make skipping of checks after invalid includes configurable

as suggested in the PR it's best to make the setting configurable.

In order not to break existing installations, we default to keeping the
old behaviour, but in a later version of psalm, we might change the
default.

config.xsd

@@ -68,6 +68,7 @@
         <xs:attribute name="useDocblockPropertyTypes" type="xs:boolean" default="false" />
         <xs:attribute name="usePhpDocMethodsWithoutMagicCall" type="xs:boolean" default="false" />
         <xs:attribute name="usePhpDocPropertiesWithoutMagicCall" type="xs:boolean" default="false" />
+        <xs:attribute name="skipChecksOnUnresolvableIncludes" type="xs:boolean" default="true" />
     </xs:complexType>
 
     <xs:complexType name="ProjectFilesType">

docs/running_psalm/configuration.md

@@ -275,6 +275,17 @@ Set the php version psalm should assume when checking and/or fixing the project.
 
 This can be overridden on the command-line using the `--php-version=` flag which takes the highest precedence over both the `phpVersion` setting and the version derived from `composer.json`.
 
+#### skipChecksOnUnresolvableIncludes
+```xml
+<psalm
+  skipChecksOnUnresolvableIncludes="[bool]"
+>
+```
+
+When `true`, Psalm will skip checking classes, variables and functions after it comes across an `include` or `require` it cannot resolve. This allows code to reference functions and classes unknown to Psalm.
+
+For backwards compatibility, this defaults to `true`, but if you do not rely on dynamically generated includes to cause classes otherwise unknown to psalm to come into existence, it's recommended you set this to `false` in order to reliably detect errors that would be fatal to PHP at runtime.
+
 ### Running Psalm
 
 #### autoloader

src/Psalm/Config.php

@@ -291,6 +291,11 @@ class Config
      */
     public $use_phpdoc_property_without_magic_or_parent = false;
 
+    /**
+     * @var bool
+     */
+    public $skip_checks_on_unresolvable_includes = true;
+
     /**
      * @var bool
      */
@@ -765,6 +770,7 @@ class Config
             'ensureArrayStringOffsetsExist' => 'ensure_array_string_offsets_exist',
             'ensureArrayIntOffsetsExist' => 'ensure_array_int_offsets_exist',
             'reportMixedIssues' => 'show_mixed_issues',
+            'skipChecksOnUnresolvableIncludes' => 'skip_checks_on_unresolvable_includes'
         ];
 
         foreach ($booleanAttributes as $xmlName => $internalName) {

src/Psalm/Internal/Analyzer/Statements/Expression/IncludeAnalyzer.php

@@ -160,6 +160,11 @@ class IncludeAnalyzer
                         $global_context
                     );
                 } catch (\Psalm\Exception\UnpreparedAnalysisException $e) {
+                    if ($config->skip_checks_on_unresolvable_includes) {
+                        $context->check_classes = false;
+                        $context->check_variables = false;
+                        $context->check_functions = false;
+                    }
                 }
 
                 foreach ($include_file_analyzer->getRequiredFilePaths() as $required_file_path) {
@@ -200,6 +205,12 @@ class IncludeAnalyzer
             }
         }
 
+        if ($config->skip_checks_on_unresolvable_includes) {
+            $context->check_classes = false;
+            $context->check_variables = false;
+            $context->check_functions = false;
+        }
+
         return null;
     }
 

tests/IncludeTest.php

@@ -37,6 +37,7 @@ class IncludeTest extends TestCase
         }
 
         $config = $codebase->config;
+        $config->skip_checks_on_unresolvable_includes = true;
 
         foreach ($error_levels as $error_level) {
             $config->setCustomErrorLevel($error_level, \Psalm\Config::REPORT_SUPPRESS);
@@ -83,6 +84,7 @@ class IncludeTest extends TestCase
         }
 
         $config = $codebase->config;
+        $config->skip_checks_on_unresolvable_includes = false;
 
         $this->expectException(\Psalm\Exception\CodeException::class);
         $this->expectExceptionMessageRegExp('/\b' . preg_quote($error_message, '/') . '\b/');
@@ -569,6 +571,25 @@ class IncludeTest extends TestCase
                     getcwd() . DIRECTORY_SEPARATOR . 'a' . DIRECTORY_SEPARATOR . 'b' . DIRECTORY_SEPARATOR . 'c' . DIRECTORY_SEPARATOR . 'd' . DIRECTORY_SEPARATOR . 'script.php',
                 ],
             ],
+            'undefinedMethodAfterInvalidRequire' => [
+                'files' => [
+                    getcwd() . DIRECTORY_SEPARATOR . 'file2.php' => '<?php
+                        /** @psalm-suppress MissingFile */
+                        require("doesnotexist.php");
+                        require("file1.php");
+
+                        foo();
+                        bar();
+                        ',
+                    getcwd() . DIRECTORY_SEPARATOR . 'file1.php' => '<?php
+                        function bar(): void {}
+                        ',
+                ],
+                'files_to_check' => [
+                    getcwd() . DIRECTORY_SEPARATOR . 'file2.php',
+                ],
+            ],
+
         ];
     }