patch_sync: Add patch_parsing module

At present, the patch_sync code does nothing as the base version
only sets up the code for future reviews.

This adds in the ability to parse the PATCHES.json files, check
the differences across past versions, and transpose those patches
to another repo.

This parsing assumes the PATCHES.json now use the uniform schema,
which the AOSP currently does, but CrOS may not by the time this
commit lands.

BUG=b:209493133
TEST=cargo build
TEST=cargo test

Change-Id: I8de01eae3d9555dbb000378516a5bf38e29fea8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/3339405
Reviewed-by: George Burgess <gbiv@chromium.org>
Tested-by: Jordan Abrahams <ajordanr@google.com>
Commit-Queue: Jordan Abrahams <ajordanr@google.com>

2 files changed, 240 insertions, 10 deletions

diff --git a/llvm_tools/patch_sync/src/main.rs b/llvm_tools/patch_sync/src/main.rs
index 8eedaaa8..514f054f 100644
--- a/llvm_tools/patch_sync/src/main.rs
+++ b/llvm_tools/patch_sync/src/main.rs
@@ -1,3 +1,4 @@
+mod patch_parsing;
 mod version_control;
 
 use anyhow::{Context, Result};
@@ -45,13 +46,43 @@ fn transpose_subcmd(args: TransposeOpt) -> Result<()> {
         sync_before: false,
     };
     ctx.setup()?;
-    let _cros_patches_path = ctx.cros_patches_path();
-    let _android_patches_path = ctx.android_patches_path();
+    let cros_patches_path = ctx.cros_patches_path();
+    let android_patches_path = ctx.android_patches_path();
+
+    // Chromium OS Patches ----------------------------------------------------
+    let mut cur_cros_collection =
+        patch_parsing::PatchCollection::parse_from_file(&cros_patches_path)
+            .context("parsing cros PATCHES.json")?;
+    let new_cros_patches: patch_parsing::PatchCollection = {
+        let cros_old_patches_json = ctx.old_cros_patch_contents(&args.old_cros_ref)?;
+        let old_cros_collection = patch_parsing::PatchCollection::parse_from_str(
+            cros_patches_path.parent().unwrap().to_path_buf(),
+            &cros_old_patches_json,
+        )?;
+        cur_cros_collection.subtract(&old_cros_collection)?
+    };
+
+    // Android Patches -------------------------------------------------------
+    let mut cur_android_collection =
+        patch_parsing::PatchCollection::parse_from_file(&android_patches_path)
+            .context("parsing android PATCHES.json")?;
+    let new_android_patches: patch_parsing::PatchCollection = {
+        let android_old_patches_json = ctx.old_android_patch_contents(&args.old_android_ref)?;
+        let old_android_collection = patch_parsing::PatchCollection::parse_from_str(
+            android_patches_path.parent().unwrap().to_path_buf(),
+            &android_old_patches_json,
+        )?;
+        cur_android_collection.subtract(&old_android_collection)?
+    };
+
+    // Transpose Patches -----------------------------------------------------
+    new_cros_patches.transpose_write(&mut cur_cros_collection)?;
+    new_android_patches.transpose_write(&mut cur_android_collection)?;
 
     if !args.no_commit {
         return Ok(());
     }
-    // Commit and upload for review.
+    // Commit and upload for review ------------------------------------------
     ctx.cros_repo_upload()
         .context("uploading chromiumos changes")?;
     ctx.android_repo_upload()
@@ -73,34 +104,34 @@ enum Opt {
     /// Transpose patches from two PATCHES.json files
     /// to each other.
     Transpose {
-        #[structopt(long = "cros-checkout", parse(from_os_str))]
         /// Path to the ChromiumOS source repo checkout.
+        #[structopt(long = "cros-checkout", parse(from_os_str))]
         cros_checkout_path: PathBuf,
 
-        #[structopt(long = "overlay-base-ref")]
         /// Git ref (e.g. hash) for the ChromiumOS overlay to use as the base.
+        #[structopt(long = "overlay-base-ref")]
         old_cros_ref: String,
 
-        #[structopt(long = "aosp-checkout", parse(from_os_str))]
         /// Path to the Android Open Source Project source repo checkout.
+        #[structopt(long = "aosp-checkout", parse(from_os_str))]
         android_checkout_path: PathBuf,
 
