[FIX] compiler: fix falsy values for properties not keeping input empty

Recently, we made it so that when a component is rendered, it always
updates the property values for computed properties. This was done by
wrapping the value in a String or Boolean object. One issue with this is
that wrapping a falsy value in a String doesn't yield an empty string,
but a string containing the value as text (eg new String(undefined) ->
"undefined"), which causes the value to not remain empty as per the
spec. This commit fixes that by adding a fallback to the empty string
for falsy values before converting to a String object.

closes: #1236

src/compiler/code_generator.ts

@@ -584,8 +584,12 @@ export class CodeGenerator {
         expr = compileExpr(ast.attrs[key]);
         if (attrName && isProp(ast.tag, attrName)) {
           // we force a new string or new boolean to bypass the equality check in blockdom when patching same value
-          const C = attrName === "value" ? "String" : "Boolean";
+          if (attrName === "value") {
-          expr = `new ${C}(${expr})`;
+            // When the expression is falsy, fall back to an empty string
+            expr = `new String((${expr}) || "")`;
+          } else {
+            expr = `new Boolean(${expr})`;
+          }
         }
         const idx = block!.insertData(expr, "attr");
         if (key === "t-att") {

tests/compiler/__snapshots__/attributes.test.ts.snap

@@ -708,6 +708,20 @@ exports[`attributes updating classes (with obj notation) 1`] = `
 }"
 `;
 
+exports[`attributes updating property with falsy value 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  let block1 = createBlock(\`<input block-attribute-0=\\"value\\"/>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    let attr1 = new String((ctx['v']) || \\"\\");
+    return block1([attr1]);
+  }
+}"
+`;
+
 exports[`attributes various escapes 1`] = `
 "function anonymous(app, bdom, helpers
 ) {
@@ -773,7 +787,7 @@ exports[`special cases for some specific html attributes/properties input with t
   let block1 = createBlock(\`<input block-attribute-0=\\"value\\"/>\`);
   
   return function template(ctx, node, key = \\"\\") {
-    let attr1 = new String(ctx['v']);
+    let attr1 = new String((ctx['v']) || \\"\\");
     return block1([attr1]);
   }
 }"
@@ -787,7 +801,7 @@ exports[`special cases for some specific html attributes/properties input with t
   let block1 = createBlock(\`<input block-attribute-0=\\"value\\"/>\`);
   
   return function template(ctx, node, key = \\"\\") {
-    let attr1 = new String(ctx['v']);
+    let attr1 = new String((ctx['v']) || \\"\\");
     return block1([attr1]);
   }
 }"
@@ -815,7 +829,7 @@ exports[`special cases for some specific html attributes/properties select with
   let block1 = createBlock(\`<select block-attribute-0=\\"value\\"><option value=\\"potato\\">Potato</option><option value=\\"tomato\\">Tomato</option><option value=\\"onion\\">Onion</option></select>\`);
   
   return function template(ctx, node, key = \\"\\") {
-    let attr1 = new String(ctx['value']);
+    let attr1 = new String((ctx['value']) || \\"\\");
     return block1([attr1]);
   }
 }"
@@ -829,7 +843,7 @@ exports[`special cases for some specific html attributes/properties textarea wit
   let block1 = createBlock(\`<textarea block-attribute-0=\\"value\\"/>\`);
   
   return function template(ctx, node, key = \\"\\") {
-    let attr1 = new String(ctx['v']);
+    let attr1 = new String((ctx['v']) || \\"\\");
     return block1([attr1]);
   }
 }"

tests/compiler/__snapshots__/misc.test.ts.snap

@@ -277,7 +277,7 @@ exports[`misc other complex template 1`] = `
       const b15 = list(c_block15);
       b14 = block14([], [b15]);
     }
-    let attr8 = new String(ctx['search'].value);
+    let attr8 = new String((ctx['search'].value) || \\"\\");
     let hdlr4 = [ctx['updateFilter'], ctx];
     let hdlr5 = [ctx['updateFilter'], ctx];
     let hdlr6 = [ctx['clearSearch'], ctx];

tests/compiler/attributes.test.ts

@@ -329,6 +329,35 @@ describe("attributes", () => {
     expect(fixture.innerHTML).toBe('<div value=""></div>');
   });
 
+  test("updating property with falsy value", async () => {
+    // render input with initial value
+    const template = `<input t-att-value="v"></input>`;
+    const bnode1 = renderToBdom(template, { v: false });
+    const fixture = makeTestFixture();
+    mount(bnode1, fixture);
+
+    const input = fixture.querySelector("input")!;
+    expect(input.value).toBe("");
+
+    patch(bnode1, renderToBdom(template, { v: "owl" }));
+    expect(input.value).toBe("owl");
+
+    patch(bnode1, renderToBdom(template, { v: false }));
+    expect(input.value).toBe("");
+
+    patch(bnode1, renderToBdom(template, { v: "owl" }));
+    expect(input.value).toBe("owl");
+
+    patch(bnode1, renderToBdom(template, { v: undefined }));
+    expect(input.value).toBe("");
+
+    patch(bnode1, renderToBdom(template, { v: "owl" }));
+    expect(input.value).toBe("owl");
+
+    patch(bnode1, renderToBdom(template, { v: null }));
+    expect(input.value).toBe("");
+  });
+
   test("changing a class with t-att-class", () => {
     // render input with initial value
     const template = `<div t-att-class="v"/>`;