[Driver] Parse Debian version as integer when possible. NFC

[mgorny]

Summary

Replace the string matching for /etc/debian_version with split
integer/string matching algorithm. When the file contains 'major.minor'
version number, parse the major version as integer and use a switch
clause to match it. Otherwise, attempt 'codename/sid' matching using
a StringSwitch.

[bruno]

lib/Driver/ToolChains.cpp

3903 ↗

(On Diff #74897)

clang-format the switch: case's should be aligned with it.

3917 ↗

(On Diff #74897)

You can remove the else and just return llvm::StringSwitch...

[mgorny]

Restructured and reformatted as requested.

[bruno]

LGTM!

[mgorny]

Thanks for the review. I'll now look into updating the code for other distros to follow suit.

cfe/trunk/lib/Driver/ToolChains.cpp

if (Data.startswith("Red Hat Enterprise Linux") ||
         return RHEL5;
     }
     return UnknownDistro;
   }
 
   File = D.getVFS().getBufferForFile("/etc/debian_version");
   if (File) {
     StringRef Data = File.get()->getBuffer();
-    if (Data[0] == '5')
+    // Contents: < major.minor > or < codename/sid >
+    int MajorVersion;
+    if (!Data.split('.').first.getAsInteger(10, MajorVersion)) {
+      switch (MajorVersion) {
+      case 5:
         return DebianLenny;
-    else if (Data.startswith("squeeze/sid") || Data[0] == '6')
+      case 6:
         return DebianSqueeze;
-    else if (Data.startswith("wheezy/sid") || Data[0] == '7')
+      case 7:
         return DebianWheezy;
-    else if (Data.startswith("jessie/sid") || Data[0] == '8')
+      case 8:
         return DebianJessie;
-    else if (Data.startswith("stretch/sid") || Data[0] == '9')
+      case 9:
         return DebianStretch;
+      default:
         return UnknownDistro;
       }
+    }
+    return llvm::StringSwitch<Distro>(Data.split("\n").first)
+        .Case("squeeze/sid", DebianSqueeze)
+        .Case("wheezy/sid", DebianWheezy)
+        .Case("jessie/sid", DebianJessie)
+        .Case("stretch/sid", DebianStretch)
+        .Default(UnknownDistro);
+  }
 
   if (D.getVFS().exists("/etc/SuSE-release"))
     return OpenSUSE;
 
   if (D.getVFS().exists("/etc/exherbo-release"))
     return Exherbo;
 
   if (D.getVFS().exists("/etc/arch-release"))