Add read_to_string(path) function (#2507)

README.md

@@ -1842,6 +1842,8 @@ which will halt execution.
 - `path_exists(path)` - Returns `true` if the path points at an existing entity
   and `false` otherwise. Traverses symbolic links, and returns `false` if the
   path is inaccessible or points to a broken symlink.
+- `read_to_string(path)`<sup>master</sup> - Returns the content of file at
+  `path` as string.
 
 ##### Error Reporting
 

src/function.rs

@@ -87,6 +87,7 @@ pub(crate) fn get(name: &str) -> Option<Function> {
     "path_exists" => Unary(path_exists),
     "prepend" => Binary(prepend),
     "quote" => Unary(quote),
+    "read_to_string" => Unary(read_to_string),
     "replace" => Ternary(replace),
     "replace_regex" => Ternary(replace_regex),
     "semver_matches" => Binary(semver_matches),
@@ -528,6 +529,11 @@ fn quote(_context: Context, s: &str) -> FunctionResult {
   Ok(format!("'{}'", s.replace('\'', "'\\''")))
 }
 
+fn read_to_string(context: Context, filename: &str) -> FunctionResult {
+  fs::read_to_string(context.evaluator.context.working_directory().join(filename))
+    .map_err(|err| format!("I/O error reading `{filename}`: {err}"))
+}
+
 fn replace(_context: Context, s: &str, from: &str, to: &str) -> FunctionResult {
   Ok(s.replace(from, to))
 }

tests/functions.rs

@@ -1258,3 +1258,23 @@ fn style_unknown() {
     .status(EXIT_FAILURE)
     .run();
 }
+
+#[test]
+fn read_to_string() {
+  Test::new()
+    .justfile("foo := read_to_string('bar')")
+    .write("bar", "baz")
+    .args(["--evaluate", "foo"])
+    .stdout("baz")
+    .run();
+}
+
+#[test]
+fn read_to_string_not_found() {
+  Test::new()
+    .justfile("foo := read_to_string('bar')")
+    .args(["--evaluate", "foo"])
+    .stderr_regex(r"error: Call to function `read_to_string` failed: I/O error reading `bar`: .*")
+    .status(EXIT_FAILURE)
+    .run();
+}