From 82e708c19230f77fbb5ea01157fc1226e72119de Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <silvan.mosberger@tweag.io>
Date: Tue, 24 Oct 2023 19:27:48 +0200
Subject: tests.nixpkgs-check-by-name: Custom Validation type and improvements

Co-authored-by: Wanja Hentze
---
 pkgs/test/nixpkgs-check-by-name/src/validation.rs | 102 ++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 pkgs/test/nixpkgs-check-by-name/src/validation.rs

(limited to 'pkgs/test/nixpkgs-check-by-name/src/validation.rs')

diff --git a/pkgs/test/nixpkgs-check-by-name/src/validation.rs b/pkgs/test/nixpkgs-check-by-name/src/validation.rs
new file mode 100644
index 00000000000..e7279385152
--- /dev/null
+++ b/pkgs/test/nixpkgs-check-by-name/src/validation.rs
@@ -0,0 +1,102 @@
+use crate::nixpkgs_problem::NixpkgsProblem;
+use itertools::concat;
+use itertools::{
+    Either::{Left, Right},
+    Itertools,
+};
+use Validation::*;
+
+/// The validation result of a check.
+/// Instead of exiting at the first failure,
+/// this type can accumulate multiple failures.
+/// This can be achieved using the functions `and`, `sequence` and `sequence_`
+///
+/// This leans on https://hackage.haskell.org/package/validation
+pub enum Validation<A> {
+    Failure(Vec<NixpkgsProblem>),
+    Success(A),
+}
+
+impl<A> From<NixpkgsProblem> for Validation<A> {
+    /// Create a `Validation<A>` from a single check problem
+    fn from(value: NixpkgsProblem) -> Self {
+        Failure(vec![value])
+    }
+}
+
+/// A type alias representing the result of a check, either:
+/// - Err(anyhow::Error): A fatal failure, typically I/O errors.
+///   Such failures are not caused by the files in Nixpkgs.
+///   This hints at a bug in the code or a problem with the deployment.
+/// - Ok(Failure(Vec<NixpkgsProblem>)): A non-fatal validation problem with the Nixpkgs files.
+///   Further checks can be run even with this result type.
+///   Such problems can be fixed by changing the Nixpkgs files.
+/// - Ok(Success(A)): A successful (potentially intermediate) result with an arbitrary value.
+///   No fatal errors have occurred and no validation problems have been found with Nixpkgs.
+pub type Result<A> = anyhow::Result<Validation<A>>;
+
+pub trait ResultIteratorExt<A, E>: Sized + Iterator<Item = std::result::Result<A, E>> {
+    fn collect_vec(self) -> std::result::Result<Vec<A>, E>;
+}
+
+impl<I, A, E> ResultIteratorExt<A, E> for I
+where
+    I: Sized + Iterator<Item = std::result::Result<A, E>>,
+{
+    /// A convenience version of `collect` specialised to a vector
+    fn collect_vec(self) -> std::result::Result<Vec<A>, E> {
+        self.collect()
+    }
+}
+
+impl<A> Validation<A> {
+    /// Map a `Validation<A>` to a `Validation<B>` by applying a function to the
+    /// potentially contained value in case of success.
+    pub fn map<B>(self, f: impl FnOnce(A) -> B) -> Validation<B> {
+        match self {
+            Failure(err) => Failure(err),
+            Success(value) => Success(f(value)),
+        }
+    }
+}
+
+impl Validation<()> {
+    /// Combine two validations, both of which need to be successful for the return value to be successful.
+    /// The `NixpkgsProblem`s of both sides are returned concatenated.
+    pub fn and<A>(self, other: Validation<A>) -> Validation<A> {
+        match (self, other) {
+            (Success(_), Success(right_value)) => Success(right_value),
+            (Failure(errors), Success(_)) => Failure(errors),
+            (Success(_), Failure(errors)) => Failure(errors),
+            (Failure(errors_l), Failure(errors_r)) => Failure(concat([errors_l, errors_r])),
+        }
+    }
+}
+
+/// Combine many validations into a single one.
+/// All given validations need to be successful in order for the returned validation to be successful,
+/// in which case the returned validation value contains a `Vec` of each individual value.
+/// Otherwise the `NixpkgsProblem`s of all validations are returned concatenated.
+pub fn sequence<A>(check_results: impl IntoIterator<Item = Validation<A>>) -> Validation<Vec<A>> {
+    let (errors, values): (Vec<Vec<NixpkgsProblem>>, Vec<A>) = check_results
+        .into_iter()
+        .partition_map(|validation| match validation {
+            Failure(err) => Left(err),
+            Success(value) => Right(value),
+        });
+
+    // To combine the errors from the results we flatten all the error Vec's into a new Vec
+    // This is not very efficient, but doesn't matter because generally we should have no errors
+    let flattened_errors = errors.into_iter().concat();
+
+    if flattened_errors.is_empty() {
+        Success(values)
+    } else {
+        Failure(flattened_errors)
+    }
+}
+
+/// Like `sequence`, but without any containing value, for convenience
+pub fn sequence_(validations: impl IntoIterator<Item = Validation<()>>) -> Validation<()> {
+    sequence(validations).map(|_| ())
+}
-- 
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