8254073: Tokenizer improvements (revised)

Reviewed-by: mcimadamore

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/TextBlockSupport.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.sun.tools.javac.parser;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Methods used to support text blocks lint.
+ *
+ *  <p><b>This is NOT part of any supported API.
+ *  If you write code that depends on this, you do so at your own risk.
+ *  This code and its internal interfaces are subject to change or
+ *  deletion without notice.</b>
+ */
+class TextBlockSupport {
+     enum WhitespaceChecks {
+        INCONSISTENT,
+        TRAILING
+    };
+
+    /** Check that the use of white space in content is not problematic.
+     */
+    static Set<WhitespaceChecks> checkWhitespace(String string) {
+        // Start with empty result set.
+        Set<WhitespaceChecks> checks = new HashSet<>();
+        // No need to check empty strings.
+        if (string.isEmpty()) {
+            return checks;
+        }
+        // Maximum common indentation.
+        int outdent = 0;
+        // No need to check indentation if opting out (last line is empty.)
+        char lastChar = string.charAt(string.length() - 1);
+        boolean optOut = lastChar == '\n' || lastChar == '\r';
+        // Split string based at line terminators.
+        String[] lines = string.split("\\R");
+        int length = lines.length;
+        // Extract last line.
+        String lastLine = length == 0 ? "" : lines[length - 1];
+         if (!optOut) {
+            // Prime with the last line indentation (may be blank.)
+            outdent = indexOfNonWhitespace(lastLine);
+            for (String line : lines) {
+                // Blanks lines have no influence (last line accounted for.)
+                if (!line.isBlank()) {
+                    outdent = Integer.min(outdent, indexOfNonWhitespace(line));
+                    if (outdent == 0) {
+                        break;
+                    }
+                }
+            }
+        }
+        // Last line is representative.
+        String start = lastLine.substring(0, outdent);
+        for (String line : lines) {
+            // Fail if a line does not have the same indentation.
+            if (!line.isBlank() && !line.startsWith(start)) {
+                // Mix of different white space
+                checks.add(WhitespaceChecks.INCONSISTENT);
+            }
+            // Line has content even after indent is removed.
+            if (outdent < line.length()) {
+                // Is the last character a white space.
+                lastChar = line.charAt(line.length() - 1);
+                if (Character.isWhitespace(lastChar)) {
+                    // Has trailing white space.
+                    checks.add(WhitespaceChecks.TRAILING);
+                }
+            }
+        }
+        return checks;
+    }
+
+   private static int indexOfNonWhitespace(String string) {
+        return string.length() - string.stripLeading().length();
+    }
+}