-        #[structopt(long = "aosp-base-ref")]
         /// Git ref (e.g. hash) for the llvm_android repo to use as the base.
+        #[structopt(long = "aosp-base-ref")]
         old_android_ref: String,
 
-        #[structopt(short, long)]
         /// Print information to stdout
+        #[structopt(short, long)]
         verbose: bool,
 
-        #[structopt(long)]
         /// Do not change any files. Useful in combination with `--verbose`
         /// Implies `--no-commit` and `--no-upload`.
+        #[structopt(long)]
         dry_run: bool,
 
-        #[structopt(long)]
         /// Do not commit any changes made.
         /// Implies `--no-upload`.
+        #[structopt(long)]
         no_commit: bool,
     },
 }
diff --git a/llvm_tools/patch_sync/src/patch_parsing.rs b/llvm_tools/patch_sync/src/patch_parsing.rs
new file mode 100644
index 00000000..f95953f5
--- /dev/null
+++ b/llvm_tools/patch_sync/src/patch_parsing.rs
@@ -0,0 +1,199 @@
+use std::collections::{BTreeMap, BTreeSet};
+use std::fs::{copy, File};
+use std::io::{BufRead, BufReader, Read, Write};
+use std::path::{Path, PathBuf};
+
+use anyhow::{anyhow, Context, Result};
+use serde::{Deserialize, Serialize};
+use sha2::{Digest, Sha256};
+
+/// JSON serde struct.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PatchDictSchema {
+    pub rel_patch_path: String,
+    pub start_version: Option<u64>,
+    pub end_version: Option<u64>,
+    pub platforms: BTreeSet<String>,
+    pub metadata: Option<BTreeMap<String, serde_json::Value>>,
+}
+
+/// Struct to keep track of patches and their relative paths.
+#[derive(Debug, Clone)]
+pub struct PatchCollection {
+    pub patches: Vec<PatchDictSchema>,
+    pub workdir: PathBuf,
+}
+
+impl PatchCollection {
+    /// Create a `PatchCollection` from a PATCHES.
+    pub fn parse_from_file(json_file: &Path) -> Result<Self> {
+        Ok(Self {
+            patches: serde_json::from_reader(File::open(json_file)?)?,
+            workdir: json_file
+                .parent()
+                .ok_or_else(|| anyhow!("failed to get json_file parent"))?
+                .to_path_buf(),
+        })
+    }
+
+    /// Create a `PatchCollection` from a string literal and a workdir.
+    pub fn parse_from_str(workdir: PathBuf, contents: &str) -> Result<Self> {
+        Ok(Self {
+            patches: serde_json::from_str(contents)?,
+            workdir,
+        })
+    }
+
+    #[allow(dead_code)]
+    /// Return true if the collection is tracking any patches.
+    pub fn is_empty(&self) -> bool {
+        self.patches.is_empty()
+    }
+
+    /// Compute the set-set subtraction, returning a new `PatchCollection` which
+    /// keeps the minuend's wordir.
+    pub fn subtract(&self, subtrahend: &Self) -> Result<Self> {
+        let mut new_patches = Vec::new();
+        // This is O(n^2) when it could be much faster, but n is always going to be less
+        // than 1k and speed is not important here.
+        for our_patch in &self.patches {
+            let found_in_sub = subtrahend.patches.iter().any(|sub_patch| {
+                let hash1 = subtrahend
+                    .hash_from_rel_patch(sub_patch)
+                    .expect("getting hash from subtrahend patch");
+                let hash2 = self
+                    .hash_from_rel_patch(our_patch)
+                    .expect("getting hash from our patch");
+                hash1 == hash2
+            });
+            if !found_in_sub {
+                new_patches.push(our_patch.clone());
+            }
+        }
+        Ok(Self {
+            patches: new_patches,
+            workdir: self.workdir.clone(),
+        })
+    }
+
+    /// Copy all patches from this collection into another existing collection, and write that
+    /// to the existing collection's file.
+    pub fn transpose_write(&self, existing_collection: &mut Self) -> Result<()> {
+        for p in &self.patches {
+            let original_file_path = self.workdir.join(&p.rel_patch_path);
+            let copy_file_path = existing_collection.workdir.join(&p.rel_patch_path);
+            copy_create_parents(&original_file_path, &copy_file_path)?;
+            existing_collection.patches.push(p.clone());
+        }
+        existing_collection.write_patches_json("PATCHES.json")
