Special-case paths that appear in libs by not prefixing them with -l.

tools/gn/variables.cc

Index: tools/gn/variables.cc
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index d79c3aa887defcdf0101ab393ca6099bd7c71b3b..1e886dd71cd18a96d6c0b0e6ae502ba9ae2e085e 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -892,9 +892,12 @@ const char kLibs_HelpShort[] =
 const char kLibs_Help[] =
     "libs: Additional libraries to link.\n"
     "\n"
-    "  A list of strings.\n"
+    "  A list of library names or library paths.\n"
+    "\n"
+    "  Values containing '/' will be treated as paths, and those without will\n"
+    "  be treated as library names."
     "\n"
-    "  These files will be passed to the linker, which will generally search\n"
+    "  Names will be passed to the linker, which will generally search\n"
     "  the library include path. Unlike a normal list of files, they will be\n"
     "  passed to the linker unmodified rather than being treated as file\n"
     "  names relative to the current build file. Generally you would set\n"
@@ -904,8 +907,8 @@ const char kLibs_Help[] =
     "\n"
     "  When constructing the linker command, the \"lib_prefix\" attribute of\n"
     "  the linker tool in the current toolchain will be prepended to each\n"
-    "  library. So your BUILD file should not specify the switch prefix\n"
-    "  (like \"-l\").\n"
+    "  library name (but not library paths). Your BUILD file should not\n"

[brettw, 2015/12/18 00:04:55]

How about replacing the existing docs with:

Values containing '/' will be treated as references to files in the build. They
will be rebased to be relative to the build directory and specified in the
\"libs\" for linker tools. This facility should be used for libraries that are
checked in to the build. For libraries that are generated by the build, use
normal GN deps to link them.

Values not containing '/' will be treated as system library names. These will be
passed unmodified to the linker and prefixed with the \"lib_prefix\" attribute
of the linker tool. Generally you would set the \"lib_dirs\" so the given
library is found. Your BUILD.gn file should not specify the switch prefix (like
\"-l\"): this will be encoded in the \"lib_prefix\" of the tool.

...framework exception paragraph...

[agrieve, 2015/12/18 15:39:08]

Sounds great! Done.

+    "  specify the switch prefix (like \"-l\").\n"
     "\n"
     "  Libraries ending in \".framework\" will be special-cased: the switch\n"
     "  \"-framework\" will be prepended instead of the lib_prefix, and the\n"