✨ Add PR description generation

Add functionality to generate pull request descriptions.

- Add 'pr' subcommand to CLI for generating PR descriptions
- Implement logic to compare branches or analyze commit ranges
- Create service functions for generating PR descriptions from
  commits or branch differences.
- Implement MCP tool 'git_iris_pr' for generating PR descriptions.
- Update documentation and README files with usage instructions.

Author: hyperb1iss

README.md

@@ -353,6 +353,81 @@ The review includes:
   - Test Coverage - Analyzes test coverage gaps or brittle tests
   - Best Practices - Checks adherence to language-specific conventions and design guidelines
 
+### Generate Pull Request Descriptions
+
+Create comprehensive PR descriptions for changesets spanning multiple commits or single commits:
+
+```bash
+git-iris pr --from <from-ref> --to <to-ref>
+```
+
+Options:
+
+- `--from`: Starting Git reference (commit hash, tag, or branch name)
+- `--to`: Ending Git reference (defaults to HEAD if not specified)
+- `-i`, `--instructions`: Custom instructions for PR description generation
+- `--preset`: Select an instruction preset for PR description generation
+- `-p`, `--print`: Print the generated PR description to stdout and exit
+
+**Examples:**
+
+**Single commit analysis:**
+```bash
+# Analyze a single commit (compares against its parent)
+git-iris pr --from abc1234
+git-iris pr --to abc1234
+
+# Analyze a specific commitish (e.g., 2 commits ago)
+git-iris pr --to HEAD~2
+
+# Same commit for both from and to
+git-iris pr --from abc1234 --to abc1234
+```
+
+**Multiple commit analysis:**
+```bash
+# Review the last 3 commits together
+git-iris pr --from HEAD~3
+
+# Review commits from a specific point to now
+git-iris pr --from @~5
+```
+
+**Commit range analysis:**
+```bash
+git-iris pr --from v1.0.0 --to HEAD --preset detailed
+```
+
+**Branch comparison:**
+```bash
+git-iris pr --from main --to feature-auth --preset conventional
+```
+
+**Comparison to main:**
+```bash
+# Compare feature branch to main
+git-iris pr --to feature-branch
+```
+
+The PR description generator analyzes the entire changeset as an atomic unit rather than individual commits, providing:
+
+- A comprehensive title and summary
+- Detailed description of what was changed and why
+- List of commits included in the PR
+- Breaking changes identification
+- Testing notes and deployment considerations
+- Technical implementation details
+
+This is particularly useful for:
+- **Single commits**: Get detailed analysis of what changed in a specific commit or commitish (e.g., `HEAD~2`)
+- **Multiple commits**: Review a range of commits together (e.g., `--from HEAD~3` reviews the last 3 commits)
+- **Feature branches**: Get a complete overview of all changes in a feature
+- **Release preparations**: Understand what's included in a release candidate
+- **Code reviews**: Provide reviewers with comprehensive context
+- **Documentation**: Create detailed records of what changed between versions
+
+**Supported commitish syntax**: `HEAD~2`, `HEAD^`, `@~3`, `main~1`, `origin/main^`, and other Git commitish references.
+
 ### Generate Changelogs
 
 Create a detailed changelog between Git references:

