This is the log output I got
18:11:39.268
Prepared asset index
18:11:39.300
Have 1346 total files to check or download
18:11:39.305
Waiting for 1346 futures
18:11:39.634
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/net/minecraftforge/forge/1.12.2-14.23.5.2838/forge-1.12.2-14.23.5.2838.jar
18:11:39.635
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\net\minecraftforge\forge\1.12.2-14.23.5.2838\forge-1.12.2-14.23.5.2838.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:39.759
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/com/typesafe/akka/akka-actor_2.11/2.3.3/akka-actor_2.11-2.3.3.jar
18:11:39.760
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\com\typesafe\akka\akka-actor_2.11\2.3.3\akka-actor_2.11-2.3.3.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:39.796
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-actors-migration_2.11/1.1.0/scala-actors-migration_2.11-1.1.0.jar
18:11:39.798
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-actors-migration_2.11\1.1.0\scala-actors-migration_2.11-1.1.0.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:39.808
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-compiler/2.11.1/scala-compiler-2.11.1.jar
18:11:39.809
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-compiler\2.11.1\scala-compiler-2.11.1.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:39.850
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/com/typesafe/config/1.2.1/config-1.2.1.jar
18:11:39.852
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\com\typesafe\config\1.2.1\config-1.2.1.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:39.900
Couldn't fetch SHA1 checksum for https://s3.amazonaws.com/Minecraft.Download/versions/1.12.2/1.12.2.jar
18:11:39.902
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\versions\1.12.2\1.12.2.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:39.967
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/plugins/scala-continuations-library_2.11/1.0.2/scala-continuations-library_2.11-1.0.2.jar
18:11:39.968
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\plugins\scala-continuations-
18:11:40.051
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/plugins/scala-continuations-plugin_2.11.1/1.0.2/scala-continuations-plugin_2.11.1-1.0.2.jar
18:11:40.052
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\plugins\scala-continuations-plugin_2.11.1\1.0.2\scala-continuations-plugin_2.11.1-1.0.2.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:40.059
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-library/2.11.1/scala-library-2.11.1.jar
18:11:40.061
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-library\2.11.1\scala-library-2.11.1.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:40.075
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-parser-combinators_2.11/1.0.1/scala-parser-combinators_2.11-1.0.1.jar
18:11:40.077
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-parser-combinators_2.11\1.0.1\scala-parser-combinators_2.11-1.0.1.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:40.101
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-reflect/2.11.1/scala-reflect-2.11.1.jar
18:11:40.102
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-reflect\2.11.1\scala-reflect-2.11.1.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:40.175
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-swing_2.11/1.0.1/scala-swing_2.11-1.0.1.jar
18:11:40.175
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-swing_2.11\1.0.1\scala-swing_2.11-1.0.1.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:40.233
Couldn't fetch SHA1 checksum for http://files.minecraftforge.net/maven/org/scala-lang/scala-xml_2.11/1.0.2/scala-xml_2.11-1.0.2.jar
18:11:40.235
Have local file C:\Users\Santiago\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-xml_2.11\1.0.2\scala-xml_2.11-1.0.2.jar but don't know what size or hash it should be. Have to assume it's good.
18:11:40.763
Nothing to download!
18:11:40.763
Extracting 3 files!
18:11:40.837
Version does not support log configuration, will assume one plaintext entry per line
18:11:40.837
Installing versions!
18:11:50.282
Process crashed with exit code 1