chore(third_party/crate2nix): run tests in /build/source r/7397

Cherry-pick of https://github.com/nix-community/crate2nix/pull/328. This
should fix rstest runs inside crate2nix-generated derivations.

Change-Id: I9d393768f7f764e33c5938bd8fa14bd1bb0b72e1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10650
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

2 files changed, 71 insertions, 0 deletions

diff --git a/third_party/overlays/patches/crate2nix-run-tests-in-build-source.patch b/third_party/overlays/patches/crate2nix-run-tests-in-build-source.patch
new file mode 100644
index 000000000000..52793270e6e8
--- /dev/null
+++ b/third_party/overlays/patches/crate2nix-run-tests-in-build-source.patch
@@ -0,0 +1,69 @@
+From 7cf084f73f7d15fe0538a625182fa7179c083b3d Mon Sep 17 00:00:00 2001
+From: Raito Bezarius <masterancpp@gmail.com>
+Date: Tue, 16 Jan 2024 02:10:48 +0100
+Subject: [PATCH] fix(template): run tests in `/build/source` instead `/build`
+
+Previously, the source tree was located inline in `/build` during tests, this was a mistake
+because the crates more than often are built in `/build/source` as per the `sourceRoot` system.
+
+This can cause issues with test binaries hardcoding `/build/source/...` as their choice for doing things,
+causing them to be confused in the test phase which is relocated without rewriting the paths inside test binaries.
+
+We fix that by relocating ourselves in the right hierarchy.
+
+This is a "simple" fix in the sense that more edge cases could exist but they are hard to reason about
+because they would be crates using custom `sourceRoot`, i.e. having `crate.sourceRoot` set and then it becomes
+a bit hard to reproduce the hierarchy, you need to analyze whether the path is absolute or relative,
+
+If it's relative, you can just reuse it and reproduce that specific hierarchy.
+If it's absolute, you need to cut the "absolute" meaningless part, e.g. `$NIX_BUILD_TOP/` and proceed like
+it's a relative path IMHO.
+---
+ crate2nix/Cargo.nix                                  | 10 ++++++++++
+ crate2nix/templates/nix/crate2nix/default.nix        | 10 ++++++++++
+
+diff --git a/Cargo.nix b/Cargo.nix
+index 6ef7a49..172ff34 100644
+--- a/Cargo.nix
++++ b/Cargo.nix
+@@ -2889,6 +2889,16 @@ rec {
+           # recreate a file hierarchy as when running tests with cargo
+ 
+           # the source for test data
++          # It's necessary to locate the source in $NIX_BUILD_TOP/source/
++          # instead of $NIX_BUILD_TOP/
++          # because we compiled those test binaries in the former and not the latter.
++          # So all paths will expect source tree to be there and not in the build top directly.
++          # For example: $NIX_BUILD_TOP := /build in general, if you ask yourself.
++          # TODO(raitobezarius): I believe there could be more edge cases if `crate.sourceRoot`
++          # do exist but it's very hard to reason about them, so let's wait until the first bug report.
++          mkdir -p source/
++          cd source/
++
+           ${pkgs.buildPackages.xorg.lndir}/bin/lndir ${crate.src}
+ 
+           # build outputs
+diff --git a/crate2nix/templates/nix/crate2nix/default.nix b/crate2nix/templates/nix/crate2nix/default.nix
+index e4fc2e9..dfb14c4 100644
+--- a/templates/nix/crate2nix/default.nix
++++ b/templates/nix/crate2nix/default.nix
+@@ -135,6 +135,16 @@ rec {
+           # recreate a file hierarchy as when running tests with cargo
+ 
+           # the source for test data
++          # It's necessary to locate the source in $NIX_BUILD_TOP/source/
++          # instead of $NIX_BUILD_TOP/
++          # because we compiled those test binaries in the former and not the latter.
++          # So all paths will expect source tree to be there and not in the build top directly.
++          # For example: $NIX_BUILD_TOP := /build in general, if you ask yourself.
++          # TODO(raitobezarius): I believe there could be more edge cases if `crate.sourceRoot`
++          # do exist but it's very hard to reason about them, so let's wait until the first bug report.
++          mkdir -p source/
++          cd source/
++
+           ${pkgs.buildPackages.xorg.lndir}/bin/lndir ${crate.src}
+ 
+           # build outputs
+-- 
+2.43.0
+
diff --git a/third_party/overlays/tvl.nix b/third_party/overlays/tvl.nix
index 0985bcb5a65c..9888fc449627 100644
--- a/third_party/overlays/tvl.nix
+++ b/third_party/overlays/tvl.nix
@@ -85,6 +85,8 @@ depot.nix.readTree.drvTargets {
       hash = "sha256-JTMe8GViCQt51WUiaaoIPmWtwEeeYrl6pBxo2DNuKig=";
     };
 
+    patches = [ ./patches/crate2nix-run-tests-in-build-source.patch ];
+
     sourceRoot = "${src.name}/crate2nix";
 
     cargoHash = "sha256-dhlSXY1CJE+JJt+6Y7W1MVMz36nwr6ny543py1TcjyY=";