feat: EvalState.realise_string

(cherry picked from commit f2b1142018fd64dd45ec97f1eccf0c48cc4a8c6d)

rust/nix-expr/src/eval_state.rs

@@ -3,6 +3,7 @@ use anyhow::Context as _;
 use anyhow::{bail, Result};
 use lazy_static::lazy_static;
 use nix_c_raw as raw;
+use nix_store::path::StorePath;
 use nix_store::store::Store;
 use nix_util::context::Context;
 use nix_util::string_return::callback_get_vec_u8;
@@ -34,6 +35,11 @@ pub fn init() -> Result<()> {
     }
 }
 
+pub struct RealisedString {
+    pub s: String,
+    pub paths: Vec<StorePath>,
+}
+
 pub struct EvalState {
     eval_state: NonNull<raw::EvalState>,
     store: Store,
@@ -131,6 +137,46 @@ impl EvalState {
         }
         self.get_string(value)
     }
+    pub fn realise_string(
+        &self,
+        value: &Value,
+        is_import_from_derivation: bool,
+    ) -> Result<RealisedString> {
+        let t = self.value_type(value)?;
+        if t != ValueType::String {
+            bail!("expected a string, but got a {:?}", t);
+        }
+
+        let rs = unsafe {
+            raw::string_realise(
+                self.context.ptr(),
+                self.raw_ptr(),
+                value.raw_ptr(),
+                is_import_from_derivation,
+            )
+        };
+        self.context.check_err()?;
+
+        let s = unsafe {
+            let start = raw::realised_string_get_buffer_start(rs) as *const u8;
+            let size = raw::realised_string_get_buffer_size(rs);
+            let slice = std::slice::from_raw_parts(start, size);
+            String::from_utf8(slice.to_vec())
+                .map_err(|e| anyhow::format_err!("Nix string is not valid UTF-8: {}", e))?
+        };
+
+        let paths = unsafe {
+            let n = raw::realised_string_get_store_path_count(rs);
+            let mut paths = Vec::with_capacity(n as usize);
+            for i in 0..n {
+                let path = raw::realised_string_get_store_path(rs, i);
+                paths.push(StorePath::new_raw_clone(path));
+            }
+            paths
+        };
+
+        Ok(RealisedString { s, paths })
+    }
 
     fn new_value_uninitialized(&self) -> Value {
         let value = unsafe { raw::alloc_value(self.context.ptr(), self.raw_ptr()) };
@@ -191,12 +237,24 @@ impl Drop for EvalState {
 #[cfg(test)]
 mod tests {
     use ctor::ctor;
+    use nix_util::settings;
 
     use super::*;
 
     #[ctor]
     fn setup() {
-        init().unwrap();
+        (|| -> Result<()> {
+            init()?;
+            // If it reinvokes the test suite,
+            // settings::set("build-hook", "")?;
+
+            // When testing in the sandbox, the default build dir would be a parent of the storeDir,
+            // which causes an error. So we set a custom build dir here.
+            settings::set("sandbox-build-dir", "/custom-build-dir-for-test")?;
+            Ok(())
+        })()
+        .unwrap();
+        std::env::set_var("_NIX_TEST_NO_SANDBOX", "1");
     }
 
     #[test]
@@ -356,4 +414,51 @@ mod tests {
         })
         .unwrap();
     }
+
+    #[test]
+    fn eval_state_realise_string() {
+        gc_registering_current_thread(|| {
+            let store = Store::open("auto").unwrap();
+            let es = EvalState::new(store).unwrap();
+            let expr = r#"
+                ''
+                    a derivation output: ${
+                        derivation { name = "letsbuild";
+                            system = builtins.currentSystem;
+                            builder = "/bin/sh";
+                            args = [ "-c" "echo foo > $out" ];
+                            }}
+                    a path: ${builtins.toFile "just-a-file" "ooh file good"}
+                    a derivation path by itself: ${
+                        builtins.unsafeDiscardOutputDependency 
+                            (derivation {
+                                name = "not-actually-built-yet";
+                                system = builtins.currentSystem;
+                                builder = "/bin/sh";
+                                args = [ "-c" "echo foo > $out" ];
+                            }).drvPath}
+                ''
+            "#;
+            let v = es.eval_from_string(expr, "<test>").unwrap();
+            es.force(&v).unwrap();
+            let rs = es.realise_string(&v, false).unwrap();
+
+            assert!(rs.s.starts_with("a derivation output:"));
+            assert!(rs.s.contains("-letsbuild\n"));
+            assert!(!rs.s.contains("-letsbuild.drv"));
+            assert!(rs.s.contains("a path:"));
+            assert!(rs.s.contains("-just-a-file"));
+            assert!(!rs.s.contains("-just-a-file.drv"));
+            assert!(!rs.s.contains("ooh file good"));
+            assert!(rs.s.ends_with("-not-actually-built-yet.drv\n"));
+
+            assert_eq!(rs.paths.len(), 3);
+            let mut names: Vec<String> = rs.paths.iter().map(|p| p.name().unwrap()).collect();
+            names.sort();
+            assert_eq!(names[0], "just-a-file");
+            assert_eq!(names[1], "letsbuild");
+            assert_eq!(names[2], "not-actually-built-yet.drv");
+        })
+        .unwrap();
+    }
 }