Contributing guidelines

• I've read the contributing guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

When given the expected parameters, a collection as first parameter and a value as second, index function should return the corresponding index (number), if the value is present in the collection?! Instead it raises an error (...)Call to function "index" failed: key for tuple must be number.(...) (presumably because of collection.go of go-cty)

index is in fact behaving exactly as the element function. What's the purpose of an index function expecting a number (aka the searched index itself) = why search for something you already know?!!!

Expected behaviour

Knowing the differences between element and index functions (per hcl docs and/or based on comments in collection.go and the corresponding functions mapped from go-cty):

element(list, index)

• element retrieves a single element from a list (prefer the built-in index syntax list[index]).
• The index is zero-based. This function produces an error if used with an empty list.

index(list, value)

• index should find the element index for a given value in a list.
• The returned index is zero-based.
• This function should produce an error if the given value is not present in the list.

With bug.hcl (aka dummy config ... just for demonstration / nothing specifically related to annotations = same error no matter where you use index function):

target "bug" {
  annotations = [
    "foo=${element(["a", "b", "c"], 1)}",  // Work as expected/documented = returns "b"
    "bar=${index(["a", "b", "c"], "b")}",  // Raise an error !!! Should return 1
    // "baz=${index(["a", "b", "c"], 1)}", // NOK = same behavior as "element" function = if you already know the index ... what's the purpose of this function ?!!!
  ]
}

Expected:

$ docker buildx bake --file path/to/bug.hcl --print bug
[+] Building 0.0s (1/1) FINISHED
 => [internal] load local bake definitions                                   0.0s
 => => reading path/to/bug.hcl 479B / 479B                                   0.0s
{
  "group": {
    "default": {
      "targets": [
        "bug"
      ]
    }
  },
  "target": {
    "bug": {
      "annotations": [
        "foo=b",
        "bar=1"
      ],
      "context": ".",
      "dockerfile": "Dockerfile"
    }
  }
}

Actual behaviour

Raise an error with the same/previous bug.hcl:

$ docker buildx bake --file path/to/bug.hcl --print bug
[+] Building 0.0s (1/1) FINISHED
 => [internal] load local bake definitions                                   0.0s
 => => reading path/to/bug.hcl 479B / 479B                                   0.0s
path/to/bug.hcl:4
--------------------
   2 |       annotations = [
   3 |         "foo=${element(["a", "b", "c"], 1)}",  // Work as expected/documented = returns "b"
   4 | >>>     "bar=${index(["a", "b", "c"], "b")}",  // Raise an error !!! Should return 1
   5 |         // "baz=${index(["a", "b", "c"], 1)}", // NOK = same behavior as "element" function = if you already know the index ... what's the purpose of this function ?!!!
   6 |       ]
--------------------
ERROR: path/to/bug.hcl:4,12-18: Error in function call; Call to function "index" failed: key for tuple must be number., and 1 other diagnostic(s)

Buildx version

github.com/docker/buildx v0.13.1 7884339

Docker info

Client: Docker Engine - Community
 Version:    26.0.0
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.13.1
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.4.1
    Path:     /usr/local/lib/docker/cli-plugins/docker-compose
  scan: Docker Scan (Docker Inc.)
    Version:  v0.23.0
    Path:     /usr/libexec/docker/cli-plugins/docker-scan

Server:
 Containers: 1
  Running: 0
  Paused: 0
  Stopped: 1
 Images: 2
 Server Version: 26.0.0
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: ae07eda36dd25f8a1b98dfbf587313b99c0190bb
 runc version: v1.1.12-0-g51d5e94
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 6.5.0-26-generic
 Operating System: Ubuntu 22.04.4 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: ...
 Total Memory: ...
 Name: ...
 ID: ...
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Builders list

NAME/NODE     DRIVER/ENDPOINT   STATUS    BUILDKIT   PLATFORMS
default*      docker                                 
 \_ default    \_ default       running   v0.13.1    linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/386

Configuration

target "bug" {
  annotations = [
    "foo=${element(["a", "b", "c"], 1)}",  // Work as expected/documented = returns "b"
    "bar=${index(["a", "b", "c"], "b")}",  // Raise an error !!! Should return 1
    // "baz=${index(["a", "b", "c"], 1)}", // NOK = same behavior as "element" function = if you already know the index ... what's the purpose of this function ?!!!
  ]
}

Build logs

No response

Additional info

First things first: bake feature is great 😍 Thanks for that 🙇

Since index is such a fundamental function, not having found an issue about it (and seen others not bothering/using it as/instead of element), I doubted myself for a while before filling this bug (not being fluent in Go, I stopped when digging deeper in go-cty sources became needed).

I don't know if it's related to how you're mapping go-cty in your hcl parser or the library itself ... but we should expect index or at least a function (no matter how it's named ... it should have a different behavior than the one expected from element ... the features subset being limited, may I say duplicates should not be expected?!) returning an index (as a number) ... not already known (the expected result shouldn't be provided as one of its parameters 🤐🤷)

Hope it can be fixed easily.

Thanks for everything.