fix(material/schematics): fix card tmpl migration (#26169)

* fixes #26038

(cherry picked from commit c8961cd)

src/material/schematics/ng-generate/mdc-migration/rules/tree-traversal.spec.ts

@@ -190,6 +190,41 @@ describe('#visitElements', () => {
     it('should add value to existing attribute that does not have a value', async () => {
       runAddAttributeTest('<a add></a>', '<a add="val"></a>');
     });
+
+    it('should handle all forms of indentation', async () => {
+      runAddAttributeTest(
+        '<a *ngFor="let item of items">',
+        '<a add="val" *ngFor="let item of items">',
+      );
+      runAddAttributeTest(
+        `
+        <a
+          *ngFor="let item of items">`,
+        `
+        <a
+          add="val"
+          *ngFor="let item of items">`,
+      );
+      runAddAttributeTest(
+        `
+        <a *ngFor="let item of items"
+        >`,
+        `
+        <a add="val" *ngFor="let item of items"
+        >`,
+      );
+      runAddAttributeTest(
+        `
+        <a
+          [attr]="
+          val">`,
+        `
+        <a
+          add="val"
+          [attr]="
+          val">`,
+      );
+    });
   });
 
   describe('remove attribute tests', () => {

src/material/schematics/ng-generate/mdc-migration/rules/tree-traversal.ts

@@ -158,19 +158,24 @@ export function updateAttribute(
   const prefix = html.slice(0, index);
   const suffix = html.slice(index);
   const attrText = newValue ? `${name}="${newValue}"` : `${name}`;
+  const indentation = parseIndentation(html, node);
+  return prefix + indentation + attrText + suffix;
+}
 
-  if (node.startSourceSpan.start.line === node.startSourceSpan.end.line) {
-    return `${prefix} ${attrText}${suffix}`;
-  }
+function parseIndentation(html: string, node: TmplAstElement): string {
+  let whitespace = '';
+  let startOffset = node.startSourceSpan.start.offset + node.name.length + 1;
 
-  const attr = node.attributes[0];
-  if (attr) {
-    const ctx = attr.sourceSpan.start.getContext(attr.sourceSpan.start.col + 1, 1)!;
-    const indentation = ctx.before;
-    return prefix + indentation + attrText + suffix;
-  }
+  // Starting after the start source span's tagname,
+  // read and store each char until we reach a non-whitespace char.
 
-  return prefix + attrText + suffix;
+  for (let i = startOffset; i < node.startSourceSpan.end.offset - 1; i++) {
+    if (!/\s/.test(html.charAt(i))) {
+      break;
+    }
+    whitespace += html.charAt(i);
+  }
+  return whitespace || ' ';
 }
 
 /**