fix: keep $ on nested variables in "${...}" interpolation (#2520)

Printing `"${foo[$index_var]}"` swallowed the dollar sign of the nested
variable, producing `"${foo[index_var]}"` and silently changing semantics
(the variable becomes a bare constant). The `variable` printer dropped `$`
for any variable whose parent was an offsetlookup under a curly-simple
encapsedpart, but only the base variable of the lookup (which directly
follows the `${` emitted by the encapsedpart printer) may lose its `$`;
a variable in the offset position is nested and keeps its own `$`.

Closes #2177

Co-authored-by: Dextheking1 <Dextheking1@users.noreply.github.com>

Author: Dextheking1

src/printer.mjs

@@ -2314,6 +2314,10 @@ function printNode(path, options, print) {
           parent.curly) ||
         (parentParent &&
           parent.kind === "offsetlookup" &&
+          // Only the base variable of the lookup follows the `${` printed
+          // by the encapsedpart; a variable in the offset position is a
+          // nested variable and keeps its own `$`.
+          parent.what === node &&
           parentParent.kind === "encapsedpart" &&
           parentParent.syntax === "simple" &&
           parentParent.curly)

tests/encapsed/__snapshots__/jsfmt.spec.mjs.snap

@@ -414,6 +414,7 @@ echo "text \${foo['foo']} text";
 echo "text \${foo[foo]} text";
 echo "text \${foo[call()]} text";
 echo "text \${foo[$var ? 'foo' : 'bar']} text";
+echo "text \${foo[$index_var]} text";
 
 // T_CURLY_OPEN variable '}'
 echo "text {$var} text";
@@ -952,6 +953,7 @@ echo "text \${foo["foo"]} text";
 echo "text \${foo[foo]} text";
 echo "text \${foo[call()]} text";
 echo "text \${foo[$var ? "foo" : "bar"]} text";
+echo "text \${foo[$index_var]} text";
 
 // T_CURLY_OPEN variable '}'
 echo "text {$var} text";
@@ -1449,6 +1451,7 @@ echo "text \${foo['foo']} text";
 echo "text \${foo[foo]} text";
 echo "text \${foo[call()]} text";
 echo "text \${foo[$var ? 'foo' : 'bar']} text";
+echo "text \${foo[$index_var]} text";
 
 // T_CURLY_OPEN variable '}'
 echo "text {$var} text";
@@ -1988,6 +1991,7 @@ echo "text \${foo["foo"]} text";
 echo "text \${foo[foo]} text";
 echo "text \${foo[call()]} text";
 echo "text \${foo[$var ? "foo" : "bar"]} text";
+echo "text \${foo[$index_var]} text";
 
 // T_CURLY_OPEN variable '}'
 echo "text {$var} text";

tests/encapsed/encapsed.php

@@ -405,6 +405,7 @@ function foo1(
 echo "text ${foo[foo]} text";
 echo "text ${foo[call()]} text";
 echo "text ${foo[$var ? 'foo' : 'bar']} text";
+echo "text ${foo[$index_var]} text";
 
 // T_CURLY_OPEN variable '}'
 echo "text {$var} text";