Run commands can support multiple targets

src/expressions/mapshaper-target-proxy.mjs

@@ -4,22 +4,21 @@ import { addGetters } from '../expressions/mapshaper-expression-utils';
 // import { importGeoJSON } from '../geojson/geojson-import';
 
 export function getTargetProxy(target) {
-  var lyr = target.layers[0];
-  var data = getLayerInfo(lyr, target.dataset); // layer_name, feature_count etc
-  data.layer = lyr;
-  data.dataset = target.dataset;
-  addGetters(data, {
+  var proxy = getLayerInfo(target.layer, target.dataset); // layer_name, feature_count etc
+  proxy.layer = target.layer;
+  proxy.dataset = target.dataset;
+  addGetters(proxy, {
     // export as an object, not a string or buffer
     geojson: getGeoJSON
   });
 
   function getGeoJSON() {
-    var features = exportLayerAsGeoJSON(lyr, target.dataset, {rfc7946: true}, true);
+    var features = exportLayerAsGeoJSON(target.layer, target.dataset, {rfc7946: true}, true);
     return {
       type: 'FeatureCollection',
       features: features
     };
   }
 
-  return data;
+  return proxy;
 }

src/expressions/mapshaper-template-expressions.mjs

@@ -3,15 +3,28 @@ import { getStashedVar } from '../mapshaper-stash';
 import { getTargetProxy } from '../expressions/mapshaper-target-proxy';
 import { stop, error } from '../utils/mapshaper-logging';
 import utils from '../utils/mapshaper-utils';
+import { expandCommandTargets } from '../dataset/mapshaper-target-utils';
 
 // Support for evaluating expressions embedded in curly-brace templates
 
 // Returns: a string (e.g. a command string used by the -run command)
 export async function evalTemplateExpression(expression, targets, ctx) {
   ctx = ctx || getBaseContext();
   // TODO: throw an error if target is used when there are multiple targets
-  if (targets && targets.length == 1) {
-    Object.defineProperty(ctx, 'target', {value: getTargetProxy(targets[0])});
+  if (targets) {
+    var proxies = expandCommandTargets(targets).reduce(function(memo, target) {
+      var proxy = getTargetProxy(target);
+      memo.push(proxy);
+      // index targets by layer name too
+      if (target.layer.name) {
+        memo[target.layer.name] = proxy;
+      }
+      return memo;
+    }, []);
+    Object.defineProperty(ctx, 'targets', {value: proxies});
+    if (proxies.length == 1) {
+      Object.defineProperty(ctx, 'target', {value: proxies[0]});
+    }
   }
   // Add global functions and data to the expression context
   // (e.g. functions imported via the -require command)

test/run-test.mjs

@@ -57,6 +57,23 @@ describe('mapshaper-run.js', function () {
       assert.deepEqual(JSON.parse(out['selection.json']), [{foo: 'bam'}])
     })
 
+   it('supports targets getter for multiple targets', async function() {
+      var a = {
+        type: 'LineString',
+        coordinates: [[0, 0], [1, 1]]
+      };
+      var b = {
+        type: 'LineString',
+        coordinates: [[0, 0], [2, 2]]
+      };
+      // test that targets can be referenced by name in a run expression
+      var cmd = `-i a.json b.json combine-files
+      -run '-merge-layers name={targets.a.layer_name + targets.b.layer_name}'
+      -o`;
+      var out = await api.applyCommands(cmd, {'a.json': a, 'b.json': b});
+      assert(!!out['ab.json']);
+   });
+
    it('supports io.ifile() alias', async function() {
       var data = [{foo: 'bar'}, {foo: 'baz'}, {foo: 'bam'}];
       var include = '{ \