Add choose function for generating random strings (#2049)

Cargo.toml

@@ -36,6 +36,7 @@ lexiclean = "0.0.1"
 libc = "0.2.0"
 log = "0.4.4"
 num_cpus = "1.15.0"
+rand = "0.8.5"
 regex = "1.10.4"
 semver = "1.0.20"
 serde = { version = "1.0.130", features = ["derive", "rc"] }

README.md

@@ -1517,6 +1517,13 @@ which will halt execution.
 
 [BLAKE3]: https://github.com/BLAKE3-team/BLAKE3/
 
+#### Random
+
+- `choose(n, alphabet)`<sup>master</sup> - Generate a string of `n` randomly
+  selected characters from `alphabet`, which may not contain repeated
+  characters. For example, `choose('64', HEX)` will generate a random
+  64-character lowercase hex string.
+
 #### Semantic Versions
 
 - `semver_matches(version, requirement)`<sup>1.16.0</sup> - Check whether a

src/function.rs

@@ -4,7 +4,9 @@ use {
     ToKebabCase, ToLowerCamelCase, ToShoutyKebabCase, ToShoutySnakeCase, ToSnakeCase, ToTitleCase,
     ToUpperCamelCase,
   },
+  rand::{seq::SliceRandom, thread_rng},
   semver::{Version, VersionReq},
+  std::collections::HashSet,
   Function::*,
 };
 
@@ -27,6 +29,7 @@ pub(crate) fn get(name: &str) -> Option<Function> {
     "cache_directory" => Nullary(|_| dir("cache", dirs::cache_dir)),
     "canonicalize" => Unary(canonicalize),
     "capitalize" => Unary(capitalize),
+    "choose" => Binary(choose),
     "clean" => Unary(clean),
     "config_directory" => Nullary(|_| dir("config", dirs::config_dir)),
     "config_local_directory" => Nullary(|_| dir("local config", dirs::config_local_dir)),
@@ -157,6 +160,30 @@ fn capitalize(_evaluator: &Evaluator, s: &str) -> Result<String, String> {
   Ok(capitalized)
 }
 
+fn choose(_evaluator: &Evaluator, n: &str, alphabet: &str) -> Result<String, String> {
+  if alphabet.is_empty() {
+    return Err("empty alphabet".into());
+  }
+
+  let mut chars = HashSet::<char>::with_capacity(alphabet.len());
+
+  for c in alphabet.chars() {
+    if !chars.insert(c) {
+      return Err(format!("alphabet contains repeated character `{c}`"));
+    }
+  }
+
+  let alphabet = alphabet.chars().collect::<Vec<char>>();
+
+  let n = n
+    .parse::<usize>()
+    .map_err(|err| format!("failed to parse `{n}` as positive integer: {err}"))?;
+
+  let mut rng = thread_rng();
+
+  Ok((0..n).map(|_| alphabet.choose(&mut rng).unwrap()).collect())
+}
+
 fn clean(_evaluator: &Evaluator, path: &str) -> Result<String, String> {
   Ok(Path::new(path).lexiclean().to_str().unwrap().to_owned())
 }

tests/functions.rs

@@ -661,6 +661,69 @@ fn uuid() {
     .run();
 }
 
+#[test]
+fn choose() {
+  Test::new()
+    .justfile(r#"x := choose('10', 'xXyYzZ')"#)
+    .args(["--evaluate", "x"])
+    .stdout_regex("^[X-Zx-z]{10}$")
+    .run();
+}
+
+#[test]
+fn choose_bad_alphabet_empty() {
+  Test::new()
+    .justfile("x := choose('10', '')")
+    .args(["--evaluate"])
+    .status(1)
+    .stderr(
+      "
+      error: Call to function `choose` failed: empty alphabet
+       ——▶ justfile:1:6
+        │
+      1 │ x := choose('10', '')
+        │      ^^^^^^
+    ",
+    )
+    .run();
+}
+
+#[test]
+fn choose_bad_alphabet_repeated() {
+  Test::new()
+    .justfile("x := choose('10', 'aa')")
+    .args(["--evaluate"])
+    .status(1)
+    .stderr(
+      "
+      error: Call to function `choose` failed: alphabet contains repeated character `a`
+       ——▶ justfile:1:6
+        │
+      1 │ x := choose('10', 'aa')
+        │      ^^^^^^
+    ",
+    )
+    .run();
+}
+
+#[test]
+fn choose_bad_length() {
+  Test::new()
+    .justfile("x := choose('foo', HEX)")
+    .args(["--evaluate"])
+    .status(1)
+    .stderr(
+      "
+      error: Call to function `choose` failed: failed to parse `foo` as positive integer: invalid digit found in string
+       ——▶ justfile:1:6
+        │
+      1 │ x := choose('foo', HEX)
+        │      ^^^^^^
+    ",
+    )
+    .run();
+}
+
 #[test]
 fn sha256() {
   Test::new()