Prompt API: Reject system messages appended after others

Reject appending system messages when sessions have [pending] context.
Run ValidateInput on prompt and append; track imminent pending usage.
Update exception message. Add WPT coverage.

Fixed: 495843316
Change-Id: I77dfb450719e86041c3e1ebea83f0511c3db4e43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7698599
Auto-Submit: Mike Wasserman <msw@chromium.org>
Commit-Queue: Mike Wasserman <msw@chromium.org>
Reviewed-by: Jingyun Liu <jingyun@google.com>
Cr-Commit-Position: refs/heads/main@{#1605041}

Author: Mike Wasserman

ai/language-model/language-model-append.tentative.https.window.js

@@ -42,3 +42,24 @@ promise_test(async t => {
   await promise_rejects_quotaexceedederror(
       t, session.append(promptString), usage, session.contextWindow);
 }, 'Test that append input exceeding the total context window rejects');
+
+promise_test(async t => {
+  await ensureLanguageModel();
+  const session = await createLanguageModel();
+  const result1 = session.append([
+    {role: 'user', content: 'foo'},
+    {role: 'system', content: 'bar'},
+  ]);
+  await promise_rejects_js(t, TypeError, result1);
+
+  const result2 = session.append([
+    {role: 'system', content: 'foo'},
+    {role: 'system', content: 'bar'},
+  ]);
+  await promise_rejects_js(t, TypeError, result2);
+
+  const result3 = session.append({role: 'system', content: 'foo'});
+  await promise_rejects_js(
+      t, TypeError, session.append([{role: 'system', content: 'bar'}]));
+  await result3;
+}, 'append() should reject system role messages after other messages');

ai/language-model/language-model-create.tentative.https.window.js

@@ -70,13 +70,19 @@ promise_test(async t => {
 }, 'Create with initialPrompts without system role');
 
 promise_test(async t => {
-  let result = createLanguageModel({
+  let result1 = createLanguageModel({
     initialPrompts: [
       {role: 'user', content: 'hello'}, {role: 'assistant', content: 'hello'},
       {role: 'system', content: 'you are a robot'}
     ]
   });
-  await promise_rejects_js(t, TypeError, result);
+  await promise_rejects_js(t, TypeError, result1);
+
+  let result2 = createLanguageModel({
+    initialPrompts:
+        [{role: 'system', content: 'foo'}, {role: 'system', content: 'bar'}]
+  });
+  await promise_rejects_js(t, TypeError, result2);
 }, 'Create with system role not ordered first should fail');
 
 promise_test(async t => {

ai/language-model/language-model-measure-context-usage.tentative.https.window.js

@@ -8,14 +8,21 @@
 
 promise_test(async t => {
   await ensureLanguageModel();
-
-  // Start a new session.
   const session = await createLanguageModel();
+  const result = await session.measureContextUsage('This is a prompt.');
+  assert_equals(typeof result, 'number');
+  assert_greater_than(result, 0);
+}, 'measureContextUsage returns a number greater than zero for text');
 
-  // Test the measureContextUsage() API.
-  let result = await session.measureContextUsage('This is a prompt.');
-  assert_true(
-    typeof result === "number" && result > 0,
-    "The counting result should be a positive number."
-  );
-});
+promise_test(async t => {
+  const prompts = [
+    {role: 'system', content: 'foo'},
+    {role: 'user', content: 'bar'},
+    {role: 'assistant', content: 'baz'},
+  ];
+  await ensureLanguageModel();
+  const session = await createLanguageModel({initialPrompts: prompts});
+  const result = await session.measureContextUsage(prompts);
+  assert_equals(typeof result, 'number');
+  assert_greater_than(result, 0);
+}, 'measure message sequences of various roles, even after adding prompts');

ai/language-model/language-model-prompt.tentative.https.window.js

@@ -42,15 +42,15 @@ promise_test(async (t) => {
 promise_test(async () => {
   const options = {
     initialPrompts:
-        [{role: 'system', content: [{type: 'text', value: 'The word of the day is regurgitation.'}]}]
+        [{role: 'system', content: 'The word of the day is regurgitation.'}]
   };
   await ensureLanguageModel(options);
   const session = await LanguageModel.create(options);
   const usage = await session.measureContextUsage(options.initialPrompts);
   assert_greater_than(usage, 0);
   assert_equals(session.contextUsage, usage);
-  assert_regexp_match(await session.prompt('What is the word of the day?'),
-                      /regurgitation/i);
+  assert_regexp_match(
+      await session.prompt('What is the word of the day?'), /regurgitation/i);
 }, 'Test that initialPrompt counts towards session contextUsage');
 
 promise_test(async () => {
@@ -80,3 +80,24 @@ promise_test(async t => {
   await promise_rejects_quotaexceedederror(
       t, session.prompt(promptString), usage, session.contextWindow);
 }, 'Test that prompt input exceeding the total context window rejects');
+
+promise_test(async t => {
+  await ensureLanguageModel();
+  const session = await createLanguageModel();
+  const result1 = session.prompt([
+    {role: 'user', content: 'foo'},
+    {role: 'system', content: 'bar'},
+  ]);
+  await promise_rejects_js(t, TypeError, result1);
+
+  const result2 = session.prompt([
+    {role: 'system', content: 'foo'},
+    {role: 'system', content: 'bar'},
+  ]);
+  await promise_rejects_js(t, TypeError, result2);
+
+  const result3 = session.prompt({role: 'system', content: 'foo'});
+  await promise_rejects_js(
+      t, TypeError, session.prompt([{role: 'system', content: 'bar'}]));
+  await result3;
+}, 'prompt() should reject system role messages after other messages');