feat: create action

Hopefully it works?

README.md

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+# Nix Flake outputs size
+
+Use `nix path-info` to query the size of flake outputs and produce a markdown report.
+
+You can post this report as a comment to the PR associated with the current branch and/or export the report as a markdown artifact.
+
+Requires `nix`, `jq`, `curl`, `sed` and `coreutils` to be in path.
+
+## Usage
+
+```yaml
+- name: Generate size report
+  uses: https://git.salame.cl/jalil/nix-flake-outputs-size@main
+  with: # Default values
+    comment-on-pr: 'true'
+    generate-artifact: 'false'
+    artifact-name: 'size-report.md'
+```
+
+For more details see the [action.yaml](./action.yml) file.

action.yml

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+name: 'Nix Flake Outputs Size Report'
+author: Jalil David Salamé Messina
+description: |
+  Use `nix path-info` to query the size of flake outputs and produce a markdown
+  report.
+
+  You can post this report as a comment to the PR associated with the current
+  branch and/or export the report as a markdown artifact.
+
+  Requires `nix`, `jq`, `curl`, `sed` and `coreutils` to be in path.
+
+  Usage:
+
+  ```yaml
+  - name: Generate size report
+    uses: https://git.salame.cl/jalil/nix-flake-outputs-size@main
+    with: # Default values
+      comment-on-pr: 'true'
+      generate-artifact: 'false'
+      artifact-name: 'size-report.md'
+  ```
+inputs:
+  comment-on-pr:
+    description: Comment the report on the PR associated with the current branch.
+    default: 'true'
+  generate-artifact:
+    description: Export the generated markdown document as an artifact.
+    default: 'false'
+  artifact-name:
+    description: The name of the generated artifact.
+    default: 'size-report.md'
+outputs:
+runs:
+  using: 'composite'
+  steps:
+    - name: Create report
+      run: create-report.sh
+    - name: Upload Artifact
+      uses: https://code.forgejo.org/forgejo/upload-artifact@v4
+      if: input.generate-artifact
+      with:
+        path: size-report.md
+        name: input.artifact-name
+    - name: Upload Report
+      if: input.comment-on-pr
+      run: |
+        set -eu
+
+        # For push & tag events it'll bet GITHUB_REF_NAME, for pull_request events it'll be GITHUB_HEAD_REF
+        head_ref=${GITHUB_REF_NAME-$GITHUB_HEAD_REF}
+
+        pr_number=$(curl -X 'GET' \
+                "$GITHUB_API_URL/repos/$GITHUB_REPOSITORY/pulls?state=open&sort=recentupdate" \
+                -H 'accept: application/json' |
+                jq --arg head_ref "$head_ref" '.[] | select(.head.ref == $head_ref) | .number')
+
+        # Protect against running before a PR is made or if it is triggered on the main branch
+        if [ -z "$pr_number" ]; then
+                echo "No PR created for this commit"
+                exit 0
+        fi
+
+        echo "Retrieved index: $pr_number" >&2
+        echo "Expected PR URL: $GITHUB_SERVER_URL/$GITHUB_REPOSITORY/pulls/$pr_number" >&2
+
+        echo 'Generating comment body' >&2
+        comment=$(cat size-report.md)
+
+        echo 'Posting comment:' >&2
+        echo "$comment" >&2
+
+        echo 'Request data:' >&2
+        data=$(echo '{}' | jq --arg comment "$comment" '.body=$comment')
+        echo "$data" >&2
+        curl -o - -X 'POST' \
+                "$GITHUB_API_URL/repos/$GITHUB_REPOSITORY/issues/$pr_number/comments" \
+                -H 'accept: application/json' \
+                -H "Authorization: token $GITHUB_TOKEN" \
+                -H 'Content-Type: application/json' \
+                -d "$data"

create-report.sh

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+#!/bin/sh
+
+set -eu
+
+echo 'Retrieving Flake information' >&2
+flake_info=$(nix flake show --json 2>/dev/null)
+packages=$(
+	jq --raw-output '.packages."x86_64-linux" | keys[]' <<-EOF
+		$flake_info
+	EOF
+)
+echo "Packages:" >&2
+echo "$packages" >&2
+configurations=$(
+	jq --raw-output '.nixosConfigurations | keys[]' <<-EOF
+		$flake_info
+	EOF
+)
+echo "NixOS Configurations:" >&2
+echo "$configurations" >&2
+
+package_size_table() {
+	table='| Installable | NAR Size | Closure Size |
+|-------------|---------:|-------------:|
+'
+	for package in $packages; do
+		echo "Building $package" >&2
+		path=$(nix build --print-out-paths ".#$package" 2>/dev/null)
+		echo "Calculating size of $package" >&2
+		row=$(nix path-info --size --closure-size --human-readable "$path" 2>/dev/null |
+			sed "s/^\(\S\+\)\(\s\+\)\(\S\+\)\(\s\+\)\(\S\+\)$/| \`$package\` | \3 | \5 |/")
+		table="$table$row
+"
+	done
+
+	printf '%s' "$table"
+}
+
+configuration_size_table() {
+	table='| NixOS Configuration | NAR Size | Closure Size |
+|-------------|---------:|-------------:|
+'
+	for config in $configurations; do
+		echo "Building $config" >&2
+		path=$(nix build --print-out-paths ".#nixosConfigurations.$config.config.system.build.toplevel" 2>/dev/null)
+		echo "Calculating size of $config" >&2
+		row=$(nix path-info --size --closure-size --human-readable "$path" 2>/dev/null |
+			sed "s/^\(\S\+\)\(\s\+\)\(\S\+\)\(\s\+\)\(\S\+\)$/| \`$config\` | \3 | \5 |/")
+		table="$table$row
+"
+	done
+
+	printf '%s' "$table"
+}
+
+markdown() {
+	cat <<-EOF
+		## Outputs' size
+
+		### NixOS Configurations sizes
+
+		$(configuration_size_table)
+
+		### Package sizes
+
+		$(package_size_table)
+	EOF
+}
+
+markdown > size-report.md