Fix remaining cases in #1163, and systematically early-return when an error is detected

Closes #1163

The three remaining cases were lack of backtracking after refusing to parse `: name *` with the helpful error about the Cpp1-style pointer declaration being invalid

But also more generally: Several recent ICE/ASAN bug reports, including the first two in #1163, have been because of trying to continue lexing/parsing for a bit after an error was identified, so I also went through to systematically ensure every time we record an error we (a) early-return and (b) don't do next() since there should be no point... (a) is the main improvement, (b) is just hygiene but probably has no effect. This change only changes the output of two regression test cases, and both are improvements.

Author: hsutter

Diff for: regression-tests/test-results/pure2-return-tuple-no-identifier-error.cpp2.output

@@ -1,4 +1,4 @@
 pure2-return-tuple-no-identifier-error.cpp2...
 pure2-return-tuple-no-identifier-error.cpp2(1,11): error: expected identifier, not 'int'
-pure2-return-tuple-no-identifier-error.cpp2(1,16): error: expected identifier, not 'int'
+pure2-return-tuple-no-identifier-error.cpp2(1,14): error: missing function return after -> (at ',')
 

Diff for: regression-tests/test-results/pure2-return-tuple-no-type-error.cpp2.output

@@ -1,4 +1,4 @@
 pure2-return-tuple-no-type-error.cpp2...
 pure2-return-tuple-no-type-error.cpp2(1,11): error: return parameter 'a' must have a type
-pure2-return-tuple-no-type-error.cpp2(1,14): error: return parameter 'b' must have a type
+pure2-return-tuple-no-type-error.cpp2(1,12): error: missing function return after -> (at ',')
 

Diff for: regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.7.1   Build 9715:1649
+cppfront compiler v0.7.1   Build 9716:1345
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

Diff for: source/build.info

@@ -1 +1 @@
-"9715:1649"
+"9716:1345"

Diff for: source/io.h

@@ -779,6 +779,7 @@ auto process_cpp2_line(
                                 " after the closing ; or } of a definition, the rest"
                                 " of the line cannot begin a /*...*/ comment")
                         );
+                        return false;
                     }
                 }
 
@@ -807,6 +808,7 @@ auto process_cpp2_line(
             source_position(lineno, unsafe_narrow<colno_t>(ssize(line))),
             std::string("line ended before character literal was terminated")
         );
+        return false;
     }
 
     return found_end;

Diff for: source/lex.h

@@ -751,6 +751,8 @@ auto lex_line(
                 "        short, ushort, int, uint, long, ulong, longlong, ulonglong, longdouble, _schar, _uchar\n"
                 "    - see also cpp2util.h > \"Convenience names for integer types\""
             );
+
+            return;
         }
 
         tokens.push_back(last_token);
@@ -1002,6 +1004,7 @@ auto lex_line(
                 "invalid universal character name - \\u without { must"
                 " be followed by 4 hexadecimal digits"
             );
+            return 0;
         }
 
         else if (
@@ -1022,15 +1025,16 @@ auto lex_line(
 
             if (peek(j + offset) == '}') {
                 ++j;
+                return j;
             }
             else {
                 errors.emplace_back(
                     source_position(lineno, i + offset),
                     "invalid universal character name - \\u{ must"
                     " be followed by hexadecimal digits and a closing }"
                 );
+                return 0;
             }
-            return j;
         }
 
         else if (
@@ -1052,7 +1056,9 @@ auto lex_line(
                 "invalid universal character name - \\U must"
                     " be followed by 8 hexadecimal digits"
             );
+            return 0;
         }
+
         return 0;
     };
 
@@ -1535,6 +1541,7 @@ auto lex_line(
                             "invalid new-line in raw string delimiter \"" + line.substr(i, 3)
                                 + "\" - stray 'R' in program \""
                         );
+                        return {};
                     }
                 } else {
                     store(1, lexeme::Dollar);
@@ -1579,6 +1586,7 @@ auto lex_line(
                             source_position(lineno, i),
                             "binary literal cannot be empty (0B must be followed by binary digits)"
                         );
+                        return {};
                     }
                 }
                 else if (peek1 == 'x' || peek1 == 'X') {
@@ -1592,6 +1600,7 @@ auto lex_line(
                             source_position(lineno, i),
                             "hexadecimal literal cannot be empty (0X must be followed by hexadecimal digits)"
                         );
+                        return {};
                     }
                 }
             }
@@ -1658,6 +1667,7 @@ auto lex_line(
                                     source_position(lineno, i),
                                     "a floating point literal must have at least one digit after the decimal point (can be '.0')"
                                 );
+                                return {};
                             }
                             while (is_separator_or(is_digit,peek(j))) {
                                 ++j;
@@ -1725,6 +1735,7 @@ auto lex_line(
                                 "invalid new-line in raw string delimiter \"" + line.substr(i, j)
                                     + "\" - stray 'R' in program \""
                             );
+                            return {};
                         }
                     }
                     else {
@@ -1783,6 +1794,7 @@ auto lex_line(
                                 "character literal '" + line.substr(i+1, j-1)
                                     + "' is missing its closing '"
                             );
+                            return {};
                         }
                         store(j+1, lexeme::CharacterLiteral);
                     }
@@ -1791,6 +1803,7 @@ auto lex_line(
                             source_position(lineno, i),
                             "character literal is empty"
                         );
+                        return {};
                     }
                 }
 
@@ -1816,18 +1829,21 @@ auto lex_line(
                             source_position(lineno, i),
                             "'const_cast' is not supported in Cpp2 - the current C++ best practice is to never cast away const, and that is const_cast's only effective use"
                         );
+                        return {};
                     }
                     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 cpp2::unsafe_narrow<T>(val) for a possibly-lossy narrowing conversion"
                         );
+                        return {};
                     }
                     if (tokens.back() == "dynamic_cast") {
                         errors.emplace_back(
                             source_position(lineno, i),
                             "'dynamic_cast<Derived*>(pBase)' is not supported in Cpp2 - use 'pBase as *Derived' for safe dynamic conversions instead"
                         );
+                        return {};
                     }
                 }
 
@@ -1854,12 +1870,14 @@ auto lex_line(
                                 source_position(lineno, i),
                                 "'NULL' is not supported in Cpp2 - for a local pointer variable, leave it uninitialized instead, and set it to a non-null value when you have one"
                             );
+                            return {};
                         }
                         if (tokens.back() == "delete") {
                             errors.emplace_back(
                                 source_position(lineno, i),
                                 "'delete' and owning raw pointers are not supported in Cpp2 - use unique.new<T> or shared.new<T> instead in that order (or, in the future, gc.new<T>, but that is not yet implemented)"
                             );
+                            return {};
                         }
                     }
                 }
@@ -1873,6 +1891,7 @@ auto lex_line(
                         false,
                         true    // a noisy fallback error message
                     );
+                    return {};
                 }
             }
         }