feat: auto-tail output when depends-on

src/codegen.js

@@ -0,0 +1,23 @@
+// Code generation.
+
+import text from "./text.js";
+
+const HR = text.HORIZONTAL_RULE;
+const horRules = {
+    javascript: `console.log("${HR}");`,
+    lua: `print("${HR}")`,
+    php: `echo "${HR}"`,
+    python: `print("${HR}")`,
+    r: `cat("${HR}\n")`,
+    ruby: `puts "${HR}"`,
+    typescript: `console.log("${HR}");`,
+    shell: `echo "${HR}"`,
+    sql: `select '${HR}';`,
+};
+
+// print a horizontal rule.
+function hr(syntax) {
+    return horRules[syntax] || "";
+}
+
+export default { hr };

src/output.js

@@ -28,11 +28,9 @@ template.innerHTML = `
 const builders = {
     // returns the result as a text node.
     [OutputMode.text]: (result, shouldTail) => {
-        const value = result.stdout || result.stderr || PLACEHOLDER;
-        if (shouldTail) {
-            return document.createTextNode(text.tail(value));
-        }
-        return document.createTextNode(value);
+        const value = result.stdout || result.stderr;
+        const output = shouldTail ? text.tail(value) : value;
+        return document.createTextNode(output || PLACEHOLDER);
     },
 
     // returns the result as an HTML table.

src/snippet.js

@@ -6,6 +6,7 @@ import "./output.js";
 import { EditorMode, CodeElement } from "./editor.js";
 import { Executor } from "./executor.js";
 import text from "./text.js";
+import codegen from "./codegen.js";
 
 // UI messages.
 const messages = {
@@ -269,6 +270,14 @@ class CodapiSnippet extends HTMLElement {
         this._toolbar.showStatus(message);
     }
 
+    // what syntax is used.
+    get syntax() {
+        return this.getAttribute("syntax") || this.getAttribute("sandbox");
+    }
+    set syntax(value) {
+        this.setAttribute("syntax", value);
+    }
+
     // selector is the code element css selector.
     get selector() {
         return this.getAttribute("selector");
@@ -308,12 +317,14 @@ class CodapiSnippet extends HTMLElement {
 function gatherCode(curSnip) {
     let code = curSnip.code;
     let ids = curSnip.dependsOn ? curSnip.dependsOn.split(" ") : [];
+    // print separators between snippets to tail output later
+    const sep = curSnip.hasAttribute("output-tail") ? codegen.hr(curSnip.syntax) : "";
     for (const id of ids) {
         const snip = document.getElementById(id);
         if (!snip) {
             throw new Error(`#${id} dependency not found`);
         }
-        code = snip.code + "\n" + code;
+        code = snip.code + `\n${sep}\n` + code;
         if (snip.dependsOn) {
             ids.push(...snip.dependsOn.split(" ").filter((i) => !ids.includes(i)));
         }

src/text.js

@@ -1,5 +1,6 @@
-// tail separator
-const TAIL_SEPARATOR = "---";
+// Text handling.
+
+const HORIZONTAL_RULE = "---";
 
 // cut slices s around the first instance of sep,
 // returning the text before and after sep.
@@ -15,8 +16,17 @@ function cut(s, sep) {
 // tail returns the last part of s after the separator line.
 // If s does not contain a separator, returns s unchanged.
 function tail(s) {
-    const index = s.lastIndexOf(`\n${TAIL_SEPARATOR}`);
-    return index === -1 ? s : s.slice(index + 5);
+    if (s.endsWith(HORIZONTAL_RULE)) {
+        return "";
+    }
+    const index = s.lastIndexOf(`\n${HORIZONTAL_RULE}\n`);
+    if (index !== -1) {
+        return s.slice(index + HORIZONTAL_RULE.length + 2);
+    }
+    if (s.startsWith(HORIZONTAL_RULE)) {
+        return s.slice(HORIZONTAL_RULE.length + 1);
+    }
+    return s;
 }
 
-export default { cut, tail };
+export default { cut, tail, HORIZONTAL_RULE };

tests/snippet.js

@@ -57,8 +57,9 @@ async function runTests() {
     await testOutputModeHidden();
 
     await testOutputPlaceholder();
-    await testOutputNoTail();
-    await testOutputTail();
+    await testOutputTailOff();
+    await testOutputTailOn();
+    await testOutputTailAuto();
 
     await testTemplate();
     await testTemplateChange();
@@ -763,9 +764,9 @@ async function testOutputPlaceholder() {
     });
 }
 
-async function testOutputNoTail() {
+async function testOutputTailOff() {
     return new Promise((resolve, reject) => {
-        t.log("testOutputNoTail...");
+        t.log("testOutputTailOff...");
         const ui = createSnippet(`
             <pre><code>console.log("hello");
 console.log("---");
@@ -781,9 +782,9 @@ console.log("world");</code></pre>
     });
 }
 
-async function testOutputTail() {
+async function testOutputTailOn() {
     return new Promise((resolve, reject) => {
-        t.log("testOutputTail...");
+        t.log("testOutputTailOn...");
         const ui = createSnippet(`
             <pre><code>console.log("hello");
 console.log("---");
@@ -799,6 +800,26 @@ console.log("world");</code></pre>
     });
 }
 
+async function testOutputTailAuto() {
+    return new Promise((resolve, reject) => {
+        t.log("testOutputTailAuto...");
+        const html = `
+            <pre><code>console.log("hello")</code></pre>
+            <codapi-snippet id="step-1" engine="browser" sandbox="javascript">
+            </codapi-snippet>
+            <pre><code>console.log("world")</code></pre>
+            <codapi-snippet engine="browser" sandbox="javascript" depends-on="step-1" output-tail>
+            </codapi-snippet>
+        `;
+        const ui = createSnippet(html);
+        ui.snip.addEventListener("result", (event) => {
+            t.assert("output", ui.output.out.innerHTML == "world");
+            resolve();
+        });
+        ui.toolbar.run.click();
+    });
+}
+
 async function testTemplate() {
     return new Promise((resolve, reject) => {
         t.log("testTemplate...");