[llvm-ar] Prevent automatic conversion from thin to full archive

[gbreynoo]

Summary

llvm-ar silently converts a thin archive to a regular archive when you specify a modification operation (e.g. 'r') without the 'T' modifier. This is probably not what is normally intended, since it would be very easy to forget the modifier. If a user is trying to convert between thin and full archives then they can explicitly use the 'L' command to create a new archive.

[gbreynoo]

I believe Gnu-ar commands without T on thin archives do not auto convert to "full" archives:

• Move and Delete work as intended
• Replace and Quick Append errors

I think a consistent approach would be best, so I'm happy to just go with an error if that is preferred.

[MaskRay]

May be worth stating that GNU ar rejects 'r' and 'q' for a thin archive if 'T'/--thin is not specified.

% ar r a.a b.o
ar: Cannot convert existing thin library a.a to normal format

I do not have a strong opinion whether llvm-ar 'r' and 'q' should report a similar error.
Supporting the operation in the absence of explicit 'T'/--thin seems useful.

llvm/test/tools/llvm-ar/full-to-thin-archive.test

12

Prefer two-dash long options for FileCheck. And you already used the form for --check-prefixes:)

llvm/test/tools/llvm-ar/thin-to-full-archive.test

7

ditto

27

If a positive pattern can serve the same purpose as a negative pattern. I'd use the positive one since a negative one may go stale without being noticed.

llvm/tools/llvm-ar/llvm-ar.cpp

658

[MaskRay]

llvm/test/tools/llvm-ar/full-to-thin-archive.test

10

llvm/test/tools/llvm-ar/full-to-thin-archive.test

 ## Test archives do not convert to thin archives.
 
 # RUN: rm -rf %t && mkdir -p %t
 # RUN: llvm-ar qc %t/archive.a %s
 # RUN: not llvm-ar qT %t/archive.a %s 2>&1 | FileCheck %s
 # RUN: not llvm-ar rT %t/archive.a %s 2>&1 | FileCheck %s
 
 # CHECK: error: cannot convert a regular archive to a thin one
+
+## Test that you can add a full archive's contents to a thin archive with 'L'
+# RUN: llvm-ar -TqcL %t/thin.a %t/archive.a
+# RUN: FileCheck --check-prefixes=THIN --input-file=%t/thin.a %s
+
+THIN: !<thin>

llvm/test/tools/llvm-ar/thin-to-full-archive.test

+## Test thin archives do not siletly convert to full archives on write.
+
+# RUN: rm -f %tthin.a %tfull.a 
+
+# RUN: llvm-ar -Trc %tthin.a %S/Inputs/a.txt
+# RUN: FileCheck --check-prefixes=THIN --input-file=%tthin.a %s
+
+# RUN: llvm-ar -q %tthin.a %S/Inputs/b.txt
+# RUN: FileCheck --check-prefixes=THIN --input-file=%tthin.a %s
+
+# RUN: llvm-ar -r %tthin.a %S/Inputs/c.txt
+# RUN: FileCheck --check-prefixes=THIN --input-file=%tthin.a %s
+
+# RUN: llvm-ar -am %S/Inputs/a.txt %tthin.a %S/Inputs/c.txt
+# RUN: FileCheck --check-prefixes=THIN --input-file=%tthin.a %s
+
+# RUN: llvm-ar -d %tthin.a %S/Inputs/c.txt
+# RUN: FileCheck --check-prefixes=THIN --input-file=%tthin.a %s
+
+THIN: !<thin>
+
+## Test that you can add a thin archive's contents to a full archive with 'L'
+# RUN: llvm-ar -qcL %tfull.a %tthin.a
+# RUN: FileCheck --check-prefixes=FULL --input-file=%tfull.a %s
+
+FULL: !<arch>

llvm/tools/llvm-ar/llvm-ar.cpp

static void performReadOperation(ArchiveOperation Operation,
   exit(1);
 }
 
 static void addChildMember(std::vector<NewArchiveMember> &Members,
                            const object::Archive::Child &M,
                            bool FlattenArchive = false) {
   if (Thin && !M.getParent()->isThin())
     fail("cannot convert a regular archive to a thin one");
+
+  // Avoid converting an existing thin archive to a regular one.
+  if (!AddLibrary && M.getParent()->isThin())
+    Thin = true;
+
   Expected<NewArchiveMember> NMOrErr =
       NewArchiveMember::getOldMember(M, Deterministic);
   failIfError(NMOrErr.takeError());
   // If the child member we're trying to add is thin, use the path relative to
   // the archive it's in, so the file resolves correctly.
   if (Thin && FlattenArchive) {
     StringSaver Saver(Alloc);
     Expected<std::string> FileNameOrErr(M.getName());