[flang][Semantics] Ensure deterministic mod file output (#128655)

This PR adds a test to ensure deterministic ordering in `.mod` files. It
also includes related changes to prevent non-deterministic symbol
ordering caused by pointers outside the cooked source. This issue is
particularly noticeable when using Flang as a library and compiling the
same files multiple times.

1 files changed, 2 insertions, 19 deletions

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index bef934b..82c43d9 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -836,18 +836,6 @@ void ModFileWriter::PutUseExtraAttr(
   }
 }
 
-static inline SourceName NameInModuleFile(const Symbol &symbol) {
-  if (const auto *use{symbol.detailsIf<UseDetails>()}) {
-    if (use->symbol().attrs().test(Attr::PRIVATE)) {
-      // Avoid the use in sorting of names created to access private
-      // specific procedures as a result of generic resolution;
-      // they're not in the cooked source.
-      return use->symbol().name();
-    }
-  }
-  return symbol.name();
-}
-
 // Collect the symbols of this scope sorted by their original order, not name.
 // Generics and namelists are exceptions: they are sorted after other symbols.
 void CollectSymbols(const Scope &scope, SymbolVector &sorted,
@@ -882,13 +870,8 @@ void CollectSymbols(const Scope &scope, SymbolVector &sorted,
       sorted.push_back(symbol);
     }
   }
-  // Sort most symbols by name: use of Symbol::ReplaceName ensures the source
-  // location of a symbol's name is the first "real" use.
-  auto sorter{[](SymbolRef x, SymbolRef y) {
-    return NameInModuleFile(*x).begin() < NameInModuleFile(*y).begin();
-  }};
-  std::sort(sorted.begin(), sorted.end(), sorter);
-  std::sort(generics.begin(), generics.end(), sorter);
+  std::sort(sorted.begin(), sorted.end(), SymbolSourcePositionCompare{});
+  std::sort(generics.begin(), generics.end(), SymbolSourcePositionCompare{});
   sorted.insert(sorted.end(), generics.begin(), generics.end());
   sorted.insert(sorted.end(), namelist.begin(), namelist.end());
   for (const auto &pair : scope.commonBlocks()) {