Warning for negative string offset (< PHP 7.1)

.gitignore

@@ -15,3 +15,4 @@ all_output.*
 .phan/config.local.php
 nohup.out
 *.md.new
+.idea/

src/Phan/AST/UnionTypeVisitor.php

@@ -1193,6 +1193,7 @@ public function visitDim(Node $node) : UnionType
         static $string_type;
         static $int_union_type;
         static $int_or_string_union_type;
+
         if ($array_access_type === null) {
             // array offsets work on strings, unfortunately
             // Double check that any classes in the type don't
@@ -1206,12 +1207,14 @@ public function visitDim(Node $node) : UnionType
             $int_union_type = IntType::instance(false)->asUnionType();
             $int_or_string_union_type = new UnionType([IntType::instance(false), StringType::instance(false)], true);
         }
+
         if ($union_type->hasTopLevelArrayShapeTypeInstances()) {
             $element_type = $this->resolveArrayShapeElementTypes($node, $union_type);
             if ($element_type !== null) {
                 return $element_type;
             }
         }
+
         $dim_type = self::unionTypeFromNode(
             $this->code_base,
             $this->context,
@@ -1221,12 +1224,11 @@ public function visitDim(Node $node) : UnionType
 
         // Figure out what the types of accessed array
         // elements would be.
-        $generic_types =
-            $union_type->genericArrayElementTypes();
+        $generic_types = $union_type->genericArrayElementTypes();
 
         // If we have generics, we're all set
         if (!$generic_types->isEmpty()) {
-            if ($this->isSuspiciousNullable($union_type) && !($node->flags & self::FLAG_IGNORE_NULLABLE)) {
+            if (!($node->flags & self::FLAG_IGNORE_NULLABLE) && $this->isSuspiciousNullable($union_type)) {
                 $this->emitIssue(
                     Issue::TypeArraySuspiciousNullable,
                     $node->lineno ?? 0,
@@ -1235,7 +1237,8 @@ public function visitDim(Node $node) : UnionType
             }
 
             if (!$dim_type->isEmpty()) {
-                if (!$union_type->asExpandedTypes($this->code_base)->hasArrayAccess() && !$union_type->hasMixedType()) {
+                if (!$union_type->hasMixedType() && !$union_type->asExpandedTypes($this->code_base)->hasArrayAccess()) {
+
                     if (Config::getValue('scalar_array_key_cast')) {
                         $expected_key_type = $int_or_string_union_type;
                     } else {
@@ -1244,14 +1247,14 @@ public function visitDim(Node $node) : UnionType
                             GenericArrayType::CONVERT_KEY_MIXED_TO_INT_OR_STRING_UNION_TYPE
                         );
                     }
+
                     if (!$dim_type->canCastToUnionType($expected_key_type)) {
                         $issue_type = Issue::TypeMismatchDimFetch;
 
-                        if ($dim_type->containsNullable()) {
-                            if ($dim_type->nonNullableClone()->canCastToUnionType($expected_key_type)) {
-                                $issue_type = Issue::TypeMismatchDimFetchNullable;
-                            }
+                        if ($dim_type->containsNullable() && $dim_type->nonNullableClone()->canCastToUnionType($expected_key_type)) {
+                            $issue_type = Issue::TypeMismatchDimFetchNullable;
                         }
+
                         if ($this->should_catch_issue_exception) {
                             $this->emitIssue(
                                 $issue_type,
@@ -1262,6 +1265,7 @@ public function visitDim(Node $node) : UnionType
                             );
                             return $generic_types;
                         }
+
                         throw new IssueException(
                             Issue::fromType($issue_type)(
                                 $this->context->getFile(),
@@ -1289,6 +1293,10 @@ public function visitDim(Node $node) : UnionType
         if ($union_type->isType($string_type)
             || ($union_type->canCastToUnionType($string_type->asUnionType()) && !$union_type->hasMixedType())
         ) {
+            if (Config::get_closest_target_php_version_id() < 70100 && $union_type->isNonNullStringType()) {
+               $this->analyzeNegativeStringOffsetCompatibility($node);
+            }
+
             if (!$dim_type->isEmpty() && !$dim_type->canCastToUnionType($int_union_type)) {
                 // TODO: Efficient implementation of asExpandedTypes()->hasArrayAccess()?
                 if (!$union_type->isEmpty() && !$union_type->asExpandedTypes($this->code_base)->hasArrayLike()) {
@@ -2817,4 +2825,21 @@ public static function anyStringLiteralForNode(
         }
         return null;
     }
+
+    /**
+     * @param Node $node
+     */
+    private function analyzeNegativeStringOffsetCompatibility(Node $node)
+    {
+        if (($node->children['dim'] ?? null) instanceof Node
+            && $node->children['dim']->kind === \ast\AST_UNARY_OP
+            && $node->children['dim']->flags === \ast\flags\UNARY_MINUS
+            && \is_int($node->children['dim']->children['expr'] ?? null)
+        ) {
+            $this->emitIssue(
+                Issue::CompatibleNegativeStringOffset,
+                $node->lineno ?? 0
+            );
+        }
+    }
 }