+    }
+
+    /// Write out the patch collection contents to a PATCHES.json file.
+    fn write_patches_json(&self, filename: &str) -> Result<()> {
+        let write_path = self.workdir.join(filename);
+        let mut new_patches_file = File::create(&write_path)
+            .with_context(|| format!("writing to {}", write_path.display()))?;
+
+        let mut serialization_buffer = Vec::<u8>::new();
+        // Four spaces to indent json serialization.
+        let mut serializer = serde_json::Serializer::with_formatter(
+            &mut serialization_buffer,
+            serde_json::ser::PrettyFormatter::with_indent(b"    "),
+        );
+        self.patches
+            .serialize(&mut serializer)
+            .with_context(|| format!("Could not serialize JSON at {}", write_path.display()))?;
+        // Append a newline at the end if not present. This is necessary to get
+        // past some pre-upload hooks.
+        if serialization_buffer.last() != Some(&b'\n') {
+            serialization_buffer.push(b'\n');
+        }
+        new_patches_file.write_all(&serialization_buffer)?;
+        Ok(())
+    }
+
+    fn hash_from_rel_patch(&self, patch: &PatchDictSchema) -> Result<String> {
+        hash_from_patch_path(&self.workdir.join(&patch.rel_patch_path))
+    }
+}
+
+/// Get the hash from the patch file contents.
+///
+/// Not every patch file actually contains its own hash,
+/// we must compute the hash ourselves when it's not found.
+fn hash_from_patch(patch_contents: impl Read) -> Result<String> {
+    let mut reader = BufReader::new(patch_contents);
+    let mut buf = String::new();
+    reader.read_line(&mut buf)?;
+    let mut first_line_iter = buf.trim().split(' ').fuse();
+    let (fst_word, snd_word) = (first_line_iter.next(), first_line_iter.next());
+    if let (Some("commit" | "From"), Some(hash_str)) = (fst_word, snd_word) {
+        // If the first line starts with either "commit" or "From", the following
+        // text is almost certainly a commit hash.
+        Ok(hash_str.to_string())
+    } else {
+        // This is an annoying case where the patch isn't actually a commit.
+        // So we'll hash the entire file, and hope that's sufficient.
+        let mut hasher = Sha256::new();
+        hasher.update(&buf); // Have to hash the first line.
+        reader.read_to_string(&mut buf)?;
+        hasher.update(buf); // Hash the rest of the file.
+        let sha = hasher.finalize();
+        Ok(format!("{:x}", &sha))
+    }
+}
+
+fn hash_from_patch_path(patch: &Path) -> Result<String> {
+    let f = File::open(patch)?;
+    hash_from_patch(f)
+}
+
+/// Copy a file from one path to another, and create any parent
+/// directories along the way.
+fn copy_create_parents(from: &Path, to: &Path) -> Result<()> {
+    let to_parent = to
+        .parent()
+        .with_context(|| format!("{} has no parent", to.display()))?;
+    if !to_parent.exists() {
+        std::fs::create_dir_all(to_parent)?;
+    }
+
+    copy(&from, &to).with_context(|| {
+        format!(
+            "tried to copy file from {} to {}",
+            &from.display(),
+            &to.display()
+        )
+    })?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    /// Test we can extract the hash from patch files.
+    #[test]
+    fn test_hash_from_patch() {
+        // Example git patch from Gerrit
+        let desired_hash = "004be4037e1e9c6092323c5c9268acb3ecf9176c";
+        let test_file_contents = "commit 004be4037e1e9c6092323c5c9268acb3ecf9176c\n\
+            Author: An Author <some_email>\n\
+            Date:   Thu Aug 6 12:34:16 2020 -0700";
+        assert_eq!(
+            &hash_from_patch(test_file_contents.as_bytes()).unwrap(),
+            desired_hash
+        );
+
+        // Example git patch from upstream
+        let desired_hash = "6f85225ef3791357f9b1aa097b575b0a2b0dff48";
+        let test_file_contents = "From 6f85225ef3791357f9b1aa097b575b0a2b0dff48\n\
+            Mon Sep 17 00:00:00 2001\n\
+            From: Another Author <another_email>\n\
+            Date: Wed, 18 Aug 2021 15:03:03 -0700";
+        assert_eq!(
+            &hash_from_patch(test_file_contents.as_bytes()).unwrap(),
+            desired_hash
+        );
+    }
+}