Update diff example to allow basic diffing of blobs.

This could be improved by adding color support, etc.

Author: staktrace

examples/diff.rs

@@ -14,8 +14,8 @@
 
 #![deny(warnings)]
 
-use git2::{Diff, DiffOptions, Error, Object, ObjectType, Repository};
-use git2::{DiffFindOptions, DiffFormat};
+use git2::{Blob, Diff, DiffOptions, Error, Object, ObjectType, Oid, Repository};
+use git2::{DiffDelta, DiffFindOptions, DiffFormat, DiffHunk, DiffLine};
 use std::str;
 use structopt::StructOpt;
 
@@ -26,6 +26,9 @@ struct Args {
     arg_from_oid: Option<String>,
     #[structopt(name = "to_oid")]
     arg_to_oid: Option<String>,
+    #[structopt(name = "blobs", long)]
+    /// treat from_oid and to_oid as blob ids
+    flag_blobs: bool,
     #[structopt(name = "patch", short, long)]
     /// show output in patch format
     flag_patch: bool,
@@ -137,6 +140,11 @@ enum Cache {
     None,
 }
 
+fn print_diff(_delta: DiffDelta, _hunk: Option<DiffHunk>, line: DiffLine) -> bool {
+    print!("{}{}", line.origin(), str::from_utf8(line.content()).unwrap());
+    true
+}
+
 fn run(args: &Args) -> Result<(), Error> {
     let path = args.flag_git_dir.as_ref().map(|s| &s[..]).unwrap_or(".");
     let repo = Repository::open(path)?;
@@ -171,6 +179,23 @@ fn run(args: &Args) -> Result<(), Error> {
         opts.id_abbrev(40);
     }
 
+    if args.flag_blobs {
+        let b1 = resolve_blob(&repo, args.arg_from_oid.as_ref())?;
+        let b2 = resolve_blob(&repo, args.arg_to_oid.as_ref())?;
+        repo.diff_blobs(
+            b1.as_ref(),
+            None,
+            b2.as_ref(),
+            None,
+            Some(&mut opts),
+            None,
+            None,
+            None,
+            Some(&mut print_diff),
+        )?;
+        return Ok(());
+    }
+
     // Prepare the diff to inspect
     let t1 = tree_to_treeish(&repo, args.arg_from_oid.as_ref())?;
     let t2 = tree_to_treeish(&repo, args.arg_to_oid.as_ref())?;
@@ -292,6 +317,17 @@ fn tree_to_treeish<'a>(
     Ok(Some(tree))
 }
 
+fn resolve_blob<'a>(
+    repo: &'a Repository,
+    arg: Option<&String>,
+) -> Result<Option<Blob<'a>>, Error> {
+    let arg = match arg {
+        Some(s) => Oid::from_str(s)?,
+        None => return Ok(None),
+    };
+    repo.find_blob(arg).map(|b| Some(b))
+}
+
 impl Args {
     fn cache(&self) -> Cache {
         if self.flag_cached {