[clang] [clang][deps] Fix dependency scanner misidentifying 'import::' as module partition (PR #148674)

[Naveen Seth Hanig via cfe-commits]

https://github.com/naveen-seth created https://github.com/llvm/llvm-project/pull/148674

The dependency directive scanner was incorrectly classifying namespaces such as `import::inner xi` as directives. According to [P1857R3](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1857r3.html#tony-table), `import` should not be treated as a directive when followed by `::`.
This change fixes that behavior.

>From bb1c20a40fa8635b8987733708979729d54aa02e Mon Sep 17 00:00:00 2001
From: Naveen Seth Hanig <naveen.hanig at outlook.com>
Date: Mon, 14 Jul 2025 18:44:01 +0200
Subject: [PATCH] [clang][deps] Fix dependency scanner misidentifying
 'import::' as module partition

The dependency directive scanner was incorrectly classifying
namespaces such as `import::inner xi` as directives.
According to P1857R3, `import` should not be treated as a directive
when followed by `::`.
This change fixes that behavior.
---
 clang/lib/Lex/DependencyDirectivesScanner.cpp        |  7 +++++++
 .../Lex/DependencyDirectivesScannerTest.cpp          | 12 ++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/clang/lib/Lex/DependencyDirectivesScanner.cpp b/clang/lib/Lex/DependencyDirectivesScanner.cpp
index d894c265a07a2..869c9cea566b6 100644
--- a/clang/lib/Lex/DependencyDirectivesScanner.cpp
+++ b/clang/lib/Lex/DependencyDirectivesScanner.cpp
@@ -722,6 +722,13 @@ bool Scanner::lexModule(const char *&First, const char *const End) {
       skipLine(First, End);
       return false;
     }
+    // A module partition starts with exactly one ':'. If we have '::', this is
+    // a scope resolution instead and shouldn't be recognized as a directive
+    // per P1857R3.
+    if (First + 1 != End && First[1] == ':') {
+      skipLine(First, End);
+      return false;
+    }
     // `import:(type)name` is a valid ObjC method decl, so check one more token.
     (void)lexToken(First, End);
     if (!tryLexIdentifierOrSkipLine(First, End))
diff --git a/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp b/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
index d2ef27155df94..4d532826cbd60 100644
--- a/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
+++ b/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
@@ -1151,6 +1151,18 @@ TEST(MinimizeSourceToDependencyDirectivesTest, ObjCMethodArgs) {
   EXPECT_STREQ("<TokBeforeEOF>\n", Out.data());
 }
 
+TEST(MinimizeSourceToDependencyDirectivesTest, CxxModulesImportScopeResolution) {
+  SmallString<16> Out;
+  SmallVector<dependency_directives_scan::Token, 2> Tokens;
+  SmallVector<Directive, 1> Directives;
+
+  StringRef Source = "import::inner xi = {};'\n"
+                     "module::inner yi = {};";
+  ASSERT_FALSE(
+      minimizeSourceToDependencyDirectives(Source, Out, Tokens, Directives));
+  EXPECT_STREQ("<TokBeforeEOF>\n", Out.data());
+}
+
 TEST(MinimizeSourceToDependencyDirectivesTest, TokensBeforeEOF) {
   SmallString<128> Out;