Add formatting for source_location.

nth/debug/BUILD

@@ -27,6 +27,8 @@ cc_library(
     name = "source_location",
     hdrs = ["source_location.h"],
     deps = [
+        "//nth/format",
+        "//nth/io/writer",
         "//nth/utility:unconstructible",
     ],
 )
@@ -36,6 +38,8 @@ cc_test(
     srcs = ["source_location_test.cc"],
     deps = [
         ":source_location",
+        "//nth/format",
+        "//nth/io/writer:string",
     ],
 )
 

nth/debug/source_location.h

@@ -3,6 +3,8 @@
 
 #include <string_view>
 
+#include "nth/format/format.h"
+#include "nth/io/writer/writer.h"
 #include "nth/utility/unconstructible.h"
 
 namespace nth {
@@ -38,6 +40,13 @@ struct source_location {
   // Returns the line number corresponding to this source location.
   constexpr unsigned line() const { return line_; }
 
+  friend void NthFormat(auto& w, auto&, nth::source_location loc) {
+    nth::io::write_text(w, loc.file_);
+    nth::io::write_text(w, ":");
+    auto fmt = nth::default_formatter<unsigned>();
+    nth::format(w, fmt, loc.line_);
+  }
+
  private:
   explicit constexpr source_location(char const* file, char const* function,
                                      unsigned line)

nth/debug/source_location_test.cc

@@ -1,5 +1,8 @@
 #include "nth/debug/source_location.h"
 
+#include "nth/format/format.h"
+#include "nth/io/writer/string.h"
+
 namespace some_namespace {
 
 static_assert([] {
@@ -35,4 +38,13 @@ static_assert([] {
 
 }  // namespace some_namespace
 
-int main() { return 0; }
+int main() {
+#line 30 "some_file.cc"
+  nth::source_location loc = nth::source_location::current();
+  std::string s;
+  nth::io::string_writer w(s);
+  nth::format(w, loc);
+  if (s != "some_file.cc:31") return 1;
+
+  return 0;
+}