Allow "choose from list" parameters in templates

crates/templates/src/constraints.rs

@@ -3,6 +3,7 @@ use regex::Regex;
 #[derive(Clone, Debug)]
 pub(crate) struct StringConstraints {
     pub regex: Option<Regex>,
+    pub allowed_values: Option<Vec<String>>,
 }
 
 impl StringConstraints {
@@ -12,6 +13,15 @@ impl StringConstraints {
                 anyhow::bail!("Input '{}' does not match pattern '{}'", text, regex);
             }
         }
+        if let Some(allowed_values) = self.allowed_values.as_ref() {
+            if !allowed_values.contains(&text) {
+                anyhow::bail!(
+                    "Input '{}' is not one of the allowed values ({})",
+                    text,
+                    allowed_values.join(", ")
+                );
+            }
+        }
         Ok(text)
     }
 }

crates/templates/src/interaction.rs

@@ -8,7 +8,7 @@ use crate::{
 
 use anyhow::anyhow;
 // use console::style;
-use dialoguer::{Confirm, Input};
+use dialoguer::{Confirm, Input, Select};
 
 pub(crate) trait InteractionStrategy {
     fn allow_generate_into(&self, target_dir: &Path) -> Cancellable<(), anyhow::Error>;
@@ -111,7 +111,10 @@ pub(crate) fn prompt_parameter(parameter: &TemplateParameter) -> Option<String>
 
     loop {
         let input = match parameter.data_type() {
-            TemplateParameterDataType::String(_) => ask_free_text(prompt, default_value),
+            TemplateParameterDataType::String(constraints) => match &constraints.allowed_values {
+                Some(allowed_values) => ask_choice(prompt, default_value, allowed_values),
+                None => ask_free_text(prompt, default_value),
+            },
         };
 
         match input {
@@ -138,6 +141,21 @@ fn ask_free_text(prompt: &str, default_value: &Option<String>) -> anyhow::Result
     Ok(result)
 }
 
+fn ask_choice(
+    prompt: &str,
+    default_value: &Option<String>,
+    allowed_values: &[String],
+) -> anyhow::Result<String> {
+    let mut select = Select::new().with_prompt(prompt).items(allowed_values);
+    if let Some(s) = default_value {
+        if let Some(default_index) = allowed_values.iter().position(|item| item == s) {
+            select = select.default(default_index);
+        }
+    }
+    let selected_index = select.interact()?;
+    Ok(allowed_values[selected_index].clone())
+}
+
 fn is_directory_empty(path: &Path) -> bool {
     if !path.exists() {
         return true;

crates/templates/src/reader.rs

@@ -86,6 +86,7 @@ pub(crate) struct RawParameter {
     #[serde(rename = "default")]
     pub default_value: Option<String>,
     pub pattern: Option<String>,
+    pub allowed_values: Option<Vec<String>>,
 }
 
 #[derive(Debug, Deserialize)]

crates/templates/src/template.rs

@@ -617,7 +617,10 @@ impl Condition {
 fn parse_string_constraints(raw: &RawParameter) -> anyhow::Result<StringConstraints> {
     let regex = raw.pattern.as_ref().map(|re| Regex::new(re)).transpose()?;
 
-    Ok(StringConstraints { regex })
+    Ok(StringConstraints {
+        regex,
+        allowed_values: raw.allowed_values.clone(),
+    })
 }
 
 fn read_install_record(layout: &TemplateLayout) -> InstalledFrom {