Add cpp2:: to "did you mean" hints, closes #431

And addresses b979d19#r115739764

Author: hsutter

include/cpp2util.h

@@ -201,6 +201,7 @@
     #include <type_traits>
     #include <new>
     #include <memory>
+    #include <tuple>
     #include <string>
     #include <string_view>
     #include <vector>

regression-tests/test-results/pure2-cpp1-multitoken-fundamental-types-error.cpp2.output

@@ -1,29 +1,29 @@
 pure2-cpp1-multitoken-fundamental-types-error.cpp2...
-pure2-cpp1-multitoken-fundamental-types-error.cpp2(3,8): error: 'signed short int' - did you mean 'short'?
+pure2-cpp1-multitoken-fundamental-types-error.cpp2(3,8): error: 'signed short int' - did you mean cpp2::'short'?
 pure2-cpp1-multitoken-fundamental-types-error.cpp2(3,8): error: 'signed short int' is an old-style C/C++ multi-word keyword type
     - most such types should be used only for interoperability with older code
     - using those when you need them is fine, but name them with these short names instead:
         short, ushort, int, uint, long, ulong, longlong, ulonglong, longdouble, __schar, __uchar
     - see also cpp2util.h > "Convenience names for integer types"
-pure2-cpp1-multitoken-fundamental-types-error.cpp2(4,8): error: 'short int signed' - did you mean 'short'?
+pure2-cpp1-multitoken-fundamental-types-error.cpp2(4,8): error: 'short int signed' - did you mean cpp2::'short'?
 pure2-cpp1-multitoken-fundamental-types-error.cpp2(4,8): error: 'short int signed' is an old-style C/C++ multi-word keyword type
     - most such types should be used only for interoperability with older code
     - using those when you need them is fine, but name them with these short names instead:
         short, ushort, int, uint, long, ulong, longlong, ulonglong, longdouble, __schar, __uchar
     - see also cpp2util.h > "Convenience names for integer types"
-pure2-cpp1-multitoken-fundamental-types-error.cpp2(5,8): error: 'long long unsigned int' - did you mean 'ulonglong'?
+pure2-cpp1-multitoken-fundamental-types-error.cpp2(5,8): error: 'long long unsigned int' - did you mean cpp2::'ulonglong'?
 pure2-cpp1-multitoken-fundamental-types-error.cpp2(5,8): error: 'long long unsigned int' is an old-style C/C++ multi-word keyword type
     - most such types should be used only for interoperability with older code
     - using those when you need them is fine, but name them with these short names instead:
         short, ushort, int, uint, long, ulong, longlong, ulonglong, longdouble, __schar, __uchar
     - see also cpp2util.h > "Convenience names for integer types"
-pure2-cpp1-multitoken-fundamental-types-error.cpp2(6,8): error: 'long double' - did you mean 'long'?
+pure2-cpp1-multitoken-fundamental-types-error.cpp2(6,8): error: 'long double' - did you mean cpp2::'long'?
 pure2-cpp1-multitoken-fundamental-types-error.cpp2(6,8): error: 'long double' is an old-style C/C++ multi-word keyword type
     - most such types should be used only for interoperability with older code
     - using those when you need them is fine, but name them with these short names instead:
         short, ushort, int, uint, long, ulong, longlong, ulonglong, longdouble, __schar, __uchar
     - see also cpp2util.h > "Convenience names for integer types"
-pure2-cpp1-multitoken-fundamental-types-error.cpp2(7,8): error: 'unsigned char' - did you mean 'u8' (usually best) or '__uchar'?
+pure2-cpp1-multitoken-fundamental-types-error.cpp2(7,8): error: 'unsigned char' - did you mean cpp2::'u8' (usually best) or '__uchar'?
 pure2-cpp1-multitoken-fundamental-types-error.cpp2(7,8): error: 'unsigned char' is an old-style C/C++ multi-word keyword type
     - most such types should be used only for interoperability with older code
     - using those when you need them is fine, but name them with these short names instead:

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.2.1   Build 8529:1625
+cppfront compiler v0.2.1   Build 8531:1630
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

source/build.info

@@ -1 +1 @@
-"8529:1625"
+"8531:1630"

source/lex.h

@@ -669,7 +669,7 @@ auto lex_line(
             if (std::ssize(alt) > 0) {
                 errors.emplace_back(
                     pos,
-                    "'" + tokens.back().to_string(true) + "' - did you mean " + alt + "?"
+                    "'" + tokens.back().to_string(true) + "' - did you mean cpp2::" + alt + "?"
                 );
             }
             errors.emplace_back(
@@ -1665,7 +1665,7 @@ auto lex_line(
                     if (tokens.back() == "static_cast") {
                         errors.emplace_back(
                             source_position(lineno, i),
-                            "'static_cast<T>(val)' is not supported in Cpp2 - use 'val as T' for safe conversions instead, or if necessary unsafe_narrow<T>(val) for a possibly-lossy narrowing conversion"
+                            "'static_cast<T>(val)' is not supported in Cpp2 - use 'val as T' for safe conversions instead, or if necessary cpp2::unsafe_narrow<T>(val) for a possibly-lossy narrowing conversion"
                         );
                     }
                     if (tokens.back() == "dynamic_cast") {