KT-20706: Fix auto-popup completion after digit in KDoc

#KT-20706 Fixed

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/KDocCompletionContributor.kt

@@ -133,11 +133,13 @@ object KDocTagCompletionProvider : CompletionProvider<CompletionParameters>() {
     override fun addCompletions(parameters: CompletionParameters, context: ProcessingContext, result: CompletionResultSet) {
         // findIdentifierPrefix() requires identifier part characters to be a superset of identifier start characters
         val prefix = CompletionUtil.findIdentifierPrefix(
-                parameters.position.containingFile,
+            parameters.position.containingFile,
-                parameters.offset,
+            parameters.offset,
-                StandardPatterns.character().javaIdentifierPart() or singleCharPattern('@'),
+            StandardPatterns.character().javaIdentifierPart() or singleCharPattern('@'),
-                StandardPatterns.character().javaIdentifierStart() or singleCharPattern('@'))
+            StandardPatterns.character().javaIdentifierStart() or singleCharPattern('@')
+        )
 
+        if (parameters.isAutoPopup && prefix.isEmpty()) return
         if (prefix.isNotEmpty() && !prefix.startsWith('@')) {
             return
         }

idea/idea-completion/testData/kdoc/AutoPopupAfterAtInKDoc.kt

@@ -0,0 +1,8 @@
+
+/**
+ * @<caret>
+ */
+fun some() {}
+
+// INVOCATION_COUNT: 0
+// EXIST: @return

idea/idea-completion/testData/kdoc/NoAutoPopupAfterDigitInKDoc.kt

@@ -0,0 +1,8 @@
+
+/**
+ * 0<caret>
+ */
+fun some() {}
+
+// INVOCATION_COUNT: 0
+// NOTHING_ELSE

idea/idea-completion/testData/kdoc/TagName.kt

@@ -8,3 +8,4 @@ fun f(x: Int): Int {
 // EXIST: @return
 // EXIST: @suppress
 // ABSENT: @receiver
+// INVOCATION_COUNT: 1

idea/idea-completion/testData/kdoc/TagNameInClass.kt

@@ -10,3 +10,4 @@ class C<T> {
 // EXIST: @property
 // ABSENT: @return
 // ABSENT: @receiver
+// INVOCATION_COUNT: 1

idea/idea-completion/testData/kdoc/TagNameInExtensionFunction.kt

@@ -10,3 +10,4 @@ fun Int.f(): Int {
 // EXIST: @receiver
 // ABSENT: @constructor
 // ABSENT: @property
+// INVOCATION_COUNT: 1

idea/idea-completion/testData/kdoc/TagNameStart.kt

@@ -4,3 +4,4 @@ fun f(x: Int): Int {
 
 // EXIST: @param
 // EXIST: @return
+// INVOCATION_COUNT: 1

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/KDocCompletionTestGenerated.java

@@ -34,6 +34,11 @@ public class KDocCompletionTestGenerated extends AbstractJvmBasicCompletionTest
         KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/idea-completion/testData/kdoc"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
     }
 
+    @TestMetadata("AutoPopupAfterAtInKDoc.kt")
+    public void testAutoPopupAfterAtInKDoc() throws Exception {
+        runTest("idea/idea-completion/testData/kdoc/AutoPopupAfterAtInKDoc.kt");
+    }
+
     @TestMetadata("ExtensionsFQLink.kt")
     public void testExtensionsFQLink() throws Exception {
         runTest("idea/idea-completion/testData/kdoc/ExtensionsFQLink.kt");
@@ -79,6 +84,11 @@ public class KDocCompletionTestGenerated extends AbstractJvmBasicCompletionTest
         runTest("idea/idea-completion/testData/kdoc/MemberLink.kt");
     }
 
+    @TestMetadata("NoAutoPopupAfterDigitInKDoc.kt")
+    public void testNoAutoPopupAfterDigitInKDoc() throws Exception {
+        runTest("idea/idea-completion/testData/kdoc/NoAutoPopupAfterDigitInKDoc.kt");
+    }
+
     @TestMetadata("NoCompletionAfterFunName.kt")
     public void testNoCompletionAfterFunName() throws Exception {
         runTest("idea/idea-completion/testData/kdoc/NoCompletionAfterFunName.kt");

idea/src/org/jetbrains/kotlin/idea/editor/KotlinTypedHandler.java

@@ -43,6 +43,7 @@ import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.util.text.CharArrayUtil;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.KtNodeTypes;
+import org.jetbrains.kotlin.kdoc.lexer.KDocTokens;
 import org.jetbrains.kotlin.lexer.KtTokens;
 import org.jetbrains.kotlin.psi.*;
 
@@ -127,6 +128,7 @@ public class KotlinTypedHandler extends TypedHandlerDelegate {
 
             case '@':
                 autoPopupLabelLookup(project, editor);
+                autoPopupKDocTag(project, editor);
                 return Result.CONTINUE;
 
             case ':':
@@ -179,6 +181,16 @@ public class KotlinTypedHandler extends TypedHandlerDelegate {
         });
     }
 
+    private static void autoPopupKDocTag(Project project, final Editor editor) {
+        AutoPopupController.getInstance(project).autoPopupMemberLookup(editor, (PsiFile file) -> {
+            int offset = editor.getCaretModel().getOffset();
+            PsiElement lastElement = file.findElementAt(offset - 1);
+            if (lastElement == null) return false;
+
+            return lastElement.getNode().getElementType() == KDocTokens.TEXT;
+        });
+    }
+
     private static void autoPopupLabelLookup(Project project, final Editor editor) {
         AutoPopupController.getInstance(project).autoPopupMemberLookup(editor, new Condition<PsiFile>() {
             @Override