feat: PR description draft from config and forge templates

src/core/config.rs

@@ -28,6 +28,10 @@ pub struct ForgeConfig {
 pub struct RepoConfig {
     /// Base branch override (e.g. "origin/main"). Auto-detected if not set.
     pub base: Option<String>,
+    /// Path under the repo root to a markdown file seeding the PR/MR description editor.
+    /// `{{subject}}` is replaced with the commit title. If missing or empty, forge hints apply.
+    #[serde(default)]
+    pub pr_description_template: Option<String>,
 }
 
 impl Config {
@@ -38,6 +42,17 @@ impl Config {
         toml::from_str(&content).ok()
     }
 
+    /// Load config or defaults suitable for local-only flows (e.g. submit wizard).
+    pub fn load_or_default(repo_root: &Path) -> Self {
+        Self::load(repo_root).unwrap_or_else(|| Self {
+            forge: ForgeConfig {
+                forge_type: "github".to_string(),
+                submit_cmd: None,
+            },
+            repo: RepoConfig::default(),
+        })
+    }
+
     /// Save config to `.pilegit.toml`.
     pub fn save(&self, repo_root: &Path) -> Result<()> {
         let path = repo_root.join(CONFIG_FILE);
@@ -131,7 +146,10 @@ pub fn run_setup(repo_root: &Path) -> Result<Config> {
             forge_type,
             submit_cmd,
         },
-        repo: RepoConfig { base },
+        repo: RepoConfig {
+            base,
+            ..Default::default()
+        },
     };
 
     config.save(repo_root)?;
@@ -285,6 +303,7 @@ mod tests {
             },
             repo: RepoConfig {
                 base: Some("origin/develop".to_string()),
+                ..Default::default()
             },
         };
 
@@ -306,7 +325,10 @@ mod tests {
                 forge_type: "custom".to_string(),
                 submit_cmd: Some("arc diff HEAD^".to_string()),
             },
-            repo: RepoConfig { base: None },
+            repo: RepoConfig {
+                base: None,
+                ..Default::default()
+            },
         };
 
         config.save(&dir).unwrap();

src/forge/github.rs

@@ -216,6 +216,10 @@ impl Forge for GitHub {
 
         Ok(updates)
     }
+
+    fn pr_description_draft_hint(&self, repo: &Repo, _subject: &str) -> Option<String> {
+        crate::forge::pr_description::github_conventional_templates(repo)
+    }
 }
 
 impl GitHub {

src/forge/gitlab.rs

@@ -147,6 +147,10 @@ impl Forge for GitLab {
 
         Ok(updates)
     }
+
+    fn pr_description_draft_hint(&self, repo: &Repo, _subject: &str) -> Option<String> {
+        crate::forge::pr_description::gitlab_conventional_templates(repo)
+    }
 }
 
 impl GitLab {

src/forge/mod.rs

@@ -3,6 +3,7 @@ pub mod gitea;
 pub mod github;
 pub mod gitlab;
 pub mod phabricator;
+pub mod pr_description;
 pub mod stack_base_hint;
 
 use std::collections::HashMap;
@@ -76,6 +77,14 @@ pub trait Forge {
         true
     }
 
+    /// Optional seed for the PR/MR description editor (host template files, API, etc.).
+    /// Runs after `[repo].pr_description_template` if that file is missing or empty.
+    /// Use `None` to rely on config + built-in outline. Implement per forge in
+    /// [`crate::forge::pr_description`] helpers where conventions exist (GitHub, GitLab, …).
+    fn pr_description_draft_hint(&self, _repo: &Repo, _subject: &str) -> Option<String> {
+        None
+    }
+
     /// Extract trailers from a commit body that should be preserved during squash.
     /// Each forge knows its own trailer format (e.g. "Differential Revision:" for
     /// Phabricator, "Change-Id:" for Gerrit). Default: none.

