[ELF] Add "warning", "error" and "fatal error" prefixes to linker messages

[evgeny777]

Summary

The primary goal is integration with MS visual studio. Also this makes possible distinguishing warnings from errors when lld is invoked from command line.

[ruiu]

Do we have to distinguish "fatal error" from "error"? I think it can just be "error" and "warning".

[evgeny777]

AFAIK gold reports both "fatal error" and error as well. Also "fatal error" is different from "error" in lld, because it causes immediate exit.
But I don't mind having only warning and error for now.

[ruiu]

I'm a bit worried that showing both "error" and "fatal error" might confuse users. They are not different from the users' point of view. "Fatal error" will immediately exit, but "error" will also eventually exit with a failure code. Let's show "error:" for fatal. With that, LGTM.

lld/trunk/ELF/Error.cpp

void elf::log(const Twine &Msg) {
   if (Config->Verbose)
     outs() << Msg << "\n";
 }
 
 void elf::warn(const Twine &Msg) {
   if (Config->FatalWarnings)
     error(Msg);
   else
-    *ErrorOS << Msg << "\n";
+    *ErrorOS << "warning: " << Msg << "\n";
 }
 
 void elf::error(const Twine &Msg) {
-  *ErrorOS << Msg << "\n";
+  *ErrorOS << "error: " << Msg << "\n";
   HasError = true;
 }
 
 void elf::error(std::error_code EC, const Twine &Prefix) {
   error(Prefix + ": " + EC.message());
 }
 
 void elf::fatal(const Twine &Msg) {
-  *ErrorOS << Msg << "\n";
+  *ErrorOS << "error: " << Msg << "\n";
   exit(1);
 }
 
 void elf::fatal(std::error_code EC, const Twine &Prefix) {
   fatal(Prefix + ": " + EC.message());
 }
 
 } // namespace lld

lld/trunk/test/ELF/copy-rel-corrupted.s

 // RUN: llvm-mc %s -o %t.o -filetype=obj -triple=x86_64-pc-linux
 // RUN: llvm-mc %p/Inputs/copy-rel-corrupted.s -o %t2.o -filetype=obj -triple=x86_64-pc-linux
 // RUN: ld.lld %t2.o -o %t2.so -shared
-// RUN: not ld.lld %t.o %t2.so -o %t.exe 2>&1 | FileCheck %s
+// RUN: not ld.lld %t.o %t2.so -o %t.exe 2>&1 | FileCheck %s --match-full-lines
 
-// CHECK: cannot create a copy relocation for symbol x
+// CHECK: error: cannot create a copy relocation for symbol x
 
 .global _start
 _start:
         call x

lld/trunk/test/ELF/entry.s

 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1
 
 # RUN: ld.lld -e foobar %t1 -o %t2 2>&1 | FileCheck -check-prefix=WARN %s
 # RUN: llvm-readobj -file-headers %t2 | FileCheck -check-prefix=NOENTRY %s
-# RUN: ld.lld %t1 -o %t2 2>&1 | FileCheck -check-prefix=WARN2 %s
+# RUN: ld.lld %t1 -o %t2 2>&1 | FileCheck -check-prefix=WARN2 %s --match-full-lines
 
-# RUN: ld.lld -shared -e foobar %t1 -o %t2 2>&1 | FileCheck -check-prefix=WARN %s
+# RUN: ld.lld -shared -e foobar %t1 -o %t2 2>&1 | FileCheck -check-prefix=WARN --match-full-lines %s
 # RUN: ld.lld -shared --fatal-warnings -e entry %t1 -o %t2
 # RUN: ld.lld -shared --fatal-warnings %t1 -o %t2
 
 # RUN: ld.lld %t1 -o %t2 -e entry
 # RUN: llvm-readobj -file-headers %t2 | FileCheck -check-prefix=SYM %s
 # RUN: ld.lld %t1 --fatal-warnings -shared -o %t2 -e entry
 # RUN: llvm-readobj -file-headers %t2 | FileCheck -check-prefix=DSO %s
 # RUN: ld.lld %t1 -o %t2 --entry=4096
 # RUN: llvm-readobj -file-headers %t2 | FileCheck -check-prefix=DEC %s
 # RUN: ld.lld %t1 -o %t2 --entry 0xcafe
 # RUN: llvm-readobj -file-headers %t2 | FileCheck -check-prefix=HEX %s
 # RUN: ld.lld %t1 -o %t2 -e 0777
 # RUN: llvm-readobj -file-headers %t2 | FileCheck -check-prefix=OCT %s
 
-# WARN: entry symbol foobar not found, assuming 0
-# WARN2: entry symbol _start not found, assuming 0
+# WARN: warning: entry symbol foobar not found, assuming 0
+# WARN2: warning: entry symbol _start not found, assuming 0
 
 # NOENTRY: Entry: 0x0
 # SYM: Entry: 0x11000
 # DSO: Entry: 0x1000
 # DEC: Entry: 0x1000
 # HEX: Entry: 0xCAFE
 # OCT: Entry: 0x1FF
 
 .globl entry
 entry:

lld/trunk/test/ELF/linkerscript/diagnostic.s

 # RUN: echo "UNKNOWN_TAG {" > %t.script
 # RUN: echo ".text : { *(.text) }" >> %t.script
 # RUN: echo ".keep : { *(.keep) }" >> %t.script
 # RUN: echo ".temp : { *(.temp) } }" >> %t.script
 # RUN: not ld.lld -shared %t -o %t1 --script %t.script > %t.log 2>&1
 # RUN: FileCheck -check-prefix=ERR6 %s < %t.log
 # ERR6:      line 1:
 # ERR6-NEXT: UNKNOWN_TAG {
-# RUN: grep '^^' %t.log
+# RUN: grep '^error: ^' %t.log
 
 ## One more check that text of lines and pointer to 'bad' token are working ok.
 # RUN: echo "SECTIONS {" > %t.script
 # RUN: echo ".text : { *(.text) }" >> %t.script
 # RUN: echo ".keep : { *(.keep) }" >> %t.script
 # RUN: echo "boom .temp : { *(.temp) } }" >> %t.script
 # RUN: not ld.lld -shared %t -o %t1 --script %t.script > %t.log 2>&1
 # RUN: FileCheck -check-prefix=ERR7 %s < %t.log
 # ERR7:      line 4: malformed number: .temp
 # ERR7-NEXT: boom .temp : { *(.temp) } }
-# RUN: grep '^     ^' %t.log
+# RUN: grep '^error:      ^' %t.log