[clang] [clang][modules] Add warning for symlinks to modular headers (PR #188059)

[Jan Svoboda via cfe-commits]

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@@ -1896,6 +1916,77 @@ static bool suggestModule(HeaderSearch &HS, ModuleMap::KnownHeader Module,
   return true;
 }
 
+void HeaderSearch::diagnoseUncoveredSymlink(FileEntryRef File,
+                                            ModuleMap::KnownHeader &Module,
+                                            const DirectoryEntry *Root) {
+  if (!Module)
+    return;
+
+  if (!HSOpts.ImplicitModuleMaps || Module.getModule()->isPartOfFramework() ||
+      !Module.getModule()->isModuleMapModule())
+    return;
+
+  if (Diags.isIgnored(diag::warn_mmap_deprecated_symlink_to_modular_header,
+                      Module.getModule()->DefinitionLoc))
+    return;
+
+  if (File.isDeviceFile() || File.isNamedPipe())
+    return;
+
+  llvm::SmallString<128> AbsPath(File.getName());
+  FileMgr.makeAbsolutePath(AbsPath);
+  llvm::sys::path::remove_dots(AbsPath, /*remove_dot_dot=*/true);
+
+  // NOTE: This path may be redirected, LLVM's VFS does not model symlinks, so
+  //       it's possible this fails. The diagnostic is worded as such.
+  llvm::SmallString<128> LinkTarget;
+  if (llvm::sys::fs::readlink(AbsPath, LinkTarget))
+    return;
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jansvoboda11 wrote:

We chatted offline and I think this is fine for the time being as a best-effort approach.

https://github.com/llvm/llvm-project/pull/188059