function activateDecorations()

in src/extension/index.ts [143:200]
54 lines of code
7 McCabe index (conditional complexity)

function activateDecorations(disposables: Disposable[], store: Store) {
    const decorationTypeCallout = window.createTextEditorDecorationType({
        after: { color: new ThemeColor('problemsWarningIcon.foreground') }
    });
    const decorationTypeHighlight = window.createTextEditorDecorationType({
        border: '1px',
        borderStyle: 'solid',
        borderColor: new ThemeColor('problemsWarningIcon.foreground'),
    });
    disposables.push(languages.registerCodeActionsProvider('*', {
        provideCodeActions: (doc, _range, context) => {
            if (context.only) return;

            const diagnostic = context.diagnostics[0] as ResultDiagnostic | undefined;
            if (!diagnostic) return;

            const result = diagnostic?.result;
            if (!result) return; // Don't clear the decorations until the next result is selected.

            const editor = window.visibleTextEditors.find(editor => editor.document === doc);
            if (!editor) return; // When would editor be undef?

            const locations = result.codeFlows?.[0]?.threadFlows?.[0]?.locations ?? [];
            const messages = locations.map((tfl, i) => {
                const text = tfl.location?.message?.text;
                return `Step ${i + 1}${text ? `: ${text}` : ''}`;
            });
            const ranges = locations.map(tfl => regionToSelection(doc, tfl.location?.physicalLocation?.region));
            const rangesEnd = ranges.map(range => {
                const endPos = doc.lineAt(range.end.line).range.end;
                return new Range(endPos, endPos);
            });
            const rangesEndAdj = rangesEnd.map(range => {
                const tabCount = doc.lineAt(range.end.line).text.match(/\t/g)?.length ?? 0;
                const tabCharAdj = tabCount * (editor.options.tabSize as number - 1); // Intra-character tabs are counted wrong.
                return range.end.character + tabCharAdj;
            });
            const maxRangeEnd = Math.max(...rangesEndAdj) + 2; // + for Padding
            const decorCallouts = rangesEnd.map((range, i) => ({
                range,
                hoverMessage: messages[i],
                renderOptions: { after: { contentText: ` ${'┄'.repeat(maxRangeEnd - rangesEndAdj[i])} ${messages[i]}`, } }, // ←
            }));
            editor.setDecorations(decorationTypeCallout, decorCallouts);
            editor.setDecorations(decorationTypeHighlight, ranges);
            return [];
        }
    }));
    const disposer = observe(store.logs, change => {
        const {removed} = change as unknown as IArraySplice<Log>;
        if (!removed.length) return;
        window.visibleTextEditors.forEach(editor => {
            editor.setDecorations(decorationTypeCallout, []);
            editor.setDecorations(decorationTypeHighlight, []);
        });
    });
    disposables.push({ dispose: disposer });
}