I wanted to learn how to make mods. My help was youtube video from TurtyWurty channel. I made everything, and when i tried to start the game, this appeared:

2020-05-15 21:23:05,465 main WARN Advanced terminal features are not available in this environment
�[1;31m[21:23:06] [Render thread/ERROR] [minecraft/ResourceIndex]: Can't find the resource index file: assets\indexes\1.15.json
�[m�[32m[21:23:06] [Render thread/INFO] [minecraft/Minecraft]: Setting user: Player533
�[m�[32m[21:23:12] [Render thread/INFO] [minecraft/Minecraft]: Backend library: LWJGL version 3.2.2 build 10
�[m---- Minecraft Crash Report ----
// I'm sorry, Dave.

Time: 15.05.20 21:23
Description: Initializing game

java.lang.NullPointerException: Initializing game
    at net.minecraftforge.fml.loading.progress.EarlyProgressVisualization.join(EarlyProgressVisualization.java:40) ~[forge-1.15.2-31.1.0_mapped_snapshot_20190719-1.14.3-launcher.jar:?] {}
    at net.minecraft.client.Minecraft.<init>(Minecraft.java:371) [forge-1.15.2-31.1.0_mapped_snapshot_20190719-1.14.3.jar:?] {}
    at net.minecraft.client.main.Main.main(SourceFile:166) [forge-1.15.2-31.1.0_mapped_snapshot_20190719-1.14.3.jar:?] {}
    at mcp.client.Start.main(Start.java:17) [forge-1.15.2-31.1.0_mapped_snapshot_20190719-1.14.3.jar:?] {}


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Render thread
Stacktrace:
    at net.minecraftforge.fml.loading.progress.EarlyProgressVisualization.join(EarlyProgressVisualization.java:40)
    at net.minecraft.client.Minecraft.<init>(Minecraft.java:371)

-- Initialization --
Details:
Stacktrace:
    at net.minecraft.client.main.Main.main(SourceFile:166)
    at mcp.client.Start.main(Start.java:17)

-- System Details --
Details:
    Minecraft Version: 1.15.2
    Minecraft Version ID: 1.15.2
    Operating System: Windows 7 (amd64) version 6.1
    Java Version: 1.8.0_251, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 503656368 bytes (480 MB) / 682622976 bytes (651 MB) up to 1418723328 bytes (1353 MB)
    CPUs: 4
    JVM Flags: 0 total; 
    Launched Version: mcp
    Backend library: LWJGL version 3.2.2 build 10
    Backend API: NO CONTEXT
    GL Caps: 
    Using VBOs: Yes
    Is Modded: Definitely; Client brand changed to 'forge'
    Type: Client (map_client.txt)
    CPU: <unknown>
#@!@# Game crashed! Crash report saved to: #@!@# C:\Users\USER PC\Desktop\apocaliptica\.\crash-reports\crash-2020-05-15_21.23.12-client.txt

 

I tried to run game without any changes in file, clear mdk files. Effect was same. I'm using eclipse, mdk 1.15.2 31.1.0 and java is jdk 1.8.0_251. I hope someone can help me  with this...
 

 

You shouldn't be using the mcp.client.Start as your main class. You should be using net.minecraftforge.userdev.LaunchTesting instead.
Or as diesieben said, let forge generate them for you.

Edited May 15, 20205 yr by Vinyarion

Mixing both answers helped, after genEclipseRuns, net.minecraftforge.userdev.LaunchTesting showed. Thanks.