[clang-tools-extra] [clangd] Document the cases in which Dex::Files and IdxContents are populated (PR #118906)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-tools-extra

Author: Nathan Ridge (HighCommander4)

<details>
<summary>Changes</summary>

This is a follow-up to https://github.com/llvm/llvm-project/pull/118324 to document that the `Dex` fields `Files` and `IdxContents` are intentionally only used in some cases, and describe what those cases are.

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Full diff: https://github.com/llvm/llvm-project/pull/118906.diff


1 Files Affected:

- (modified) clang-tools-extra/clangd/index/dex/Dex.h (+2) 


``````````diff
diff --git a/clang-tools-extra/clangd/index/dex/Dex.h b/clang-tools-extra/clangd/index/dex/Dex.h
index 69e161d51135b6..8ae4050d004e28 100644
--- a/clang-tools-extra/clangd/index/dex/Dex.h
+++ b/clang-tools-extra/clangd/index/dex/Dex.h
@@ -121,6 +121,8 @@ class Dex : public SymbolIndex {
   llvm::DenseMap<std::pair<SymbolID, uint8_t>, std::vector<SymbolID>> Relations;
   std::shared_ptr<void> KeepAlive; // poor man's move-only std::any
   // Set of files which were used during this index build.
+  // Files and IdxContents are only populated for dynamic and background
+  // indexes, not static indexes.
   llvm::StringSet<> Files;
   // Contents of the index (symbols, references, etc.)
   IndexContents IdxContents;

``````````

</details>


https://github.com/llvm/llvm-project/pull/118906