GRAM: allow unsafe modifier for module and module declaration items

Note, `unsafe` is semantically invalid in case of module/module declaration items. The corresponding change is made to improve error message.
See the corresponding change in rustc: rust-lang/rust#75857

Author: Undin

src/main/grammars/RustParser.bnf

@@ -681,8 +681,8 @@ upper ExternCrateItem ::= extern crate (identifier | self) Alias? ';' {
   elementTypeFactory = "org.rust.lang.core.stubs.StubImplementationsKt.factory"
 }
 
-upper ModItem ::= mod identifier '{' InnerAttr* Items '}' {
-  pin = 3
+upper ModItem ::= unsafe? mod identifier '{' InnerAttr* Items '}' {
+  pin = 4
   name = ""
   implements = [ "org.rust.lang.core.psi.ext.RsNameIdentifierOwner"
                  "org.rust.lang.core.psi.ext.RsItemElement"
@@ -693,7 +693,7 @@ upper ModItem ::= mod identifier '{' InnerAttr* Items '}' {
   elementTypeFactory = "org.rust.lang.core.stubs.StubImplementationsKt.factory"
 }
 
-upper ModDeclItem ::= mod identifier ';' {
+upper ModDeclItem ::= unsafe? mod identifier ';' {
   pin = 'identifier' // make sure `ModDeclItem` goes **after** `ModItem`
   name = ""
   implements = [ "org.rust.lang.core.psi.ext.RsMandatoryReferenceElement"

src/main/kotlin/org/rust/lang/core/parser/RustParserDefinition.kt

@@ -104,6 +104,6 @@ class RustParserDefinition : ParserDefinition {
         /**
          * Should be increased after any change of parser rules
          */
-        const val PARSER_VERSION: Int = LEXER_VERSION + 28
+        const val PARSER_VERSION: Int = LEXER_VERSION + 29
     }
 }

src/test/resources/org/rust/lang/core/parser/fixtures/complete/mod.rs

@@ -19,7 +19,11 @@ mod empty {
 
 pub mod pub_mod {}
 pub(crate) mod pub_crate_mod {}
+unsafe mod unsafe_crate_mod {} // semantically invalid
+pub unsafe mod pub_unsafe_crate_mod {} // semantically invalid
 
 mod mod_decl;
 pub mod pub_mod_decl;
 pub(crate) mod pub_crate_mod_decl;
+unsafe mod unsafe_mod_decl; // semantically invalid
+pub unsafe mod pub_unsafe_mod_decl; // semantically invalid

src/test/resources/org/rust/lang/core/parser/fixtures/complete/mod.txt

@@ -160,6 +160,33 @@ FILE
     PsiWhiteSpace(' ')
     PsiElement({)('{')
     PsiElement(})('}')
+  PsiWhiteSpace('\n')
+  RsModItemImpl(MOD_ITEM)
+    PsiElement(unsafe)('unsafe')
+    PsiWhiteSpace(' ')
+    PsiElement(mod)('mod')
+    PsiWhiteSpace(' ')
+    PsiElement(identifier)('unsafe_crate_mod')
+    PsiWhiteSpace(' ')
+    PsiElement({)('{')
+    PsiElement(})('}')
+  PsiWhiteSpace(' ')
+  RsModItemImpl(MOD_ITEM)
+    PsiComment(<EOL_COMMENT>)('// semantically invalid')
+    PsiWhiteSpace('\n')
+    RsVisImpl(VIS)
+      PsiElement(pub)('pub')
+    PsiWhiteSpace(' ')
+    PsiElement(unsafe)('unsafe')
+    PsiWhiteSpace(' ')
+    PsiElement(mod)('mod')
+    PsiWhiteSpace(' ')
+    PsiElement(identifier)('pub_unsafe_crate_mod')
+    PsiWhiteSpace(' ')
+    PsiElement({)('{')
+    PsiElement(})('}')
+  PsiWhiteSpace(' ')
+  PsiComment(<EOL_COMMENT>)('// semantically invalid')
   PsiWhiteSpace('\n\n')
   RsModDeclItemImpl(MOD_DECL_ITEM)
     PsiElement(mod)('mod')
@@ -189,3 +216,26 @@ FILE
     PsiWhiteSpace(' ')
     PsiElement(identifier)('pub_crate_mod_decl')
     PsiElement(;)(';')
+  PsiWhiteSpace('\n')
+  RsModDeclItemImpl(MOD_DECL_ITEM)
+    PsiElement(unsafe)('unsafe')
+    PsiWhiteSpace(' ')
+    PsiElement(mod)('mod')
+    PsiWhiteSpace(' ')
+    PsiElement(identifier)('unsafe_mod_decl')
+    PsiElement(;)(';')
+  PsiWhiteSpace(' ')
+  RsModDeclItemImpl(MOD_DECL_ITEM)
+    PsiComment(<EOL_COMMENT>)('// semantically invalid')
+    PsiWhiteSpace('\n')
+    RsVisImpl(VIS)
+      PsiElement(pub)('pub')
+    PsiWhiteSpace(' ')
+    PsiElement(unsafe)('unsafe')
+    PsiWhiteSpace(' ')
+    PsiElement(mod)('mod')
+    PsiWhiteSpace(' ')
+    PsiElement(identifier)('pub_unsafe_mod_decl')
+    PsiElement(;)(';')
+  PsiWhiteSpace(' ')
+  PsiComment(<EOL_COMMENT>)('// semantically invalid')

src/test/resources/org/rust/lang/core/parser/fixtures/partial/fn.txt

@@ -105,7 +105,7 @@ FILE
     PsiElement(})('}')
   PsiWhiteSpace('\n\n')
   PsiElement(unsafe)('unsafe')
-  PsiErrorElement:extern, fn, impl or trait expected, got 'const'
+  PsiErrorElement:extern, fn, impl, mod or trait expected, got 'const'
     <empty list>
   PsiWhiteSpace(' ')
   RsFunctionImpl(FUNCTION)