[FIX] qweb: allow string interpolation in t-call

This commit allows the t-call directive to choose a dynamic template.
This is working in QWeb Python, but was not possible in Owl.

closes #709

doc/reference/qweb_templating_language.md

@@ -15,6 +15,7 @@
   - [Dynamic Attributes](#dynamic-attributes)
   - [Loops](#loops)
   - [Rendering Sub Templates](#rendering-sub-templates)
+  - [Dynamic Sub Templates](#dynamic-sub-templates)
   - [Translations](#translations)
   - [Debugging](#debugging)
 
@@ -509,6 +510,22 @@ This can be used to define variables scoped to a sub template:
 <!-- "var" does not exist here -->
 ```
 
+### Dynamic sub templates
+
+The `t-call` directive can also be used to dynamically call a sub template,
+using string interpolation. For example:
+
+```xml
+<div t-name="main-template">
+    <t t-call="{{template}}">
+        <em>content</em>
+    </t>
+</div>
+```
+
+Here, the name of the template is obtained from the `template` value in the
+template rendering context.
+
 ### Translations
 
 By default, QWeb specify that templates should be translated. If this behaviour

src/qweb/base_directives.ts

@@ -1,4 +1,4 @@
-import { CompilationContext } from "./compilation_context";
+import { CompilationContext, INTERP_REGEXP } from "./compilation_context";
 import { QWeb } from "./qweb";
 import { htmlToVDOM } from "../vdom/html_to_vdom";
 import { QWebVar } from "./expression_parser";
@@ -224,19 +224,35 @@ QWeb.addDirective({
     ctx.rootContext.shouldDefineScope = true;
     ctx.rootContext.shouldDefineUtils = true;
     const subTemplate = node.getAttribute("t-call")!;
+    const isDynamic = INTERP_REGEXP.test(subTemplate);
     const nodeTemplate = qweb.templates[subTemplate];
-    if (!nodeTemplate) {
+    if (!isDynamic && !nodeTemplate) {
       throw new Error(`Cannot find template "${subTemplate}" (t-call)`);
     }
 
     // Step 2: compile target template in sub templates
     // ------------------------------------------------
-    let subId = qweb.subTemplates[subTemplate];
-    if (!subId) {
-      subId = QWeb.nextId++;
-      qweb.subTemplates[subTemplate] = subId;
-      const subTemplateFn = qweb._compile(subTemplate, { hasParent: true, defineKey: true });
-      QWeb.subTemplates[subId] = subTemplateFn;
+    let subIdstr: string;
+    if (isDynamic) {
+      const _id = ctx.generateID();
+      ctx.addLine(`let tname${_id} = ${ctx.interpolate(subTemplate)};`);
+      ctx.addLine(`let tid${_id} = this.constructor.nextId++;`);
+      ctx.addIf(`!(tname${_id} in this.subTemplates)`);
+      ctx.addLine(`this.subTemplates[tname${_id}] = tid${_id};`);
+      ctx.addLine(
+        `this.constructor.subTemplates[tid${_id}] = this._compile(tname${_id}, {hasParent: true, defineKey: true});`
+      );
+      ctx.closeIf();
+      subIdstr = `tid${_id}`;
+    } else {
+      let subId = qweb.subTemplates[subTemplate];
+      if (!subId) {
+        subId = QWeb.nextId++;
+        qweb.subTemplates[subTemplate] = subId;
+        const subTemplateFn = qweb._compile(subTemplate, { hasParent: true, defineKey: true });
+        QWeb.subTemplates[subId] = subTemplateFn;
+      }
+      subIdstr = `'${subId}'`;
     }
 
     // Step 3: compile t-call body if necessary
@@ -272,12 +288,12 @@ QWeb.addDirective({
     const parentNode = ctx.parentNode ? `c${ctx.parentNode}` : "result";
     const extra = `Object.assign({}, extra, {parentNode: ${parentNode}, parent: ${parentComponent}, key: ${key}})`;