docs/MCP.md

@@ -103,6 +103,75 @@ Example (remote URL):
 }
 ```
 
+### `git_iris_pr`
+
+Generate comprehensive pull request descriptions for changesets spanning multiple commits or single commits. Analyzes commits and changes as an atomic unit rather than individual commits. Supports Git commitish syntax like `HEAD~2`, `HEAD^`, `@~3`, etc.
+
+**Parameters:**
+
+- `from`: (string, required) Starting reference (commit hash, tag, branch name, or commitish)
+- `to`: (string) Ending reference (defaults to HEAD if not specified)
+- `preset`: (string) Preset instruction set to use for the PR description
+- `custom_instructions`: (string) Custom instructions for the AI
+- `repository`: (string, required) Repository path (local) or URL (remote). **Required.**
+
+Example (single commit analysis):
+
+```json
+{
+  "from": "abc1234",
+  "preset": "conventional",
+  "custom_instructions": "Focus on the specific changes made in this commit",
+  "repository": "/home/bliss/dev/myproject"
+}
+```
+
+Example (multiple commits using commitish):
+
+```json
+{
+  "from": "HEAD~3",
+  "preset": "conventional",
+  "custom_instructions": "Review the last 3 commits together as a cohesive change",
+  "repository": "/home/bliss/dev/myproject"
+}
+```
+
+Example (single commitish analysis):
+
+```json
+{
+  "to": "HEAD~2",
+  "preset": "detailed",
+  "custom_instructions": "Analyze what changed 2 commits ago",
+  "repository": "/home/bliss/dev/myproject"
+}
+```
+
+Example (branch comparison):
+
+```json
+{
+  "from": "main",
+  "to": "feature-auth",
+  "preset": "conventional",
+  "custom_instructions": "Highlight security implications and breaking changes",
+  "repository": "/home/bliss/dev/myproject"
+}
+```
+
+Example (commit range - remote URL):
+
+```json
+{
+  "from": "v1.0.0",
+  "to": "HEAD",
+  "preset": "detailed",
+  "custom_instructions": "Focus on user-facing changes",
+  "repository": "https://github.com/example/repo.git"
+}
+```
+
 ### `git_iris_changelog`
 
 Generate a detailed changelog between two Git references.

src/cli.rs

@@ -144,6 +144,38 @@ pub enum Commands {
         to: Option<String>,
     },
 
+    /// Generate a pull request description
+    #[command(
+        about = "Generate a pull request description using AI",
+        long_about = "Generate a comprehensive pull request description based on commit ranges, branch differences, or single commits. Analyzes the overall changeset as an atomic unit and creates professional PR descriptions with summaries, detailed explanations, and testing notes.\n\nUsage examples:\n• Single commit: --from abc1234 or --to abc1234\n• Single commitish: --from HEAD~1 or --to HEAD~2\n• Multiple commits: --from HEAD~3 (reviews last 3 commits)\n• Commit range: --from abc1234 --to def5678\n• Branch comparison: --from main --to feature-branch\n• From main to branch: --to feature-branch\n\nSupported commitish syntax: HEAD~2, HEAD^, @~3, main~1, origin/main^, etc."
+    )]
+    Pr {
+        #[command(flatten)]
+        common: CommonParams,
+
+        /// Print the generated PR description to stdout and exit
+        #[arg(
+            short,
+            long,
+            help = "Print the generated PR description to stdout and exit"
+        )]
+        print: bool,
+
+        /// Starting branch, commit, or commitish for comparison
+        #[arg(
+            long,
+            help = "Starting branch, commit, or commitish for comparison. For single commit analysis, specify just this parameter with a commit hash (e.g., --from abc1234). For reviewing multiple commits, use commitish syntax (e.g., --from HEAD~3 to review last 3 commits)"
+        )]
+        from: Option<String>,
+
+        /// Target branch, commit, or commitish for comparison
+        #[arg(
+            long,
+            help = "Target branch, commit, or commitish for comparison. For single commit analysis, specify just this parameter with a commit hash or commitish (e.g., --to HEAD~2)"
+        )]
+        to: Option<String>,
+    },
+
     /// Generate a changelog
     #[command(
         about = "Generate a changelog",
@@ -578,5 +610,31 @@ pub async fn handle_command(
             print,
         } => commands::handle_project_config_command(&common, model, token_limit, param, print),
         Commands::ListPresets => commands::handle_list_presets_command(),
+        Commands::Pr {
+            common,
+            print,
+            from,
+            to,
+        } => handle_pr(common, print, from, to, repository_url).await,
     }
 }
+
+/// Handle the `Pr` command
+async fn handle_pr(
+    common: CommonParams,
+    print: bool,
+    from: Option<String>,
+    to: Option<String>,
+    repository_url: Option<String>,
+) -> anyhow::Result<()> {
+    log_debug!(
+        "Handling 'pr' command with common: {:?}, print: {}, from: {:?}, to: {:?}",
+        common,
+        print,
+        from,
+        to
+    );
+    ui::print_version(crate_version!());
+    ui::print_newline();
+    commit::handle_pr_command(common, print, repository_url, from, to).await
+}