> On Nov 11, 2017, at 2:59 PM, Mohammed Ennabah via swift-dev
> <swift-dev@swift.org> wrote:
>
> I dug into the codebase as stated in the steps you mentioned, and tried to
> change one of the errors to see if it really change when I use Swift REPL,
> but nothing changed. Is it possible that I change something and directly
> affect the Swift compiler? (maybe I need to do a build first? Or maybe
> related to xcode-select?)
If you just type "swift" at the command line, you'll run the version of Swift
built into Xcode. You will need to build Swift first ("utils/build-script" is
the easiest way, but not the fastest), and you will also need to run the
version of the Swift interpreter you just built. You can do that with a command
like:
../build/Ninja-DebugAssert/swift-macosx-x86_64/bin/swift
(The path will be a little different if you use the "-x" flag to build-script,
which generates an Xcode project, albeit one that's a pain to use.)
> Each type of diagnostics has 4 parts, ERROR(ID,Options,Text,Signature).
> Diagnostics use the first 3 parts and pass parentheses to the signature. What
> is meant by the signature and why it’s used?
Error messages actually use a sort of format string language similar to
printf(); for those messages which take parameters, the signature gives their
types. For example, DiagnosticsParse.def includes this error:
ERROR(expected_identifier_in_decl,none,
"expected identifier in %0 declaration", (StringRef))
So code which emits that error must include a string to put in place of the
"%0" token:
// When we write "import" followed by a keyword that isn't "class",
"struct", "protocol", etc.:
diagnose(Tok, diag::expected_identifier_in_decl, "import");
// When we try to parse an identifier after e.g. "typealias" and don't
find one:
P.diagnose(P.Tok, diag::expected_identifier_in_decl, DeclKindName);
// When we try to parse an identifier after "case" and find some
punctuation or a literal:
diagnose(CaseLoc, diag::expected_identifier_in_decl, "enum 'case'");
Strings are the most common kind of parameter, but you can also pass other
types and choose between different wordings based on them. For instance, here's
a fix-it note I added for multiline string literals which takes a boolean to
indicate singular or plural:
NOTE(lex_multiline_string_indent_change_line,none,
"change indentation of %select{this line|these lines}0 to match
closing delimiter", (bool))
This error, which is shown when there's a non-digit in an integer literal,
takes both a string containing the bad character, and a number (0 to 3)
indicating which literal format it was parsing:
ERROR(lex_invalid_digit_in_int_literal,none,
"'%0' is not a valid %select{binary digit (0 or 1)|octal digit
(0-7)|"
"digit|hexadecimal digit (0-9, A-F)}1 in integer literal",
(StringRef, unsigned))
If you look around that file and the other Diagnostics*.def files, you'll see
some other interesting examples. Have fun poking around!
--
Brent Royal-Gordon
Architechies
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