @@ describe "the `atom` global", ->
         expect(errors[0].message).toBe "Assertion failed: a == b"
         expect(errors[0].stack).toContain('atom-spec')
 
-      describe "if metadata is an object", ->
-        it "assigns the object on the error as `metadata`", ->
-          metadata = {foo: 'bar'}
-          atom.assert(false, "a == b", metadata)
-          expect(errors[0].metadata).toBe metadata
-
-      describe "if metadata is a function", ->
-        it "assigns the function's return value on the error as `metadata`", ->
-          metadata = {foo: 'bar'}
-          atom.assert(false, "a == b", -> metadata)
-          expect(errors[0].metadata).toBe metadata
+      describe "if passed a callback function", ->
+        it "calls the callback with the assertion failure's error object", ->
+          error = null
+          atom.assert(false, "a == b", (e) -> error = e)
+          expect(error).toBe errors[0]
 
     describe "if the condition is true", ->
       it "does nothing", ->

src/atom.coffee

@@ -721,17 +721,12 @@ class Atom extends Model
   Section: Private
   ###
 
-  assert: (condition, message, metadata) ->
+  assert: (condition, message, callback) ->
     return true if condition
 
     error = new Error("Assertion failed: #{message}")
     Error.captureStackTrace(error, @assert)
-
-    if metadata?
-      if typeof metadata is 'function'
-        error.metadata = metadata()
-      else
-        error.metadata = metadata
+    callback?(error)
 
     @emitter.emit 'did-fail-assertion', error
 

src/tokenized-buffer.coffee

@@ -296,10 +296,12 @@ class TokenizedBuffer extends Model
     # undefined. This should paper over the problem but we want to figure out
     # what is happening:
     tokenizedLine = @tokenizedLineForRow(row)
-    atom.assert tokenizedLine?, "TokenizedLine is defined", =>
-      metadata:
+    atom.assert tokenizedLine?, "TokenizedLine is defined", (error) =>
+      error.metadata = {
         row: row
         rowCount: @tokenizedLines.length
+      }
+
     return false unless tokenizedLine?
 
     return false if @buffer.isRowBlank(row) or tokenizedLine.isComment()