chore(task): expand on concepts and usage

knowledge base/task.md

@@ -3,6 +3,12 @@
 Task runner aiming to be simpler and easier to use than [GNU Make].
 
 1. [TL;DR](#tldr)
+1. [Usage](#usage)
+1. [Variables](#variables)
+1. [Call other tasks](#call-other-tasks)
+   1. [Call root tasks from non-flattened included files](#call-root-tasks-from-non-flattened-included-files)
+1. [Troubleshooting](#troubleshooting)
+   1. [Dry run does not print the commands that would be executed](#dry-run-does-not-print-the-commands-that-would-be-executed)
 1. [Further readings](#further-readings)
    1. [Sources](#sources)
 
@@ -12,7 +18,7 @@ Taskfiles are Task's Makefile counterpart.<br/>
 Taskfiles are written in YAML.
 
 Task leverages `mvdan.cc/sh` to run commands, which is a native Go shell interpreter.<br/>
-This allows to write `sh`/`bash` commands and have them work even where `sh` or `bash` are usually not available (e.g.:
+It allows to write `sh`/`bash` commands and have them work even where `sh` or `bash` are usually not available (e.g.:
 Windows) as long as any called executable is available in `PATH`.
 
 Pros:
@@ -30,6 +36,12 @@ Cons:
   That makes them very much similar to \[[Gitlab] / [Azure Devops]]'s pipelines, and if one has any experience with them
   one knows what a pain that can be.
 
+Uses Go's [text/template] package to interpolate values.
+
+Environment variables (`env: {}, dotenv: []`) are available in the shell used by commands.<br/>
+Variables (`vars: {}`) are **only** available to Task while executing templates, but **will default to environment
+variables** with the same name.
+
 <details>
   <summary>Setup</summary>
 
