fix: PathBuf -> AbsolutePathBuf in ConfigToml struct (#8205)

We should not have any `PathBuf` fields in `ConfigToml` or any of the
transitive structs we include, as we should use `AbsolutePathBuf`
instead so that we do not have to keep track of the file from which
`ConfigToml` was loaded such that we need it to resolve relative paths
later when the values of `ConfigToml` are used.

I only found two instances of this: `experimental_instructions_file` and
`experimental_compact_prompt_file`. Incidentally, when these were
specified as relative paths, they were resolved against `cwd` rather
than `config.toml`'s parent, which seems wrong to me. I changed the
behavior so they are resolved against the parent folder of the
`config.toml` being parsed, which we get "for free" due to the
introduction of `AbsolutePathBufGuard ` in
https://github.com/openai/codex/pull/7796.

While it is not great to change the behavior of a released feature,
these fields are prefixed with `experimental_`, which I interpret to
mean we have the liberty to change the contract.

For reference:

- `experimental_instructions_file` was introduced in
https://github.com/openai/codex/pull/1803
- `experimental_compact_prompt_file` was introduced in
https://github.com/openai/codex/pull/5959

codex-rs/core/src/config/mod.rs

@@ -26,7 +26,6 @@ use crate::project_doc::DEFAULT_PROJECT_DOC_FILENAME;
 use crate::project_doc::LOCAL_PROJECT_DOC_FILENAME;
 use crate::protocol::AskForApproval;
 use crate::protocol::SandboxPolicy;
-use crate::util::resolve_path;
 use codex_app_server_protocol::Tools;
 use codex_app_server_protocol::UserSavedConfig;
 use codex_protocol::config_types::ForcedLoginMethod;
@@ -692,8 +691,8 @@ pub struct ConfigToml {
     pub notice: Option<Notice>,
 
     /// Legacy, now use features
-    pub experimental_instructions_file: Option<PathBuf>,
+    pub experimental_instructions_file: Option<AbsolutePathBuf>,
-    pub experimental_compact_prompt_file: Option<PathBuf>,
+    pub experimental_compact_prompt_file: Option<AbsolutePathBuf>,
     pub experimental_use_unified_exec_tool: Option<bool>,
     pub experimental_use_rmcp_client: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
@@ -1132,9 +1131,8 @@ impl Config {
             .experimental_instructions_file
             .as_ref()
             .or(cfg.experimental_instructions_file.as_ref());
-        let file_base_instructions = Self::load_override_from_file(
+        let file_base_instructions = Self::try_read_non_empty_file(
             experimental_instructions_path,
-            &resolved_cwd,
             "experimental instructions file",
         )?;
         let base_instructions = base_instructions.or(file_base_instructions);
@@ -1144,9 +1142,8 @@ impl Config {
             .experimental_compact_prompt_file
             .as_ref()
             .or(cfg.experimental_compact_prompt_file.as_ref());
-        let file_compact_prompt = Self::load_override_from_file(
+        let file_compact_prompt = Self::try_read_non_empty_file(
             experimental_compact_prompt_path,
-            &resolved_cwd,
             "experimental compact prompt file",
         )?;
         let compact_prompt = compact_prompt.or(file_compact_prompt);
@@ -1278,21 +1275,21 @@ impl Config {
         None
     }
 
-    fn load_override_from_file(
+    /// If `path` is `Some`, attempts to read the file at the given path and
-        path: Option<&PathBuf>,
+    /// returns its contents as a trimmed `String`. If the file is empty, or
-        cwd: &Path,
+    /// is `Some` but cannot be read, returns an `Err`.
-        description: &str,
+    fn try_read_non_empty_file(
+        path: Option<&AbsolutePathBuf>,
+        context: &str,
     ) -> std::io::Result<Option<String>> {
-        let Some(p) = path else {
+        let Some(path) = path else {
             return Ok(None);
         };
 
-        let full_path = resolve_path(cwd, p);
+        let contents = std::fs::read_to_string(path).map_err(|e| {
-
-        let contents = std::fs::read_to_string(&full_path).map_err(|e| {
             std::io::Error::new(
                 e.kind(),
-                format!("failed to read {description} {}: {e}", full_path.display()),
+                format!("failed to read {context} {}: {e}", path.display()),
             )
         })?;
 
@@ -1300,7 +1297,7 @@ impl Config {
         if s.is_empty() {
             Err(std::io::Error::new(
                 std::io::ErrorKind::InvalidData,
-                format!("{description} is empty: {}", full_path.display()),
+                format!("{context} is empty: {}", path.display()),
             ))
         } else {
             Ok(Some(s))
@@ -2804,7 +2801,9 @@ model = "gpt-5.1-codex"
         std::fs::write(&prompt_path, "  summarize differently  ")?;
 
         let cfg = ConfigToml {
-            experimental_compact_prompt_file: Some(PathBuf::from("compact_prompt.txt")),
+            experimental_compact_prompt_file: Some(AbsolutePathBuf::from_absolute_path(
+                prompt_path,
+            )?),
             ..Default::default()
         };
 

codex-rs/core/src/config/profile.rs

@@ -1,5 +1,5 @@
+use codex_utils_absolute_path::AbsolutePathBuf;
 use serde::Deserialize;
-use std::path::PathBuf;
 
 use crate::protocol::AskForApproval;
 use codex_protocol::config_types::ReasoningSummary;
@@ -21,8 +21,8 @@ pub struct ConfigProfile {
     pub model_reasoning_summary: Option<ReasoningSummary>,
     pub model_verbosity: Option<Verbosity>,
     pub chatgpt_base_url: Option<String>,
-    pub experimental_instructions_file: Option<PathBuf>,
+    pub experimental_instructions_file: Option<AbsolutePathBuf>,
-    pub experimental_compact_prompt_file: Option<PathBuf>,
+    pub experimental_compact_prompt_file: Option<AbsolutePathBuf>,
     pub include_apply_patch_tool: Option<bool>,
     pub experimental_use_unified_exec_tool: Option<bool>,
     pub experimental_use_rmcp_client: Option<bool>,

docs/example-config.md

@@ -311,7 +311,7 @@ experimental_use_freeform_apply_patch = false
 # model_reasoning_summary = "auto"
 # model_verbosity = "medium"
 # chatgpt_base_url = "https://chatgpt.com/backend-api/"
-# experimental_compact_prompt_file = "compact_prompt.txt"
+# experimental_compact_prompt_file = "./compact_prompt.txt"
 # include_apply_patch_tool = false
 # experimental_use_freeform_apply_patch = false
 # tools_web_search = false