Accept 'subgraph' form in edge parsing

Author: IvanGoncharov

src/lexer.ts

@@ -510,13 +510,9 @@ function parseGraph(lexer: Lexer): NormalizedGraph {
 
   function parseStatement(owner: NormalizedGraph | NormalizedSubgraph): void {
     // stmt: node_stmt |	edge_stmt |	attr_stmt |	ID '=' ID |	subgraph
-    if (lexer.peekIsLiteral('{')) {
-      const subgraph = owner.upsertSubgraph(null);
-      parseStatementList(subgraph);
+    if (lexer.peekIsLiteral('{') || lexer.optionalKeyword('subgraph')) {
+      const tailNodes = parseSubgraph(owner);
       if (optionalEdgeOp()) {
-        const tailNodes: NodeID[] = subgraph
-          .sortedNodes()
-          .map((node) => [node, undefined]);
         parseEdges(tailNodes, owner);
       }
       return;
@@ -547,15 +543,8 @@ function parseGraph(lexer: Lexer): NormalizedGraph {
       }
 
       case 'subgraph': {
-        const name = lexer.peekIsLiteral('{')
-          ? null
-          : lexer.expectID('subgraph name').value;
-        const subgraph = owner.upsertSubgraph(name);
-        parseStatementList(subgraph);
+        const tailNodes = parseSubgraph(owner);
         if (optionalEdgeOp()) {
-          const tailNodes: NodeID[] = subgraph
-            .sortedNodes()
-            .map((node) => [node, undefined]);
           parseEdges(tailNodes, owner);
         }
         break;
@@ -579,20 +568,27 @@ function parseGraph(lexer: Lexer): NormalizedGraph {
     }
   }
 
+  function parseSubgraph(
+    owner: NormalizedGraph | NormalizedSubgraph,
+  ): NodeID[] {
+    const name = lexer.peekIsLiteral('{')
+      ? null
+      : lexer.expectID('subgraph name').value;
+    const subgraph = owner.upsertSubgraph(name);
+    parseStatementList(subgraph);
+    return subgraph.sortedNodes().map((node) => [node, undefined]);
+  }
+
   function parseEdges(
     tailNodes: NodeID[],
     owner: NormalizedGraph | NormalizedSubgraph,
   ) {
     const newEdges = new Set<NormalizedEdge>();
     do {
-      let headNodes: NodeID[];
-      if (lexer.peekIsLiteral('{')) {
-        const subgraph = owner.upsertSubgraph(null);
-        parseStatementList(subgraph);
-        headNodes = subgraph.sortedNodes().map((node) => [node, undefined]);
-      } else {
-        headNodes = [parseNodeID(owner)];
-      }
+      const headNodes =
+        lexer.peekIsLiteral('{') || lexer.optionalKeyword('subgraph')
+          ? parseSubgraph(owner)
+          : [parseNodeID(owner)];
 
       for (const tail of tailNodes) {
         for (const head of headNodes) {

test/dot-language.test.ts

@@ -428,4 +428,38 @@ describe('Dot language support', () => {
       }
     `);
   });
+
+  it('connect nodes in subgraphs with edges', () => {
+    const result = renderString(`
+      digraph {
+        subgraph tails { a b } -> subgraph heads { c d }
+      }
+    `);
+    expectSuccessResult(result).toMatchInlineSnapshot(`
+      digraph {
+      	graph [bb="0,0,126,108"];
+      	node [label="\\N"];
+      	subgraph tails {
+      		a	[height=0.5,
+      			pos="27,90",
+      			width=0.75];
+      		b	[height=0.5,
+      			pos="99,90",
+      			width=0.75];
+      	}
+      	subgraph heads {
+      		c	[height=0.5,
+      			pos="27,18",
+      			width=0.75];
+      		d	[height=0.5,
+      			pos="99,18",
+      			width=0.75];
+      	}
+      	a -> c	[pos="e,27,36.104 27,71.697 27,64.407 27,55.726 27,47.536"];
+      	a -> d	[pos="e,84.101,33.485 41.918,74.496 51.765,64.923 64.861,52.19 76.026,41.336"];
+      	b -> c	[pos="e,41.899,33.485 84.082,74.496 74.235,64.923 61.139,52.19 49.974,41.336"];
+      	b -> d	[pos="e,99,36.104 99,71.697 99,64.407 99,55.726 99,47.536"];
+      }
+    `);
+  });
 });