README.md

lsp-demo

This demo is a small library-loans module to open in an editor that runs jscpd --lsp. Clones are on by default, and the lsp section of its .jscpd.json turns on three more analyses: similar functions (ast), dead code and complexity. Each file then shows what one of them reports. The setup for each editor is in docs/editors.md.

Run the commands from this directory, so that the demo's own .jscpd.json is the config. The numbers below come from the defaults (--min-tokens 50, --min-lines 5).

File	What it holds	Diagnostic
src/loans.js	daysLate, copied into holds.js	jscpd/duplicate-code on line 4
	renewalsLeft, built like holdsAhead in holds.js	jscpd/similar-function on line 13
	loanStatus, with 19 branches	jscpd/complex-function on line 22
src/holds.js	the other copy of daysLate, and holdsAhead	the same clone and pair, seen from this side
src/index.js	an import of padLeft that nothing uses	unused-import on line 3, faded
src/format.js	formatFine, which no file imports	unused-export on line 7, faded

In headless Neovim

This prints what the server publishes for one file. It needs Neovim 0.10 or later and jscpd on the PATH:

cd fixtures/lsp-demo
nvim --headless --clean src/loans.js \
  -c "lua vim.lsp.start({ name = 'jscpd', cmd = { 'jscpd', '--lsp' }, root_dir = vim.fn.getcwd() })" \
  -c "lua vim.wait(3000)" \
  -c "lua for _, d in ipairs(vim.diagnostic.get(0)) do print(d.lnum + 1, d.code, d.message) end" \
  -c "qa!"

4 jscpd/duplicate-code Duplicated in src/holds.js:4-13 (80 tokens)
13 jscpd/similar-function Same structure as the function at src/holds.js:13-20 (1.00)
22 jscpd/complex-function Complexity 20 in loanStatus, over the limit of 15

With src/index.js and src/format.js in place of src/loans.js, the same command prints the dead code:

3 unused-import `padLeft` is imported but never used (100%)

7 unused-export exported function `formatFine` is never imported (85%)

The clone runs from line 4 to line 13 because it takes in the export function that opens the next function in both files. Edit daysLate in one of the files in the editor, and the clone diagnostic goes away before you save.

The same findings from the command line

Each analysis of the server is a mode of the CLI:

jscpd .                   # Found 1 clones.
jscpd --similarity 0.85 . # Found 2 clones. (the second is similar (ast) ~1.00)
jscpd --dead-code .       # Found 2 dead code findings in 4 files (4.6% of 87 lines).
jscpd --complexity .      # src/loans.js first, at CX 27 for the whole file

The server counts complexity per function as well, which is why loanStatus gets a diagnostic of its own at CX 20.

Semantic clones

The demo leaves the semantic analysis off, since it needs the embedding model. To try it, download the model once and add "semantic": { "enabled": true } to the lsp section:

jscpd --semantic-download

The first run embeds every function in the background, and the editor shows its progress.