src/Phan/CLI.php

@@ -1053,11 +1053,16 @@ private function maybeReadConfigFile(bool $require_config_exists)
             ]);
 
         // Totally cool if the file isn't there
-        if (!file_exists($config_file_name)) {
+        if ($config_file_name === false || !file_exists($config_file_name)) {
             if ($require_config_exists) {
                 // But if the CLI option --require-config-exists is provided, exit immediately.
                 // (Include extended help documenting that option)
-                $this->usage("Could not find a config file at '$config_file_name', but --require-config-exists was set", EXIT_FAILURE, true);
+                if ($config_file_name !== false) {
+                    $this->usage("Could not find a config file at '$config_file_name', but --require-config-exists was set", EXIT_FAILURE, true);
+                } else {
+                    $this->usage(sprintf("Could not figure out the path for config file '%s', but --require-config-exists was set", $this->config_file), EXIT_FAILURE, true);
+                }
+
             }
             return;
         }

src/Phan/Issue.php

@@ -311,6 +311,7 @@ class Issue
     const CompatibleUseIterablePHP71         = 'PhanCompatibleUseIterablePHP71';
     const CompatibleUseObjectPHP71           = 'PhanCompatibleUseObjectPHP71';
     const CompatibleMultiExceptionCatchPHP70 = 'PhanCompatibleMultiExceptionCatchPHP70';
+    const CompatibleNegativeStringOffset     = 'PhanCompatibleNegativeStringOffset';
 
     // Issue::CATEGORY_GENERIC
     const TemplateTypeConstant       = 'PhanTemplateTypeConstant';
@@ -2614,6 +2615,14 @@ public static function issueMap()
                 self::REMEDIATION_B,
                 3011
             ),
+            new Issue(
+                self::CompatibleNegativeStringOffset,
+                self::CATEGORY_COMPATIBLE,
+                self::SEVERITY_CRITICAL,
+                "Using negative string offset is not available before PHP 7.1 (emits an 'Uninitialized string offset' notice)",
+                self::REMEDIATION_B,
+                3012
+            ),
 
             // Issue::CATEGORY_GENERIC
             new Issue(

src/Phan/Parse/ParseVisitor.php

@@ -1258,4 +1258,5 @@ public function visitBinaryOp(Node $node)
     {
         return $this->context;
     }
+
 }

tests/php70_test/expected/009_negative_string_offset.php.expected

@@ -0,0 +1,2 @@
+src/009_negative_string_offset.php:5 PhanCompatibleNegativeStringOffset Using negative string offset is not available before PHP 7.1 (emits an 'Uninitialized string offset' notice)
+src/009_negative_string_offset.php:6 PhanCompatibleNegativeStringOffset Using negative string offset is not available before PHP 7.1 (emits an 'Uninitialized string offset' notice)

tests/php70_test/src/009_negative_string_offset.php

@@ -0,0 +1,9 @@
+<?php
+
+$string = "Phan is awesome";
+
+$char1 = $string{-1};
+$char2 = $string[-2];
+
+// accessing negative array index should not emit the warning
+$array_element = [ -1 => 1 ][-1];

tests/php70_test/test.sh

@@ -12,7 +12,10 @@ if [[ $? != 0 ]]; then
 	exit 1
 fi
 echo "Running phan in '$PWD' ..."
-rm $ACTUAL_PATH -f || exit 1
+
+if [ -f $ACTUAL_PATH ]; then
+    rm -f $ACTUAL_PATH || exit 1
+fi
 
 # We use the polyfill parser because it behaves consistently in all php versions.
 ../../phan --force-polyfill-parser --memory-limit 1G | tee $ACTUAL_PATH