@@ -46,39 +58,200 @@ zypper install 'https://github.com/go-task/task/releases/download/v3.39.2/task_l
 task --completion 'fish' > ~/'.config/fish/completions/task.fish'
 task --completion 'zsh'  > '/usr/local/share/zsh/site-functions/_task'
 task --completion 'bash' > '/etc/bash_completion.d/task'
+
+# Create a new 'Taskfile.yml' file in the current folder.
+task --init
 ```
 
 </details>
 <details>
   <summary>Usage</summary>
 
+```sh
+# Run tasks.
+# No tasks given --> assumed one named 'default'
+task
+task 'assets'
+task -v 'build:python' 'deploy:app'
+
+# Simulate running tasks.
+task -n 'bootstrap'
+task --dry --verbose 'lint' 'validate:ansible'
+```
+
+</details>
+
+## Usage
+
 1. Create a file called `Taskfile.yml`, `taskfile.yml`, `Taskfile.yaml`, `taskfile.yaml`, `Taskfile.dist.yml`,
    `taskfile.dist.yml`, `Taskfile.dist.yaml`, or `taskfile.dist.yaml` (ordered by priority) in the root of one's
-   project.<br/>
-   The `cmds` keys shall contain the commands for their own tasks:
-
-   ```yaml
-   version: '3'
-
-   tasks:
-     build:
-       cmds:
-         - go build -v -i main.go
-
-     assets:
-       cmds:
-         - esbuild --bundle --minify css/index.css > public/bundle.css
-   ```
+   project.
 
 1. Run tasks by their name:
 
    ```sh
-   task 'assets' 'build'
+   task 'assets' 'build:python'
    task --dry 'bootstrap'
    ```
 
    If task names are omitted, a task named `default` will be assumed.
 
+## Variables
+
+Set **environment** variables at global or task level with `env: {}`.<br/>
+They are made available in the shell used by commands.
+
+<details style="padding: 0 0 1em 1em;">
+
+```yml
+env:
+  SOME_VAR: some DEFAULT value
+tasks:
+  env_vars:test:
+    env:
+      SOME_VAR: some value
+    cmds:
+      - echo $SOME_VAR
+```
+
+</details>
+
+**Exported** and **command-specific** shell variables **take precedence** over the ones defined in the Taskfile.
+
+<details style="padding: 0 0 1em 1em;">
+
+```sh
+$ task env_vars:test
+some value
+
+$ set SOME_VAR 'some OTHER value'
+$ task env_vars:test
+some value
+
+$ set -x SOME_VAR 'some OTHER value'
+$ task env_vars:test
+some OTHER value
+
+$ SOME_VAR='some EPHEMERAL value' task env_vars:test
+some EPHEMERAL value
+```
+
+</details>
+
+Task accepts setting environment variables **inside** the command itself like `make` due to some shells not supporting
+the usual syntax.
+
+<details style="padding: 0 0 1em 1em;">
+
+```sh
+# These are equivalent
+CONTENT='Hello, World!' FILE=file.txt MESSAGE="All done!" task write-file print
+task write-file FILE=file.txt "CONTENT=Hello, World!" print "MESSAGE=All done!"
+```
+
+</details>
+
+Include **environment** variables from `.env`-like files at global or task level with `dotenv: []`.<br/>
+Non-existing files are **ignored** in a similar manner to `make`'s `-include` directive (with the prefixed dash).
+
+<details style="padding: 0 0 1em 1em;">
+
+```yml
+dotenv:
+  - .env
+  - .env.local
+tasks:
+  env_vars:test:
+    dotenv:
+      - .env.task
+      - .env.task.local
+```
+
+</details>
+
+Environment variables set in `env: {}` **take precedence** over the ones loaded from `dotenv` **at the same level**.
+
+```mermaid
+graph LR
+  gd["`dotenv: []`"] --- ge["`env: {}`"]
+  ge["`env: {}`"] --- td["`task.dotenv: []`"]
+  td["`task.dotenv: []`"] --- te["`task.env: {}`"]
+  te["`task.env: {}`"] --- se["`shell.export`"]
+  se["`shell.export`"] --- ce["`command.env`"]
+```
+
+<br/>
+
+Variables (`vars: {}`) are **only** available to Task while executing templates, but **will default to environment
+variables** with the same name.
+
+Task execution looks for variables in the following order (first-come-first-served):
+
+- Variables declared in the task's definition.
+- Variables provided when calling a task from another.
+- Variables defined in included Taskfiles.
+- Variables provided when including Taskfiles.
+- Global variables.
+- Environment variables.
+
+```mermaid
+graph LR
+  ev["`environment variables`"] --- gv["`vars: {}`"]
+  gv["`vars: {}`"] --- iv["`includes[].vars: {}`"]
+  iv["`includes[].vars: {}`"] --- it["`includes[]`"]
+  it["`includes[]`"] --- tc["`task.cmd.'task'`"]
+  tc["`task.cmd.'task'`"] --- te["`task.env`"]
+```
+
+## Call other tasks
+
+Use `task:` followed by the call**ed** task name as the command in the call**ing** task.
+
+```yml
+tasks:
+  task:being:called: { … }
+  task:calling:
+    cmd: task: task:being:called
+```
+
+### Call root tasks from non-flattened included files
+
+Refer an empty namespace by prepending the name of the task with `:`.
+
+```yml
+# $ROOT/Taskfile.yml
+includes:
+  subproject:
+    taskfile: subproject
+    dir: subproject
+tasks:
+  task:of:interest: { … }
+```
+
+```yml
+# $ROOT/subproject/Taskfile.yml
+tasks:
+  some:task:
+    cmd:
+      task: :task:of:interest
+```
+
+## Troubleshooting
+
+### Dry run does not print the commands that would be executed
+
+<details>
+  <summary>Root cause</summary>
+
+Command simulations do **not** print commands to output when setting `silent: true` at any level.
+
+</details>
+
+<details>
+  <summary>Solution</summary>
+
+Force the print using `-v, --verbose` when `silent` is set to `true`, or set it to `false` at task level.
+
 </details>
 
 ## Further readings
@@ -112,3 +285,4 @@ task --completion 'bash' > '/etc/bash_completion.d/task'
 <!-- Others -->
 [demystification of taskfile variables]: https://medium.com/@TianchenW/demystification-of-taskfile-variables-29b751950393
 [stop using makefile (use taskfile instead)]: https://dev.to/calvinmclean/stop-using-makefile-use-taskfile-instead-4hm9
+[text/template]: https://pkg.go.dev/text/template

templates/Taskfile.yml

@@ -26,6 +26,13 @@ tasks:
       - task: python:update-venv
       - npm update --save
 
+  env:debug:
+    desc: print the current shell environment
+    summary: Print the current shell environment
+    cmds:
+      - printenv | sort
+      - set | sort
+
   python:venv:create:
     vars:
       PYTHON_VERSION: '{{ .PYTHON_VERSION | default 3.12}}'