From 53eb3225602f0f675e999968821b782caf36c7f8 Mon Sep 17 00:00:00 2001
From: Nicolas Mattia <nicolas@nmattia.com>
Date: Tue, 5 Nov 2024 10:05:57 +0100
Subject: [PATCH 1/5] Use relative directory for obj files hash

When producing `.o` files, the absolute path of each source file is
hashed and used as a prefix for the output object files. While this
avoids clashes between different source files with the same basenames,
this causes determinism issues in the build as the full system path
influences the build output.

This change strips the out_dir parent from the source file paths,
assuming that the source files are in the out_dir as well.
---
 src/command_helpers.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/command_helpers.rs b/src/command_helpers.rs
index 9f83e38c0..88776e685 100644
--- a/src/command_helpers.rs
+++ b/src/command_helpers.rs
@@ -311,6 +311,14 @@ pub(crate) fn objects_from_files(files: &[Arc<Path>], dst: &Path) -> Result<Vec<
         // Hash the dirname. This should prevent conflicts if we have multiple
         // object files with the same filename in different subfolders.
         let mut hasher = hash_map::DefaultHasher::new();
+
+        // Make the dirname relative to avoid full system paths influencing the sha and
+        // making the output system-dependent
+        let prefix = dst.parent().expect("Could not get parent of '{dst}'");
+        let prefix: &str = &prefix.to_string_lossy();
+        let err = format!("Could not strip prefix '{prefix}' from '{dirname}' to make '{dirname}' relative");
+        let dirname = dirname.strip_prefix(prefix).expect(&err);
+
         hasher.write(dirname.to_string().as_bytes());
         let obj = dst
             .join(format!("{:016x}-{}", hasher.finish(), basename))

From 9546e21ec43ba18ca5ad868a9f8d616955747fcc Mon Sep 17 00:00:00 2001
From: Nicolas Mattia <nicolas@nmattia.com>
Date: Thu, 7 Nov 2024 13:02:57 +0100
Subject: [PATCH 2/5] Strip CARGO_MANIFEST_DIR instead of parent

---
 src/command_helpers.rs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/command_helpers.rs b/src/command_helpers.rs
index 88776e685..0180613de 100644
--- a/src/command_helpers.rs
+++ b/src/command_helpers.rs
@@ -312,14 +312,14 @@ pub(crate) fn objects_from_files(files: &[Arc<Path>], dst: &Path) -> Result<Vec<
         // object files with the same filename in different subfolders.
         let mut hasher = hash_map::DefaultHasher::new();
 
-        // Make the dirname relative to avoid full system paths influencing the sha and
-        // making the output system-dependent
-        let prefix = dst.parent().expect("Could not get parent of '{dst}'");
-        let prefix: &str = &prefix.to_string_lossy();
-        let err = format!("Could not strip prefix '{prefix}' from '{dirname}' to make '{dirname}' relative");
-        let dirname = dirname.strip_prefix(prefix).expect(&err);
-
-        hasher.write(dirname.to_string().as_bytes());
+        // Make the dirname relative (if possible) to avoid full system paths influencing the sha
+        // and making the output system-dependent
+        let mut dirname = dirname.to_string();
+        if let Ok(root) = std::env::var("CARGO_MANIFEST_DIR") {
+            dirname = dirname.strip_prefix(&root).unwrap_or(&dirname).to_string();
+        }
+
+        hasher.write(dirname.as_bytes());
         let obj = dst
             .join(format!("{:016x}-{}", hasher.finish(), basename))
             .with_extension("o");

From dba1345fb3374c3488b505d7fe50ac8d95f2e060 Mon Sep 17 00:00:00 2001
From: Nicolas Mattia <nicolas@nmattia.com>
Date: Thu, 7 Nov 2024 14:33:34 +0100
Subject: [PATCH 3/5] Allow std::env::var

---
 src/command_helpers.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/command_helpers.rs b/src/command_helpers.rs
index 0180613de..b65c6376c 100644
--- a/src/command_helpers.rs
+++ b/src/command_helpers.rs
@@ -315,6 +315,10 @@ pub(crate) fn objects_from_files(files: &[Arc<Path>], dst: &Path) -> Result<Vec<
         // Make the dirname relative (if possible) to avoid full system paths influencing the sha
         // and making the output system-dependent
         let mut dirname = dirname.to_string();
+
+        // Here we allow using std::env::var (instead of Build::getenv) because
+        // CARGO_* variables always trigger a rebuild when changed
+        #[allow(clippy::disallowed_methods)]
         if let Ok(root) = std::env::var("CARGO_MANIFEST_DIR") {
             dirname = dirname.strip_prefix(&root).unwrap_or(&dirname).to_string();
         }

From e0f58fff79254a5f9befdc05b880e2249fd2f633 Mon Sep 17 00:00:00 2001
From: Nicolas Mattia <nicolas@nmattia.com>
Date: Thu, 7 Nov 2024 14:52:09 +0100
Subject: [PATCH 4/5] Implement review feedback

---
 src/command_helpers.rs | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/command_helpers.rs b/src/command_helpers.rs
index b65c6376c..5262e7405 100644
--- a/src/command_helpers.rs
+++ b/src/command_helpers.rs
@@ -314,14 +314,16 @@ pub(crate) fn objects_from_files(files: &[Arc<Path>], dst: &Path) -> Result<Vec<
 
         // Make the dirname relative (if possible) to avoid full system paths influencing the sha
         // and making the output system-dependent
-        let mut dirname = dirname.to_string();
-
-        // Here we allow using std::env::var (instead of Build::getenv) because
+        //
+        // NOTE: Here we allow using std::env::var (instead of Build::getenv) because
         // CARGO_* variables always trigger a rebuild when changed
         #[allow(clippy::disallowed_methods)]
-        if let Ok(root) = std::env::var("CARGO_MANIFEST_DIR") {
-            dirname = dirname.strip_prefix(&root).unwrap_or(&dirname).to_string();
-        }
+        let dirname = if let Some(root) = std::env::var_os("CARGO_MANIFEST_DIR") {
+            let root = root.to_string_lossy();
+            crate::Cow::Borrowed(dirname.strip_prefix(&*root).unwrap_or(&dirname))
+        } else {
+            dirname
+        };
 
         hasher.write(dirname.as_bytes());
         let obj = dst

From e05cedd73225c081c3ee383600bc6fa6a0fe14f7 Mon Sep 17 00:00:00 2001
From: Nicolas Mattia <nicolas@nmattia.com>
Date: Thu, 7 Nov 2024 16:15:51 +0100
Subject: [PATCH 5/5] Import std::borrow::Cow

---
 src/command_helpers.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/command_helpers.rs b/src/command_helpers.rs
index 5262e7405..adedab294 100644
--- a/src/command_helpers.rs
+++ b/src/command_helpers.rs
@@ -1,6 +1,7 @@
 //! Miscellaneous helpers for running commands
 
 use std::{
+    borrow::Cow,
     collections::hash_map,
     ffi::OsString,
     fmt::Display,
@@ -320,7 +321,7 @@ pub(crate) fn objects_from_files(files: &[Arc<Path>], dst: &Path) -> Result<Vec<
         #[allow(clippy::disallowed_methods)]
         let dirname = if let Some(root) = std::env::var_os("CARGO_MANIFEST_DIR") {
             let root = root.to_string_lossy();
-            crate::Cow::Borrowed(dirname.strip_prefix(&*root).unwrap_or(&dirname))
+            Cow::Borrowed(dirname.strip_prefix(&*root).unwrap_or(&dirname))
         } else {
             dirname
         };