Add 'conda-remove-defaults' setting and support 'nodefaults' as a keyword channel

.github/workflows/example-14.yml

@@ -0,0 +1,54 @@
+name: "Example 14: Remove implicitly added channels"
+
+on:
+  pull_request:
+    branches:
+      - "*"
+  push:
+    branches:
+      - "develop"
+      - "main"
+      - "master"
+  schedule:
+    # Note that cronjobs run on master/main by default
+    - cron: "0 0 * * *"
+
+concurrency:
+  group:
+    ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true
+
+jobs:
+  example-14:
+    # prevent cronjobs from running on forks
+    if:
+      (github.event_name == 'schedule' && github.repository ==
+      'conda-incubator/setup-miniconda') || (github.event_name != 'schedule')
+    name: Ex14 (${{ matrix.os }}, ${{ matrix.no-implicit-channels }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["ubuntu-latest", "macos-latest", "windows-latest"]
+        no-implicit-channels: ["true", "false"]
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        id: setup-miniconda
+        continue-on-error: true
+        with:
+          channels: conda-forge
+          python-version: "3.12"
+          no-implicit-channels: ${{ matrix.no-implicit-channels }}
+      - shell: bash -el {0}
+        run: |
+          channels=$(conda config --show channels --json | jq -r '.channels | join(",")')
+          echo $channels
+          if [[ "${{ matrix.no-implicit-channels }}" == "true" ]]; then
+            if [[ "$channels" != "conda-forge" ]]; then
+              exit 1
+            fi
+          elif [[ "$channels" != "conda-forge,defaults" ]]; then
+              exit 1
+          fi

README.md

@@ -59,6 +59,7 @@ possibility of automatically activating the `test` environment on all shells.
 | [Caching packages](#caching-packages)                              | [![Caching Example Status][caching-badge]][caching]             |
 | [Caching environments](#caching-environments)                      | [![Caching Env Example Status][caching-env-badge]][caching-env] |
 | [Apple Silicon](#example-13-apple-silicon)                         | [![Apple Silicon][ex13-badge]][ex13]                            |
+| [No implicit channels](#example-14-no-implicit-channels)           | [![No implicit channels][ex14-badge]][ex14]                     |
 
 [ex1]:
   https://github.com/conda-incubator/setup-miniconda/actions/workflows/example-1.yml
@@ -112,6 +113,10 @@ possibility of automatically activating the `test` environment on all shells.
   https://github.com/conda-incubator/setup-miniconda/actions/workflows/example-13.yml
 [ex13-badge]:
   https://github.com/conda-incubator/setup-miniconda/actions/workflows/example-13.yml/badge.svg?branch=main
+[ex14]:
+  https://github.com/conda-incubator/setup-miniconda/actions/workflows/example-14.yml
+[ex14-badge]:
+  https://github.com/conda-incubator/setup-miniconda/actions/workflows/example-14.yml/badge.svg?branch=main
 
 ## Other Workflows
 
@@ -598,6 +603,35 @@ jobs:
           python -c "import platform; assert platform.machine() == 'arm64', platform.machine()"
 ```
 
+### Example 14: No implicit channels
+
+Workaround for this bug:
+[conda#12356](https://github.com/conda/conda/issues/12356).
+
+```yaml
+jobs:
+  example-13:
+    name: Ex14 (os=${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["ubuntu-latest"]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        id: setup-miniconda
+        continue-on-error: true
+        with:
+          miniforge-version: latest
+          channels: conda-forge
+          no-implicit-channels: "true"
+      - name: Check config
+        shell: bash -el {0}
+        run: |
+          conda config --show-sources
+```
+
 ## Caching
 
 ### Caching packages

action.yml

@@ -193,6 +193,12 @@ inputs:
       for more information."
     required: false
     default: ""
+  no-implicit-channels:
+    description:
+      "Postprocess channels list to remove channels that were not added
+      explicitly in the 'channels' setting. Will default to 'true' in 2025.03."
+    required: false
+    default: ""
   show-channel-urls:
     description:
       'Conda configuration. Show channel URLs when displaying what is going to

src/conda.ts

@@ -166,6 +166,20 @@ export async function applyCondaConfiguration(
     await condaCommand(["config", "--add", "channels", channel], options);
   }
 
+  if (inputs.noImplicitChannels === "true" && !channels.includes("defaults")) {
+    core.info("Removing implicitly added 'defaults' channel");
+    try {
+      await condaCommand(
+        ["config", "--remove", "channels", "defaults"],
+        options,
+      );
+    } catch (err) {
+      core.info(
+        "Removing defaults raised an error -- it was probably not present.",
+      );
+    }
+  }
+
   // All other options are just passed as their string representations
   for (const [key, value] of configEntries) {
     if (value.trim().length === 0 || key === "channels") {

src/input.ts

@@ -92,6 +92,7 @@ export async function parseInputs(): Promise<types.IActionInputs> {
     minicondaVersion: core.getInput("miniconda-version"),
     miniforgeVariant: core.getInput("miniforge-variant"),
     miniforgeVersion: core.getInput("miniforge-version"),
+    noImplicitChannels: core.getInput("no-implicit-channels"),
     pythonVersion: core.getInput("python-version"),
     removeProfiles: core.getInput("remove-profiles"),
     condaConfig: Object.freeze({

src/types.ts

@@ -84,6 +84,7 @@ export interface IActionInputs {
   readonly minicondaVersion: string;
   readonly miniforgeVariant: string;
   readonly miniforgeVersion: string;
+  readonly noImplicitChannels: string;
   readonly pythonVersion: string;
   readonly removeProfiles: string;
   readonly useMamba: string;