Support for experiment env vars (#1214)

* feat: experiments env var handling

* feat: read experiments from dotenv files

* docs: removed experimental cli flags

* feat: use vars instead of struct with reflection

docs/docs/experiments/experiments.md

@@ -21,13 +21,19 @@ are intended to replace.
 
 You can enable an experimental feature by:
 
-1. Using the `--x-{feature}` flag. This is intended for one-off invocations of
-   Task to test out experimental features. You can also disable a feature by
-   specifying a falsy value such as `--x-{feature}=false`.
-1. Using the `TASK_X_{FEATURE}=1` environment variable. This is intended for
-   permanently enabling experimental features in your environment.
+1. Using the relevant environment variable in front of a task command. For
+   example, `TASK_X_{FEATURE}=1 task {my-task}`. This is intended for one-off
+   invocations of Task to test out experimental features.
+1. Using the relevant environment variable in your "dotfiles" (e.g. `.bashrc`,
+   `.zshrc` etc.). This is intended for permanently enabling experimental
+   features in your environment.
+1. Creating a `.env` file in the same directory as your root Taskfile that
+   contains the relevant environment variables. e.g.
 
-Flags will always override environment variables.
+```shell
+# .env
+TASK_X_FEATURE=1
+```
 
 ## Current Experimental Features and Deprecations
 
@@ -38,11 +44,11 @@ existing Taskfiles to the new behavior.
 
 <!-- EXPERIMENT TEMPLATE - Include sections as necessary...
 
-### ![experiment] <Feature> ([#{issue}](https://github.com/go-task/task/issues/{issue})), ...)
+### ![experiment] {Feature} ([#{issue}](https://github.com/go-task/task/issues/{issue})), ...)
 
-- Flag to enable: `--x-{feature}`
-- Env to enable: `TASK_X_{feature}`
+- Environment variable: `TASK_X_{feature}`
 - Deprecates: {list any existing functionality that will be deprecated by this experiment}
+- Breaks: {list any existing functionality that will be broken by this experiment}
 
 {Short description of the feature}
 

internal/experiments/experiments.go

@@ -0,0 +1,43 @@
+package experiments
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/joho/godotenv"
+)
+
+const envPrefix = "TASK_X_"
+
+var TestExperiment bool
+
+func init() {
+	if err := readDotEnv(); err != nil {
+		panic(err)
+	}
+	TestExperiment = parseEnv("TestExperiment")
+}
+
+func parseEnv(xName string) bool {
+	envName := fmt.Sprintf("%s%s", envPrefix, xName)
+	return os.Getenv(envName) == "1"
+}
+
+func readDotEnv() error {
+	env, err := godotenv.Read()
+	if errors.Is(err, os.ErrNotExist) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	// If the env var is an experiment, set it.
+	for key, value := range env {
+		if strings.HasPrefix(key, envPrefix) {
+			os.Setenv(key, value)
+		}
+	}
+	return nil
+}