indent: ignored nodes should accept any indentation

When a node is ignored by the indent rule, it ought not to matter
how it’s indented. But the ignoring of nodes was implemented in
such a way that the *type* of indentation (tabs vs spaces) was
being checked. For example in "tab" mode, an ignored line indented
by four spaces would cause the error “Expected indentation of 4 tabs
but found 4 spaces”.

In particular, this is a problem with “tabs for indentation, spaces
for alignment” styles, where we want to allow code like:

var x = 1,
    y = 2;

where the second line is aligned using four spaces.

This commit marks ignored indents by making them instances of
the IgnoredTokenIndent class, and explicitly ignoring the indentation
of such lines.

All tests pass.

Fixes eslint#9392.

lib/rules/indent.js

@@ -227,6 +227,27 @@ class TokenInfo {
     }
 }
 
+/**
+ * A class to store information on a token we are ignoring
+ */
+class IgnoredTokenIndent {
+
+    /**
+     * @param {number} indent The observed indent
+     */
+    constructor(indent) {
+        this._indent = indent;
+    }
+
+    /**
+     * @returns {number} The indent
+     */
+    valueOf() {
+        return this._indent;
+    }
+}
+
+
 /**
  * A class to store information on desired offsets of tokens from each other
  */
@@ -415,9 +436,10 @@ class OffsetStorage {
 
             if (this._ignoredTokens.has(token)) {
 
-                // If the token is ignored, use the actual indent of the token as the desired indent.
-                // This ensures that no errors are reported for this token.
-                this._desiredIndentCache.set(token, this._tokenInfo.getTokenIndent(token).length / this._indentSize);
+                // If the token is ignored, set the desired indent to an IgnoredTokenIndent
+                const observedIndent = this._tokenInfo.getTokenIndent(token).length / this._indentSize;
+
+                this._desiredIndentCache.set(token, new IgnoredTokenIndent(observedIndent));
             } else if (this._lockedFirstTokens.has(token)) {
                 const firstToken = this._lockedFirstTokens.get(token);
 
@@ -722,6 +744,10 @@ module.exports = {
          * @returns {boolean} `true` if the token's indentation is correct
          */
         function validateTokenIndent(token, desiredIndentLevel) {
+            if (desiredIndentLevel instanceof IgnoredTokenIndent) {
+                return true;
+            }
+
             const indentation = tokenInfo.getTokenIndent(token);
             const expectedChar = indentType === "space" ? " " : "\t";
 

tests/lib/rules/indent.js

@@ -4744,6 +4744,23 @@ ruleTester.run("indent", rule, {
                 </foo>
             `,
             options: [4, { ignoredNodes: ["JSXOpeningElement"] }]
+        },
+        {
+            code: unIndent`
+                {
+                \tvar x = 1,
+                \t    y = 2;
+                }
+            `,
+            options: ["tab"]
+        },
+        {
+            code: unIndent`
+                var x = 1,
+                    y = 2;
+                var z;
+            `,
+            options: ["tab", { ignoredNodes: ["VariableDeclarator"] }]
         }
     ],