The Settings Panel

Clash: Open Settings — the gear icon in any of the three sidebar view title bars — opens a dedicated panel titled Clash Synthesis Settings. It is a friendlier front end for the settings described in Configuration, and the only practical way to edit the Yosys scripts, since they are multi-line strings that are awkward to write in settings.json.

The panel and VS Code settings stay in sync: edits made in settings.json are reflected here as soon as the configuration changes.

Tools

A live view of the toolchain. Three tools are probed — cabal, Yosys, and nextpnr-ecp5 — each listed with:

• whether it was found,
• its version string,
• the path it resolved to,
• or the error if the probe failed,

alongside the explanation of what that tool is needed for. Refresh re-probes everything from scratch rather than reusing the cached result, which is what you want after installing a tool or changing toolCommands.

The other place-and-route binaries (nextpnr-ice40, nextpnr-himbaechel) are not in this list. They are checked on demand when Place & Route runs for their target, so this panel showing only nextpnr-ecp5 does not mean the others are missing.

This is the same information Clash: Check Toolchain reports, in a form you can leave open while fixing your environment. See Managed Toolchain for what to do about anything missing.

Elaboration

The Yosys script used by Clash: Elaborate — hierarchy and proc only, no technology mapping, producing a word-level netlist of generic cells.

The script is editable in place. A modified badge appears when it differs from the built-in default, and Reset to Default clears the override.

Synthesis

Three controls:

• Target — the FPGA family, matching synthesisTarget. Changing it switches which script the editor below is showing.
• Out-of-context — the outOfContext toggle (see Configuration). This also switches the editor, see below.
• Synthesis script — the Yosys script the next run will execute, with the same modified badge and Reset to Default button as the elaboration script.

Because each target has its own script setting, switching the dropdown and editing affects only that target. Overrides for the others are left untouched.

The editor follows the checkbox

Out-of-context synthesis runs a different script, not a variant of the target’s: it stubs the component’s sub-components as black boxes and issues no synth_* command. It is stored separately, as outOfContextScript.

So the editor is bound to whichever of the two the current settings would actually run. Tick Out-of-context and the title changes to Out-of-Context Synthesis Script, and the contents, the modified badge and the diff all switch to outOfContextScript — along with two extra placeholders, {libFiles} and {keepBlackBoxes}, that only mean anything on that path. Untick it and everything switches back to the selected target’s script. Save and Reset to Default always act on whichever is on screen.

Unsaved edits survive an unrelated settings change, but switching the target or the checkbox reloads the editor — it is bound to a different script at that point, so there is nothing for the old text to be saved to.

The Inline Diff

When a script differs from its default, the panel shows a line-by-line diff underneath the editor — added lines, removed lines, and unchanged context.

This matters more than it might sound. The default scripts do real work beyond calling synth_*: they assert the design has no unconnected or multiply-driven wires, emit the stats.json the extension parses for the sidebar, write the logic_depth.txt report, and render the diagram via show. It is easy to break one of those by accident while customising, and the diff makes it obvious what you have changed.

If a custom script drops the tee -q -o "{outputDir}/stats.json" stat -json line, synthesis fails loudly rather than silently reporting no statistics — the extension treats a missing stats.json as an error.

Remember that scripts are templates: {files}, {topModule}, {outputDir}, and {outputBaseName} are substituted before Yosys runs. {files} becomes one quoted read_verilog line per input file, so paths containing spaces are safe.