     if (ctx.parentNode) {
-      ctx.addLine(`this.constructor.subTemplates['${subId}'].call(this, scope, ${extra});`);
+      ctx.addLine(`this.constructor.subTemplates[${subIdstr}].call(this, scope, ${extra});`);
     } else {
       // this is a t-call with no parentnode, we need to extract the result
       ctx.rootContext.shouldDefineResult = true;
       ctx.addLine(`result = []`);
-      ctx.addLine(`this.constructor.subTemplates['${subId}'].call(this, scope, ${extra});`);
+      ctx.addLine(`this.constructor.subTemplates[${subIdstr}].call(this, scope, ${extra});`);
       ctx.addLine(`result = result[0]`);
     }
 

tests/qweb/__snapshots__/qweb.test.ts.snap

@@ -1391,6 +1391,54 @@ exports[`t-call (template calling cascading t-call t-raw='0' 1`] = `
 }"
 `;
 
+exports[`t-call (template calling dynamic t-call 1`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"main\\"
+    let utils = this.constructor.utils;
+    let scope = Object.create(context);
+    let h = this.h;
+    let c1 = [], p1 = {key:1};
+    let vn1 = h('div', p1, c1);
+    let tname2 = (scope['template']);
+    let tid2 = this.constructor.nextId++;
+    if (!(tname2 in this.subTemplates)) {
+        this.subTemplates[tname2] = tid2;
+        this.constructor.subTemplates[tid2] = this._compile(tname2, {hasParent: true, defineKey: true});
+    }
+    let _origScope3 = scope;
+    scope = Object.create(scope);
+    scope.__access_mode__ = 'ro';
+    this.constructor.subTemplates[tid2].call(this, scope, Object.assign({}, extra, {parentNode: c1, parent: utils.getComponent(context), key: '__4__'}));
+    scope = _origScope3;
+    return vn1;
+}"
+`;
+
+exports[`t-call (template calling dynamic t-call 2`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"main\\"
+    let utils = this.constructor.utils;
+    let scope = Object.create(context);
+    let h = this.h;
+    let c1 = [], p1 = {key:1};
+    let vn1 = h('div', p1, c1);
+    let tname2 = (scope['template']);
+    let tid2 = this.constructor.nextId++;
+    if (!(tname2 in this.subTemplates)) {
+        this.subTemplates[tname2] = tid2;
+        this.constructor.subTemplates[tid2] = this._compile(tname2, {hasParent: true, defineKey: true});
+    }
+    let _origScope3 = scope;
+    scope = Object.create(scope);
+    scope.__access_mode__ = 'ro';
+    this.constructor.subTemplates[tid2].call(this, scope, Object.assign({}, extra, {parentNode: c1, parent: utils.getComponent(context), key: '__4__'}));
+    scope = _origScope3;
+    return vn1;
+}"
+`;
+
 exports[`t-call (template calling inherit context 1`] = `
 "function anonymous(context, extra
 ) {

tests/qweb/qweb.test.ts

@@ -1095,6 +1095,16 @@ describe("t-call (template calling", () => {
     const expected = "<div><p>yip yip</p></div>";
     expect(renderToString(qweb, "main")).toBe(expected);
   });
+
+  test("dynamic t-call", () => {
+    qweb.addTemplate("foo", `<foo><t t-esc="val"/></foo>`);
+    qweb.addTemplate("bar", `<bar><t t-esc="val"/></bar>`);
+    qweb.addTemplate("main", `<div><t t-call="{{template}}"/></div>`);
+    const expected = "<div><foo>foo</foo></div>";
+    expect(renderToString(qweb, "main", { template: "foo", val: "foo" })).toBe(expected);
+    const expected2 = "<div><bar>quux</bar></div>";
+    expect(renderToString(qweb, "main", { template: "bar", val: "quux" })).toBe(expected2);
+  });
 });
 
 describe("foreach", () => {