[Canvas] Feat: make an empty pipeline expression legal (#28796)

packages/kbn-interpreter/src/common/lib/ast.from_expression.test.js

@@ -22,17 +22,21 @@ import { getType } from './get_type';
 
 describe('ast fromExpression', () => {
   describe('invalid expression', () => {
-    it('throws when empty', () => {
-      const check = () => fromExpression('');
-      expect(check).toThrowError(/Unable to parse expression/i);
-    });
-
     it('throws with invalid expression', () => {
       const check = () => fromExpression('wat!');
       expect(check).toThrowError(/Unable to parse expression/i);
     });
   });
 
+  describe('zero-item expression', () => {
+    it('yields a zero-length chain when empty', () => {
+      const expression = '';
+      const astObject = fromExpression(expression);
+      expect(astObject).toHaveProperty('chain');
+      expect(astObject.chain).toEqual([]);
+    });
+  });
+
   describe('single item expression', () => {
     it('is a chain', () => {
       const expression = 'whatever';

packages/kbn-interpreter/src/common/lib/grammar.js

@@ -147,7 +147,7 @@ function peg$parse(input, options) {
       peg$c3 = function(first, rest) {
           return addMeta({
             type: 'expression',
-            chain: [first].concat(rest)
+            chain: first ? [first].concat(rest) : []
           }, text(), location());
         },
       peg$c4 = peg$otherExpectation("function"),
@@ -364,6 +364,9 @@ function peg$parse(input, options) {
     }
     if (s1 !== peg$FAILED) {
       s2 = peg$parsefunction();
+      if (s2 === peg$FAILED) {
+        s2 = null;
+      }
       if (s2 !== peg$FAILED) {
         s3 = [];
         s4 = peg$currPos;

packages/kbn-interpreter/src/common/lib/grammar.peg

@@ -5,6 +5,9 @@
 * Yes, technically you can load this and build the parser in real time, but this makes it annoying
 * to share the grammar between the front end and back, so, you know, just generate the parser.
 * You shouldn't be futzing around in the grammar very often anyway.
+*
+* Instructions for generating `grammar.json`: https://github.com/elastic/kibana/issues/28776#issue-399489673
+*
 */
 
 {
@@ -20,10 +23,10 @@ start
   = expression
 
 expression
-  = space? first:function rest:('|' space? fn:function { return fn; })* {
+  = space? first:function? rest:('|' space? fn:function { return fn; })* {
     return addMeta({
       type: 'expression',
-      chain: [first].concat(rest)
+      chain: first ? [first].concat(rest) : []
     }, text(), location());
   }
 

src/legacy/core_plugins/interpreter/common/interpreter/interpret.js

@@ -145,7 +145,7 @@ export function interpreterProvider(config) {
     const argAstsWithDefaults = reduce(
       argDefs,
       (argAsts, argDef, argName) => {
-        if (typeof argAsts[argName] === 'undefined' && typeof argDef.default !== 'undefined')  {
+        if (typeof argAsts[argName] === 'undefined' && typeof argDef.default !== 'undefined') {
           argAsts[argName] = [fromExpression(argDef.default, 'argument')];
         }
 

x-pack/plugins/canvas/canvas_plugin_src/renderers/time_filter/index.js

@@ -16,16 +16,18 @@ export const timeFilter = () => ({
   help: 'Set a time window',
   reuseDomNode: true, // must be true, otherwise filters get reset when re-rendered
   render(domNode, config, handlers) {
-    const ast = fromExpression(handlers.getFilter());
-
-    // Check if the current column is what we expect it to be. If the user changes column this will be called again,
-    // but we don't want to run setFilter() unless we have to because it will cause a data refresh
-    const column = get(ast, 'chain[0].arguments.column[0]');
-    if (column !== config.column) {
-      set(ast, 'chain[0].arguments.column[0]', config.column);
-      handlers.setFilter(toExpression(ast));
+    const filterExpression = handlers.getFilter();
+    const filterExists = filterExpression !== '';
+    const ast = fromExpression(filterExpression);
+    if (filterExists) {
+      // Check if the current column is what we expect it to be. If the user changes column this will be called again,
+      // but we don't want to run setFilter() unless we have to because it will cause a data refresh
+      const column = get(ast, 'chain[0].arguments.column[0]');
+      if (column !== config.column) {
+        set(ast, 'chain[0].arguments.column[0]', config.column);
+        handlers.setFilter(toExpression(ast));
+      }
     }
-
     ReactDOM.render(
       <TimeFilter
         compact={config.compact}

x-pack/plugins/canvas/public/components/debug/debug.js

@@ -14,5 +14,5 @@ export const Debug = ({ payload }) => (
 );
 
 Debug.propTypes = {
-  payload: PropTypes.object.isRequired,
+  payload: PropTypes.object,
 };

x-pack/plugins/canvas/public/components/render_with_fn/render_with_fn.js

@@ -25,7 +25,7 @@ export class RenderWithFn extends React.Component {
       destroy: PropTypes.func.isRequired,
       onDestroy: PropTypes.func.isRequired,
     }),
-    config: PropTypes.object.isRequired,
+    config: PropTypes.object,
     size: PropTypes.object.isRequired,
     onError: PropTypes.func.isRequired,
   };