From 680bcb4abb59ffbf848b30dd5740bee2a6c25550 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dominik=20Luba=C5=84ski?= <dominik.lubanski@gmail.com>
Date: Thu, 25 Jun 2020 16:48:25 +0200
Subject: [PATCH] fix(html): print pretty logs in dev environment for
 expressions

---
 src/template/core.js | 59 +++++++++++++++++++++++++++++++++++++++++++-
 test/spec/html.js    | 39 ++++++++++++++++++++++++++++-
 2 files changed, 96 insertions(+), 2 deletions(-)

diff --git a/src/template/core.js b/src/template/core.js
index bda28aeb..67a60cd8 100644
--- a/src/template/core.js
+++ b/src/template/core.js
@@ -164,6 +164,45 @@ const createWalker =
 const container = document.createElement("div");
 const styleSheetsMap = new Map();
 
+function normalizeWhitespace(input, startIndent = 0) {
+  input = input.replace(/(^[\n\s\t ]+)|([\n\s\t ]+$)+/g, "");
+
+  let i = input.indexOf("\n");
+  if (i > -1) {
+    let indent = 0 - startIndent - 2;
+    for (i += 1; input[i] === " " && i < input.length; i += 1) {
+      indent += 1;
+    }
+    return input.replace(/\n +/g, t =>
+      t.substr(0, Math.max(t.length - indent, 1)),
+    );
+  }
+
+  return input;
+}
+
+function beautifyTemplateLog(input, index) {
+  const placeholder = getPlaceholder(index);
+
+  const output = normalizeWhitespace(input)
+    .split("\n")
+    .filter(i => i)
+    .map(line => {
+      const startIndex = line.indexOf(placeholder);
+
+      if (startIndex > -1) {
+        return `| ${line}\n--${"-".repeat(startIndex)}${"^".repeat(6)}`;
+      }
+
+      return `| ${line}`;
+    })
+    .join("\n")
+    // eslint-disable-next-line no-template-curly-in-string
+    .replace(PLACEHOLDER_REGEXP_ALL, "${...}");
+
+  return `${output}`;
+}
+
 export function compileTemplate(rawParts, isSVG, styles) {
   const template = document.createElement("template");
   const parts = [];
@@ -401,7 +440,25 @@ export function compileTemplate(rawParts, isSVG, styles) {
     for (let index = 0; index < data.markers.length; index += 1) {
       const [node, marker] = data.markers[index];
       if (!prevArgs || prevArgs[index] !== args[index]) {
-        marker(host, node, args[index], prevArgs ? prevArgs[index] : undefined);
+        try {
+          marker(
+            host,
+            node,
+            args[index],
+            prevArgs ? prevArgs[index] : undefined,
+          );
+        } catch (error) {
+          if (process.env.NODE_ENV !== "production") {
+            // eslint-disable-next-line no-console
+            console.error(
+              `An error was thrown when updating a template expression:\n${beautifyTemplateLog(
+                signature,
+                index,
+              )}`,
+            );
+          }
+          throw error;
+        }
       }
     }
 
diff --git a/test/spec/html.js b/test/spec/html.js
index 391fd529..31fc6c26 100644
--- a/test/spec/html.js
+++ b/test/spec/html.js
@@ -4,6 +4,7 @@ import define from "../../src/define.js";
 import renderFactory from "../../src/render.js";
 import { dispatch, IS_IE } from "../../src/utils.js";
 import { test, resolveTimeout } from "../helpers.js";
+import { property } from "../../src/index.js";
 
 describe("html:", () => {
   let fragment;
@@ -61,7 +62,6 @@ describe("html:", () => {
   });
 
   it("throws for missing custom element in dev environment", () => {
-    window.env = "development";
     expect(() =>
       html`
         <missing-element></missing-element>
@@ -76,6 +76,7 @@ describe("html:", () => {
         <missing-element></missing-element>
       `(fragment),
     ).not.toThrow();
+    window.env = "development";
   });
 
   it("clears arguments cache when template changes", () => {
@@ -115,6 +116,42 @@ describe("html:", () => {
     });
   });
 
+  it("logs template with highlight expression when an error occur", () => {
+    define("test-html-object-property", {
+      model: property({}),
+    });
+
+    const renderWithNewLines = value => html`
+      <test-html-object-property model=${value}>
+        <div></div>
+      </test-html-object-property>
+    `;
+
+    // eslint-disable-next-line prettier/prettier
+    const renderWithoutNewLines = value => html`<test-html-object-property model=${value}></test-html-object-property>`;
+
+    spyOn(console, "error");
+
+    expect(() => {
+      renderWithNewLines(undefined)(fragment);
+    }).toThrow();
+    expect(() => {
+      renderWithoutNewLines(undefined)(fragment);
+    }).toThrow();
+
+    expect(console.error).toHaveBeenCalledTimes(2);
+
+    window.env = "production";
+
+    expect(() => {
+      renderWithoutNewLines(true)(fragment);
+    }).toThrow();
+
+    expect(console.error).toHaveBeenCalledTimes(2);
+
+    window.env = "development";
+  });
+
   describe("attribute expression with combined text value", () => {
     const render = (two, three) =>
       html`