Recognize Dockerfile.*

[chrisdoherty4]

I'm using vscode-docker v1.1.0 with VSCode 1.44.2 and it doesn't seem to recognise Dockerfile.* files. An issue was raised at microsoft/vscode#38797 (albeit years ago) suggesting it is a feature so I think this is either a bug or there is some setting I haven't found yet that needs turning on?

[bwateratmsft]

At present this is intentional. Our patterns include Dockerfile, *.dockerfile, Dockerfile.debug, Dockerfile.dev, Dockerfile.develop, Dockerfile.prod.

Our concern with Dockerfile.* is that developers might be using things like: Dockerfile.cs, Dockerfile.js, etc. A C# / JavaScript file isn't a Dockerfile (though, that's not a good name for it either).

You can locally override this behavior with a setting in either user or workspace settings.json:

"files.associations": {
    "Dockerfile.*": "dockerfile"
}

Using this option will allow for both syntax highlighting and the right-click -> Build Image (or, Build Image from command palette) commands.

[chrisdoherty4]

Understood, I totally see how that can be a problem.

Perhaps this ticket could be expanded to provide a feature that allows users to specify inclusions and exclusions (with a wildcard accepted) where exclusions take priority.

With such a feature you could define include: Dockerfile.* and exclude: Dockerfile.js, Dockerfile.cs etc.

I feel like it's quite common to use the Dockerfile.<descriptive word> approach for file names.

[bwateratmsft]

Exclusions would require a change from VSCode itself. However, I'm going to try to find out if Dockerfile.cs, etc. is actually a real-world problem. It may be better for those doing that to add a file association making Dockerfile.cs a csharp file.

[chrisdoherty4]

Understood. The .cs association sounds like a good idea! I wonder if file associations have some precedence ordering? I guess that'll be included in your query.

[bwateratmsft]

I tried it out.

1. I changed our file associations (in the extension) to Dockerfile.*
2. I created Dockerfile.cs
3. As expected, it was treated as a Dockerfile
4. I added the following file association:

{
    "files.associations": {
        "*.cs": "csharp"
    }
}

5. The Dockerfile.cs file was now treated as a C# file.

This behavior is good. I haven't researched yet how widespread this Dockerfile.cs antipattern is, but if it seems to be rare, then it's probably best to change the extension to use Dockerfile.*.

[bwateratmsft]

@BigMorty @chrisdoherty4 I looked at VSCode's telemetry some. It's not an exact science; Dockerfiles are detected based on MIME type and all we know is the file extension, not name.

Here's some data on the antipattern usage (last 30 days, limit 100K samples). I looked for any recognizable not-Dockerfile-extension (21 total):

File extension	Unique machine count
.yml	4
.dockerignore	3
.js	2
.json	2
.php	2
.yaml	2
.py	1
.js	1
.xml	1
.sh	1
.doc	1
.cs	1

(that .cs might have been us 😄)

In contrast here's the top 20. We cover the first six rows (64102 total), but miss everything else (132 total):

File extension	Unique machine count
	58904
.dockerfile	3915
.dev	943
.prod	256
.debug	43
.develop	41
.build	20
.base	17
.test	15
.docker	13
.local	10
.template	10
.amd64	9
.aarch64	6
.ci	6
.j2	6
.deploy	5
.df	5
.release	5
.txt	5

Given that users can override the default with a file association so that their not-Dockerfile is treated as a not-Dockerfile, it seems to me that we should change to Dockerfile.*. Beyond that top 20 there were at least 250 more smaller examples, it seems better to me to cater to a larger group (380+) who are using a correct pattern, rather than the smaller group (21) using the antipattern.

[bwateratmsft]

We discussed this in a meeting and decided to go ahead and make the change, given the data clearly supports it.

[chrisdoherty4]

Amazing! love that you brought data to the conversation.
What does your release cycle look like so I have an approximate time on when to expect 1.2.x to release?

[bwateratmsft]

@chrisdoherty4 Roughly monthly; 1.1.0 just released a few days ago...so about a month? (no promises!)

[bwateratmsft]

This change is now available in version 1.2.0 of the Docker extension.