Program Slicing — Engineering Design

Backward and forward program slices over a function’s PDG: the minimal set of statements that affect (or are affected by) a variable at a given source line.

Program Slicing tab — source editor and slice controls (gbuilder)

Figure 1: Program Slicing tab — function picker, line/variable/direction inputs, and CodeMirror source view with highlighted slice lines.

1. Goals

Goal	How
Minimal relevant code	PDG traversal from slice criterion
CLI automation	`rgctl slice FILE --line N --variable V`
Dashboard exploration	WASM `compute_slice` on exported PDG bundles
Security cross-check	`--taint` mode shares taint engine paths

Requires discover --with-cfg (and --with-taint for discover-time taint) for PDG archives and dashboard export.

2. Architecture overview

flowchart LR
  subgraph discover["discover --with-cfg"]
    CFG[CFG per function]
    PDG[PDG per function]
    ARC[cfg_pdg.archive.bin]
    CFG --> PDG --> ARC
  end

  subgraph export["Dashboard export"]
    SI[slice_index.json]
    SB[slice/*.json]
    ARC --> SI
    ARC --> SB
  end

  subgraph runtime["Query"]
    CLI[slice CLI — reads source + PDG]
    WASM[worker compute_slice]
    CLI --> PDG
    WASM --> SB
  end

3. Slice criterion

Field	Role
`file`	Source path (read from disk at CLI; bundled in dashboard)
`--line`	1-based line number
`--variable`	Variable name at criterion
`--function`	Enclosing method name (disambiguation)
`--direction`	`backward` (default) or `forward`

4. Rust implementation map

Component	Path
CFG construction	`crates/rgctl-analysis/src/cfg.rs`
PDG + slicing	`crates/rgctl-analysis/src/pdg.rs`, `slicing.rs`
CLI	`src/cli/slice.rs`
Archive storage	`crates/rgctl-analysis/src/storage.rs`
Dashboard export	`crates/rgctl-dashboard/src/slice_export.rs`

5. Dashboard implementation

Piece	Path
Tab	`dashboard/src/SliceView.tsx`
Editor	`dashboard/src/sliceEditor.tsx` (CodeMirror)
Worker	`computeSlice(functionId, line, variable, direction)`
Index	`slice_index.json` → `slice/{uuid}.json`

6. CLI usage

rgctl discover . --cfg
rgctl slice src/Foo.java --line 42 --variable cart --function checkOut
rgctl -f json slice src/Foo.java --line 10 --variable req --direction forward
rgctl slice src/Foo.java --line 8 --variable input --taint

7. Testing

Layer	Location
Analysis unit tests	`crates/rgctl-analysis/src/slicing.rs`
CLI subprocess	`tests/cli_output/all_commands_sanity.rs`
Dashboard harness	`tests/dashboard_harness.rs` (`slice_index.json`)

Screenshots: capture-design-screenshots.mjs → docs/images/design/program-slicing/.