src/forge/pr_description.rs

@@ -0,0 +1,154 @@
+//! Initial text for the PR/MR description editor: config path, forge-specific discovery, then builtin.
+
+use std::fs;
+use std::path::PathBuf;
+
+use crate::core::config::RepoConfig;
+use crate::git::ops::Repo;
+
+use super::Forge;
+
+/// Standard GitHub-style template locations (single-file; see GitHub docs for PR templates).
+const GITHUB_TEMPLATE_PATHS: &[&str] = &[
+    ".github/pull_request_template.md",
+    ".github/PULL_REQUEST_TEMPLATE.md",
+    "docs/pull_request_template.md",
+    "pull_request_template.md",
+];
+
+/// First existing non-empty file under `repo.workdir` from `relative_paths`, in order.
+pub(crate) fn read_first_repo_template(repo: &Repo, relative_paths: &[&str]) -> Option<String> {
+    for rel in relative_paths {
+        let path = repo.workdir.join(rel);
+        if let Ok(s) = fs::read_to_string(&path) {
+            if !s.trim().is_empty() {
+                return Some(s);
+            }
+        }
+    }
+    None
+}
+
+pub(crate) fn github_conventional_templates(repo: &Repo) -> Option<String> {
+    read_first_repo_template(repo, GITHUB_TEMPLATE_PATHS)
+}
+
+pub(crate) fn gitlab_conventional_templates(repo: &Repo) -> Option<String> {
+    let dir = repo.workdir.join(".gitlab/merge_request_templates");
+    let entries = fs::read_dir(&dir).ok()?;
+    let mut files: Vec<PathBuf> = entries
+        .filter_map(|e| e.ok())
+        .map(|e| e.path())
+        .filter(|p| p.extension().is_some_and(|ex| ex == "md"))
+        .collect();
+    if files.is_empty() {
+        return None;
+    }
+    files.sort();
+    let default_idx = files.iter().position(|p| {
+        p.file_name()
+            .and_then(|n| n.to_str())
+            .is_some_and(|n| n.eq_ignore_ascii_case("Default.md"))
+    });
+    let mut ordered = Vec::new();
+    if let Some(i) = default_idx {
+        ordered.push(files.remove(i));
+    }
+    ordered.extend(files);
+    for p in ordered {
+        if let Ok(s) = fs::read_to_string(&p) {
+            if !s.trim().is_empty() {
+                return Some(s);
+            }
+        }
+    }
+    None
+}
+
+fn substitute_subject(template: &str, subject: &str) -> String {
+    if template.contains("{{subject}}") {
+        template.replace("{{subject}}", subject)
+    } else {
+        template.to_string()
+    }
+}
+
+fn builtin_fallback(subject: &str) -> String {
+    format!("## Description\n\n{}\n\n## Test Plan\n\n\n", subject)
+}
+
+/// Editor seed for a new PR/MR: `[repo].pr_description_template` file, then
+/// [`Forge::pr_description_draft_hint`], then a small built-in outline.
+pub fn compose_initial_draft(
+    repo: &Repo,
+    forge: &dyn Forge,
+    repo_cfg: &RepoConfig,
+    subject: &str,
+) -> String {
+    if let Some(rel) = repo_cfg.pr_description_template.as_ref() {
+        let path = repo.workdir.join(rel);
+        if let Ok(s) = fs::read_to_string(&path) {
+            if !s.trim().is_empty() {
+                return substitute_subject(&s, subject);
+            }
+        }
+    }
+    if let Some(h) = forge.pr_description_draft_hint(repo, subject) {
+        return substitute_subject(&h, subject);
+    }
+    builtin_fallback(subject)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::forge::github::GitHub;
+
+    #[test]
+    fn github_reads_dot_github_lowercase() {
+        let dir =
+            std::env::temp_dir().join(format!("pgit-pr-template-test-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(dir.join(".github")).unwrap();
+        std::fs::write(
+            dir.join(".github/pull_request_template.md"),
+            "## Checklist\n\n- [ ] tests\n",
+        )
+        .unwrap();
+        let repo = Repo::at_dir(dir.clone());
+        let got = github_conventional_templates(&repo).unwrap();
+        assert!(got.contains("Checklist"));
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    #[test]
+    fn compose_prefers_config_path_over_forge() {
+        let dir = std::env::temp_dir().join(format!("pgit-pr-compose-test-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(dir.join(".github")).unwrap();
+        std::fs::write(dir.join(".github/pull_request_template.md"), "FORGE").unwrap();
+        std::fs::write(dir.join("custom.md"), "CONFIG {{subject}}").unwrap();
+        let repo = Repo::at_dir(dir.clone());
+        let cfg = RepoConfig {
+            base: None,
+            pr_description_template: Some("custom.md".to_string()),
+        };
+        let draft = compose_initial_draft(&repo, &GitHub, &cfg, "my feat");
+        assert_eq!(draft, "CONFIG my feat");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    #[test]
+    fn compose_falls_back_to_builtin() {
+        let dir =
+            std::env::temp_dir().join(format!("pgit-pr-fallback-test-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(&dir).unwrap();
+        let repo = Repo::at_dir(dir.clone());
+        let cfg = RepoConfig::default();
+        let draft = compose_initial_draft(&repo, &GitHub, &cfg, "only subject");
+        assert!(draft.contains("only subject"));
+        assert!(draft.contains("Test Plan"));
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+}

src/tui/mod.rs

@@ -47,13 +47,7 @@ pub fn run() -> Result<()> {
     let mut commits = repo.list_stack_commits()?;
 
     // Load config and create the forge integration
-    let config = Config::load(&repo.workdir).unwrap_or_else(|| Config {
-        forge: crate::core::config::ForgeConfig {
-            forge_type: "github".to_string(),
-            submit_cmd: None,
-        },
-        repo: crate::core::config::RepoConfig { base: None },
-    });
+    let config = Config::load_or_default(&repo.workdir);
     let f = forge::create_forge(&config);
 
     // Check that required CLI tools are installed
@@ -529,7 +523,13 @@ fn handle_submit_commit(
     }
 
     // Open pilegit's editor for PR description
-    let template = format!("## Description\n\n{}\n\n## Test Plan\n\n\n", subject);
+    let config = Config::load_or_default(&repo.workdir);
+    let template = forge::pr_description::compose_initial_draft(
+        &repo,
+        app.forge.as_ref(),
+        &config.repo,
+        subject,
+    );
 
     let tmp_path = std::env::temp_dir().join(format!("pgit-pr-msg-{}.txt", std::process::id()));
     std::fs::write(&tmp_path, &template)?;