[symbolizer][NFC] Reorganize parsing input binary file

[sepavloff]

Summary

Now llvm-symbolizer prints input string if parsing command failed,
whithout explanation that is wrong. As a first step in making the
interface more user-friendly, this change reorganize parsing so that
generation of messages becomes easier.

[ikudrin]

LGTM

llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp

205–212

Use else if here to reduce the nesting.

209–213

The new code has a different result than the old one if, for example, InputString consists of only one word, i.e. ModuleName was set to this word, while with the changed code it remains empty.

[jhenderson]

LGTM, with nits.

llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp

175

Here and below "is already seen" -> "has already been seen"

181

I'd probably add a blank line before this if.

183

"is already" -> "has already been"
"in command line" -> "on the command-line"

207

211

[sepavloff]

Thanks!

llvm/tools/llvm-symbolizer/llvm-symbolizer.cpp

static StringRef getSpaceDelimitedWord(StringRef &Source) {
   Source = StringRef(Pos, Source.end() - Pos);
   return Result;
 }
 
 static bool parseCommand(StringRef BinaryName, bool IsAddr2Line,
                          StringRef InputString, Command &Cmd,
                          std::string &ModuleName, object::BuildID &BuildID,
                          uint64_t &ModuleOffset) {
-  ModuleName = "";
+  ModuleName = BinaryName;
   if (InputString.consume_front("CODE ")) {
     Cmd = Command::Code;
   } else if (InputString.consume_front("DATA ")) {
     Cmd = Command::Data;
   } else if (InputString.consume_front("FRAME ")) {
     Cmd = Command::Frame;
   } else {
     // If no cmd, assume it's CODE.
     Cmd = Command::Code;
   }
 
-  // Skip delimiters and parse input filename (if needed).
-  if (BinaryName.empty() && BuildID.empty()) {
-    bool HasFilePrefix = false;
-    bool HasBuildIDPrefix = false;
-    while (true) {
-      if (InputString.consume_front("FILE:")) {
-        if (HasFilePrefix)
-          return false;
-        HasFilePrefix = true;
-        continue;
-      }
-      if (InputString.consume_front("BUILDID:")) {
-        if (HasBuildIDPrefix)
-          return false;
-        HasBuildIDPrefix = true;
-        continue;
-      }
-      break;
-    }
-    if (HasFilePrefix && HasBuildIDPrefix)
-      return false;
+  // Parse optional input file specification.
+  while (!InputString.empty()) {
+    InputString = InputString.ltrim();
+      if (HasFilePrefix || HasBuildIDPrefix)
+        // Input file specification prefix has already been seen.
+      if (HasBuildIDPrefix || HasFilePrefix)
+        // Input file specification prefix has already been seen.
 
-    ModuleName = getSpaceDelimitedWord(InputString);
-    if (ModuleName.empty())
+  if (HasBuildIDPrefix || HasFilePrefix) {
+    if (!BinaryName.empty() || !BuildID.empty())
+      // Input file has already been specified on the command line.
+      return false;
+    StringRef Name = getSpaceDelimitedWord(InputString);
+    if (Name.empty())
+      // Wrong name for module file.
       return false;
     if (HasBuildIDPrefix) {
-      BuildID = parseBuildID(ModuleName);
+      BuildID = parseBuildID(Name);
       if (BuildID.empty())
+        // Wrong format of BuildID hash.
         return false;
-      ModuleName.clear();
-    }
     } else {
-    ModuleName = BinaryName.str();
+      ModuleName = Name;
+    }
+  } else if (BinaryName.empty() && BuildID.empty()) {
+    // No input file has been specified. If the input string contains at least
+    // two items, assume that the first item is a file name.
+    ModuleName = getSpaceDelimitedWord(InputString);
+    if (ModuleName.empty() || InputString.empty())
+      // No input filename has been specified.
+      return false;
   }
 
   // Skip delimiters and parse module offset.
   InputString = InputString.ltrim();
   int OffsetLength = InputString.find_first_of(" \n\r");
   StringRef Offset = InputString.substr(0, OffsetLength);
   // GNU addr2line assumes the offset is hexadecimal and allows a redundant
   // "0x" or "0X" prefix; do the same for compatibility.
   if (IsAddr2Line)