[lld-link] For suppressible warnings, print the suppressing flag.

[hans]

COFF/Driver.cpp

809

Would it be helpful to make warn() take an optional warning number and tweak the message accordingly?

"no /ignore:1234" is a bit terse for my taste. How about "suppress with /ignore:1234" or "pass /ignore:1234 to suppress" or something similar?

[thakis]

COFF/Driver.cpp

809

That's too word for me. I had "[/ignore:1245 to ignore]" but didn't like the redundant "ignore". I like the terse message, it's similar to how clang prints warning flags.

Making warn() responsible for this makes sense once we have more than 2 uses. For now, this seems ok to me.

[ruiu]

COFF/Driver.cpp

809

"[no /ignore:4217]" is repeated a few times in this patch indeed, but I don't think that is too many to add a new parameter to warn(). I'm fine with what you did in this patch.

[thakis]

COFF/Driver.cpp

809

Another idea would be to print [LNK4217] which is even terser and which finds the link.exe docs in search engines, but it's surprisingly difficult to find the /ignore: flag that way. (OTOH, with the /ignore:4217 it's hard to realize that the thing to search the web for is "lnk4217"). I don't have a strong preference between [no /ignore:4217] and [LNK4217], I probably weakly prefer the latter a bit. Hans, since you had an opinion on the spelling, wdyt?

[hans]

COFF/Driver.cpp

809

It's hard to come up with anything terse that's also really clear.

[LNK1234] is really short, and also very compatible so maybe that's the way to go.

[thakis]

r327257, thanks!

Maybe we should also print something like

                                                                             
"use /ignore: to suppress numbered warnings"

if we print at least one warning with a number. Not in this change here, though.

COFF/Driver.cpp

static void parseOrderFile(StringRef Arg) {
   // considered to have the lowest priority 0 and are placed at
   // end of an output section.
   for (std::string S : args::getLines(MB->getMemBufferRef())) {
     if (Config->Machine == I386 && !isDecorated(S))
       S = "_" + S;
 
     if (Set.count(S) == 0) {
       if (Config->WarnMissingOrderSymbol)
-        warn("/order:" + Arg + ": missing symbol: " + S);
+        warn("/order:" + Arg + ": missing symbol: " + S + " [no /ignore:4037]");
     }
     else
       Config->Order[S] = INT_MIN + Config->Order.size();
   }
 }
 
 void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   // If the first command line argument is "/lib", link.exe acts like lib.exe.

COFF/SymbolTable.cpp

if (Undefs.empty() && LocalImports.empty())
     return;
 
   for (Symbol *B : Config->GCRoot) {
     if (Undefs.count(B))
       errorOrWarn("<root>: undefined symbol: " + B->getName());
     if (Config->WarnLocallyDefinedImported)
       if (Symbol *Imp = LocalImports.lookup(B))
         warn("<root>: locally defined symbol imported: " + Imp->getName() +
-             " (defined in " + toString(Imp->getFile()) + ")");
+             " (defined in " + toString(Imp->getFile()) +
+             ") [no /ignore:4217]");
   }
 
   for (ObjFile *File : ObjFile::Instances) {
     for (Symbol *Sym : File->getSymbols()) {
       if (!Sym)
         continue;
       if (Undefs.count(Sym))
         errorOrWarn(toString(File) + ": undefined symbol: " + Sym->getName());
       if (Config->WarnLocallyDefinedImported)
         if (Symbol *Imp = LocalImports.lookup(Sym))
           warn(toString(File) + ": locally defined symbol imported: " +
                Imp->getName() + " (defined in " + toString(Imp->getFile()) +
-               ")");
+               ") [no /ignore:4217]");
     }
   }
 }
 
 std::pair<Symbol *, bool> SymbolTable::insert(StringRef Name) {
   Symbol *&Sym = SymMap[CachedHashStringRef(Name)];
   if (Sym)
     return {Sym, false};