Panic: index out of range when stage alias has the same name as base image

[DGollings]

Actual behavior
A clear and concise description of what the bug is.

Kaniko panics with an index out of range when I think a image and alias are duplicates of each other. For example FROM composer AS composer

Removing AS composer fixed it

Output

INFO[0000] Resolved base name composer to composer      
INFO[0000] Resolved base name php:7.1-apache to php:7.1-apache 
INFO[0000] Resolved base name composer to composer      
INFO[0000] Resolved base name php:7.1-apache to php:7.1-apache 
panic: runtime error: index out of range

goroutine 1 [running]:
github.com/GoogleContainerTools/kaniko/pkg/executor.CalculateDependencies(0x3082680, 0x2, 0x2, 0x3082680)
	/go/src/github.com/GoogleContainerTools/kaniko/pkg/executor/build.go:442 +0xf12
github.com/GoogleContainerTools/kaniko/pkg/executor.DoBuild(0x3082680, 0x1, 0x0, 0x0, 0xc000624820)
	/go/src/github.com/GoogleContainerTools/kaniko/pkg/executor/build.go:510 +0x1ca
github.com/GoogleContainerTools/kaniko/cmd/executor/cmd.glob..func2(0x3071a40, 0xc0005356e0, 0x0, 0x6)
	/go/src/github.com/GoogleContainerTools/kaniko/cmd/executor/cmd/root.go:95 +0x11b
github.com/spf13/cobra.(*Command).execute(0x3071a40, 0xc00003a080, 0x6, 0x6, 0x3071a40, 0xc00003a080)

	/go/src/github.com/GoogleContainerTools/kaniko/vendor/github.com/spf13/cobra/command.go:766 +0x2ae
github.com/spf13/cobra.(*Command).ExecuteC(0x3071a40, 0x18063cd, 0xc0004fff88, 0xc000046178)
	/go/src/github.com/GoogleContainerTools/kaniko/vendor/github.com/spf13/cobra/command.go:852 +0x2ec
github.com/spf13/cobra.(*Command).Execute(...)
	/go/src/github.com/GoogleContainerTools/kaniko/vendor/github.com/spf13/cobra/command.go:800
main.main()
	/go/src/github.com/GoogleContainerTools/kaniko/cmd/executor/main.go:26 +0x2e

Expected behavior
A clear and concise description of what you expected to happen.

Not crash

To Reproduce
Steps to reproduce the behavior:

1. Create a dockerfile with the image and alias name being identical (ignoring why you would ever do this)
2. Try and build it

Additional Information

• Dockerfile
  FROM composer AS composer
  # rest doesnt matter

• Kaniko Image (fully qualified with digest)
  Didn't specify, I assume latest as of 2019-12-25
  gcr.io/kaniko-project/executor:debug

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing	- [no]
Please check if the build works in docker but not in kaniko	- [yes]
Please check if this error is seen when you use --cache flag	- [n/a]
Please check if your dockerfile is a multistage dockerfile	- [yes]

[MyIgel]

Alternatively: change it to FROM composer:latest AS composer

[mickvangelderen]

Reproduction on v1.23.2:

echo -e 'FROM scratch AS scratch' > Dockerfile | tar -cf - Dockerfile | gzip -9 | docker run \
  --interactive -v $(pwd):/workspace gcr.io/kaniko-project/executor:v1.23.2 \
  --context tar://stdin \
  --no-push

Emits:

INFO[0000] To simulate EOF and exit, press 'Ctrl+D'     
INFO[0000] Resolved base name scratch to scratch        
panic: runtime error: index out of range [0] with length 0

goroutine 1 [running, locked to thread]:
github.com/GoogleContainerTools/kaniko/pkg/executor.CalculateDependencies({0xc0004260b0, 0x1, 0xc0003c3878?}, 0x2806b80, 0xc000796270)
	/src/pkg/executor/build.go:637 +0xc7a
github.com/GoogleContainerTools/kaniko/pkg/executor.DoBuild(0x2806b80)
	/src/pkg/executor/build.go:717 +0x225
github.com/GoogleContainerTools/kaniko/cmd/executor/cmd.init.func2(0xc00050ea00?, {0x196b03d?, 0x4?, 0x196b041?})
	/src/cmd/executor/cmd/root.go:190 +0x1b1
github.com/spf13/cobra.(*Command).execute(0x27f2540, {0xc000144050, 0x3, 0x3})
	/src/vendor/github.com/spf13/cobra/command.go:989 +0xab1
github.com/spf13/cobra.(*Command).ExecuteC(0x27f2540)
	/src/vendor/github.com/spf13/cobra/command.go:1117 +0x3ff
github.com/spf13/cobra.(*Command).Execute(0x197683e?)
	/src/vendor/github.com/spf13/cobra/command.go:1041 +0x13
main.main()
	/src/cmd/executor/main.go:31 +0x65

Array access

Maybe baseImageIndex should not be able to resolve to itself. Currently it can return the current stage index, but it should maybe already stop when i >= currentStage instead of i > currentStage.

[mickvangelderen]

I created #3245 with this 1 character change.