[cfe-dev] Tooling vs -fdelayed-template-parsing WAS: Clang-cl.exe and the VC++ preprocessor

[Kim Gräsman]

Hi Manuel,

On Mon, Aug 4, 2014 at 2:43 PM, Manuel Klimek <klimek at google.com> wrote:

>
> Can we somehow get this into the tooling infrastructure? I'd consider it a
> bug if fdelayed-template-parsing leads to ASTs that don't have the
> templates; from reading the docs, it seems like all it should do is parse
> them at the end of the translation unit, or am I missing something?
>

This is what we did in IWYU, right after our original AST traversal:

+  void InstantiateLateParsedFunctions() {
+    const vector<FunctionDecl*>& late_parsed_decls =
LateParsedFunctionDecls();
+    clang::Sema& sema = compiler()->getSema();
+
+    // If we have any late-parsed functions, make sure the
+    // -fdelayed-template-parsing flag is on. Otherwise we don't know where
+    // they came from.
+    CHECK_((compiler()->getLangOpts().DelayedTemplateParsing ||
+            late_parsed_decls.empty()) &&
+           "Should not have late-parsed decls without "
+           "-fdelayed-template-parsing.");
+
+    for (Each<FunctionDecl*> it(&late_parsed_decls); !it.AtEnd(); ++it) {
+      FunctionDecl* decl = *it;
+      if (decl->isLateTemplateParsed()) {
+        // Force parsing and AST building of the yet-uninstantiated
function
+        // template body.
+        clang::LateParsedTemplate* lpt = sema.LateParsedTemplateMap[decl];
+        sema.LateTemplateParser(sema.OpaqueParser, *lpt);
+
+        // Traverse the AST fragment again to run IWYU analysis on the new
+        // nodes.
+        TraverseDecl(decl);
+      }
+    }
+  }

After parsing, you'd have to run a second pass of your matcher AST visitor.
I could get away with just visiting the instantiated Decl (or so I hope),
but that might not be enough for your needs.

I'm still not sure this is 100% right, of course.

- Kim
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