srcMove is a C++ tool that post-processes srcDiff XML output and annotates detected "move" operations by adding a stable move id (and an xpath location) onto matching diff:delete / diff:insert regions.

This repository is being developed as part of a master’s thesis project focused on improving the interpretability of fine-grained source-to-source diffs produced in the srcML/srcDiff ecosystem.

Given a srcdiff.xml file (the XML produced by srcDiff), srcMove:

1. streams the XML and collects all diff:insert and diff:delete regions
2. filters the regions to choose good "move units" (default: leaf-only diff regions, skip whitespace-only, skip regions already marked with move)
3. hashes each region by its inner text content
4. groups deletes/inserts by content (hash + exact text equality confirmation)
5. assigns a new move id to each group that has both deletes and inserts
6. writes a new XML file identical to the input, except:
   • adds move="<id>" to the START tag of matched diff:insert and diff:delete
   • adds xpath="<path>" to those tags (even if move already existed)

Output is a new XML file (default: diff_new.xml) you can feed into downstream tooling, renderers, or visualizers.

• CMake 3.20+
• A C++17 compiler (Clang or GCC recommended)
• libxml2 development package
• A workspace that contains:
  • srcReader (sibling repository)
  • a built/installed srcML (expected at srcML-install)

SrcMLBuildTemplate

This project is designed to live inside a srcML workspace alongside its dependencies. While you can configure paths manually, the recommended setup is to use my installer repo, SrcMLBuildTemplate, which bootstraps a reproducible workspace.

Typical layout:

srcMLBuildTemplate/ # installer root (recommended)
 srcML/
 srcML-install/ # local srcML install prefix
 srcReader/ # dependency
 srcDiff/ # to generate input XML
 srcMove/ # this repo

From the repository root:

cmake -S . -B build \
 -G Ninja
ninja -C build

If your workspace layout differs, configure with:

cmake -S . -B build \
 -G Ninja \
 -DWORKSPACE_ROOT=/path/to/workspace \
 -DSRCREADER_ROOT=/path/to/srcReader \
 -DSRCML_INSTALL_PREFIX=/path/to/srcML-install
ninja -C build

./build/srcMove path/to/srcdiff.xml

Optionally specify an output filename:

./build/srcMove path/to/srcdiff.xml out.xml

This repo includes small, focused test fixtures under test/.

For example:

./build/srcMove test/simple/diff.xml test/simple/diff_new.xml

Or:

./build/srcMove test/function_content/diff_pos.xml test/function_content/diff_new.xml

Each test/*/ directory contains an original.cpp and modified.cpp plus diff.xml (and in many cases an example diff_new.xml) to make it easy to see what changed.

The pipeline (see src/pipeline.cpp) is intentionally simple and streaming-friendly:

• collect_all_regions (src/diff_region.*)

  • single pass over srcml_reader
  • records every diff region with nesting metadata and inner text
  • detects pre-existing move attributes and tracks the max id

• filter_regions_for_registry (src/region_filter.*)

  • selects which regions become candidates for move detection

  • defaults:

    • leaf-only diff regions
    • skip whitespace-only regions
    • skip regions that already have a move attribute

• move_registry + group builder (src/move_registry.*, src/content_groups_builder.*)

  • buckets candidates by a fast 64-bit FNV-1a hash of raw inner text
  • optionally confirms equality by exact full_text to avoid hash collisions
  • produces "content groups" that can be classified (1-to-1, many-to-many, etc.)

• annotation_plan + writer (src/writer/annotation_plan.*, src/writer/annotation_writer.*)

  • assigns a new move id per group that has both deletes and inserts
  • rewrites the XML in a second pass
  • patches only the START tags of diff:insert / diff:delete
  • writes xpath values using a streaming path builder (src/xpath_builder.*)

This design keeps memory usage predictable and avoids generating the full ×ばつI pair explosion unless explicitly requested.

srcMove edits only the START tags of diff:insert and diff:delete elements:

• move="<id>" is added only if the element was not already marked by srcDiff
• xpath="<path>" is written even if move already existed

The produced output remains valid srcDiff XML and should be usable anywhere the original was used.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<unit xmlns="http://www.srcML.org/srcML/src" xmlns:diff="http://www.srcML.org/srcDiff" revision="1.0.0" language="C++" filename="test/simple/original.cpp|test/simple/modified.cpp"><function><type><name>int</name></type> <name>main</name><parameter_list>()</parameter_list> <block>{<block_content>
<diff:delete><diff:ws> </diff:ws><diff:delete move="1" xpath="/unit[1]/function[1]/block[1]/block_content[1]/diff:delete[1]/diff:delete[1]"><decl_stmt><decl><type><name>int</name></type><diff:ws> </diff:ws><name>first</name><diff:ws> </diff:ws><init>=<diff:ws> </diff:ws><expr><literal type="number">123</literal></expr></init></decl>;</decl_stmt></diff:delete><diff:ws>
</diff:ws></diff:delete> <decl_stmt><decl><type><name>int</name></type> <name>second</name> <init>= <expr><literal type="number">456</literal></expr></init></decl>;</decl_stmt>
<diff:insert><diff:ws> </diff:ws><diff:insert move="1" xpath="/unit[1]/function[1]/block[1]/block_content[1]/diff:insert[1]/diff:insert[1]"><decl_stmt><decl><type><name>int</name></type><diff:ws> </diff:ws><name>first</name><diff:ws> </diff:ws><init>=<diff:ws> </diff:ws><expr><literal type="number">123</literal></expr></init></decl>;</decl_stmt></diff:insert><diff:ws>
</diff:ws></diff:insert> <return>return <expr><literal type="number">0</literal></expr>;</return>
</block_content>}</block></function>
</unit>

This repository also builds a few small utilities under src/tools/:

• srcdiff_render
• srcdiff_highlight
• srcdiff_highlight_pos

These are intended for debugging and inspection during development (they link against the same srcReader/srcML stack).

• src/

  • core pipeline and move detection logic

• src/tools/

  • small inspection utilities (debug-focused)

• doc/

  • diagrams, notes, terms, and papers reviewed during thesis work

• test/

  • compact fixtures (original/modified + sample diffs)

• Matching is currently content-based (raw inner text) and does not use AST-aware similarity scoring.
• Pairing is currently a fast baseline (greedy 1-to-1 consumption inside each content group).
• Many-to-many groups are identified but not fully disambiguated into specific move pairings.
• This tool expects srcDiff XML input and is not a general-purpose diff engine.

These are active areas for improvement as the thesis work progresses.

Planned directions (subject to change as research evolves):

• richer move classification (copy vs move vs repeated insertion)
• better disambiguation strategies for many-to-many groups
• scoring models that incorporate structural context (xpath, node type, surrounding tokens)
• a dedicated visualization companion tool (side-by-side view with insert/delete/move highlighting)

GPL-3.0-only. See LICENSE.

This project builds on the srcML/srcDiff tooling ecosystem and depends on srcReader and srcML for streaming parsing and writing of srcML-derived XML formats.