I was launching Minecraft for the first time on my new computer, a MacBook Pro. But I got error messages from the launcher and was told to report this to this website.

By the way, after this error message appeared, the button where PLAY should be became gray, with LAUNCHING... on it and was not able to be use. The game could not be operated.

Here is the bug info I received from the launcher :
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[18:37:06 WARN]: No assets index file /Users/Tacoco/Library/Application Support/minecraft/assets/virtual/1.8; can't reconstruct assets
[18:37:06 INFO]: Launching in /Users/Tacoco/Library/Application Support/minecraft
[18:37:06 FATAL]: Fatal error launching game. Report this to http://bugs.mojang.com please!
java.io.FileNotFoundException: File '/Users/Tacoco/Library/Application Support/minecraft/assets/indexes/1.8.json' does not exist
at org.apache.commons.io.FileUtils.openInputStream(FileUtils.java:299) ~[launcher.jar:1.6.48]
at org.apache.commons.io.FileUtils.readFileToString(FileUtils.java:1711) ~[launcher.jar:1.6.48]
at net.minecraft.launcher.game.MinecraftGameRunner.getAssetObject(MinecraftGameRunner.java:244) ~[launcher.jar:1.6.48]
at net.minecraft.launcher.game.MinecraftGameRunner.launchGame(MinecraftGameRunner.java:156) ~[launcher.jar:1.6.48]
at com.mojang.launcher.game.runner.AbstractGameRunner.onDownloadJobFinished(AbstractGameRunner.java:186) [launcher.jar:1.6.48]
at com.mojang.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:122) [launcher.jar:1.6.48]
at acom.mojang.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher.jar:1.6.48]
at com.mojang.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:86) [launcher.jar:1.6.48]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_60]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_60]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_60]
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Beside this log, I also found that a new tag-page was opened automatically, namely Game Output, but no content was in the page.

I have searched this web-site, but did not found any resolution for "1.8.json".
Could any one kindly teach me how to solve this problem, please?

Thank you very much.