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* Added a new kind of multi-line string literal delimited by two

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single quotes.  Example (from NixOS):

    job = ''
      start on network-interfaces

      start script

        rm -f /var/run/opengl-driver
        ${if videoDriver == "nvidia"        
          then "ln -sf ${nvidiaDrivers} /var/run/opengl-driver"
          else if cfg.driSupport
          then "ln -sf ${mesa} /var/run/opengl-driver"
          else ""
        }

        rm -f /var/log/slim.log

      end script
    '';

  This style has two big advantages:

  - \, ' and " aren't special, only '' and ${.  So you get a lot less
    escaping in shell scripts / configuration files in Nixpkgs/NixOS.
    The delimiter '' is rare in scripts (and can usually be written as
    "").  ${ is also fairly rare.

    Other delimiters such as <<...>>, {{...}} and <|...|> were also
    considered but this one appears to have the fewest drawbacks
    (thanks Martin).

  - Indentation is intelligently stripped so that multi-line strings
    can follow the nesting structure of the containing Nix
    expression.  E.g. in the example above 6 spaces are stripped from
    the start of each line.  This prevents unnecessary indentation in
    generated files (which sometimes even breaks things).

  See tests/lang/eval-okay-ind-string.nix for some examples.
This commit is contained in:
Eelco Dolstra 2007-11-30 16:48:45 +00:00
parent 633518628f
commit 6d6c68c0d2
6 changed files with 235 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

15
src/libexpr/lexer.l
View file

@ -4,6 +4,7 @@
%x STRING
%x IND_STRING
%{
@ -122,6 +123,14 @@ inherit { return INHERIT; }
<STRING>\" { BEGIN(INITIAL); return '"'; }
<STRING>. return yytext[0]; /* just in case: shouldn't be reached */
\'\'(\ *\n)? { BEGIN(IND_STRING); return IND_STRING_OPEN; }
<IND_STRING>([^\$\']|\$[^\{\']|\'[^\'])+ {
yylval->t = makeIndStr(toATerm(yytext));
return IND_STR;
}
<IND_STRING>\$\{ { BEGIN(INITIAL); return DOLLAR_CURLY; }
<IND_STRING>\'\' { BEGIN(INITIAL); return IND_STRING_CLOSE; }
<IND_STRING>. return yytext[0]; /* just in case: shouldn't be reached */
{PATH} { yylval->t = toATerm(yytext); return PATH; /* !!! alloc */ }
{URI} { yylval->t = toATerm(yytext); return URI; /* !!! alloc */ }
@ -148,4 +157,10 @@ void backToString(yyscan_t scanner)
BEGIN(STRING);
}
void backToIndString(yyscan_t scanner)
{
struct yyguts_t * yyg = (struct yyguts_t *) scanner;
BEGIN(IND_STRING);
}
}

3
src/libexpr/nixexpr-ast.def
View file

@ -46,6 +46,9 @@ Int | int | Expr |
Str | string ATermList | Expr |
Str | string | Expr | ObsoleteStr
# Internal to the parser, doesn't occur in ASTs.
IndStr | string | Expr |
# A path is a reference to a file system object that is to be copied
# to the Nix store when used as a derivation attribute. When it is
# concatenated to a string (i.e., `str + path'), it is also copied and

109
src/libexpr/parser.y
View file

@ -68,9 +68,100 @@ static Expr fixAttrs(int recursive, ATermList as)
}
void backToString(yyscan_t scanner);
static Expr stripIndentation(ATermList es)
{
if (es == ATempty) return makeStr("");
/* Figure out the minimum indentation. Note that by design
whitespace-only final lines are not taken into account. (So
the " " in "\n ''" is ignored, but the " " in "\n foo''" is.) */
bool atStartOfLine = true; /* = seen only whitespace in the current line */
unsigned int minIndent = 1000000;
unsigned int curIndent = 0;
ATerm e;
for (ATermIterator i(es); i; ++i) {
if (!matchIndStr(*i, e)) {
/* Anti-quotations end the current start-of-line whitespace. */
if (atStartOfLine) {
atStartOfLine = false;
if (curIndent < minIndent) minIndent = curIndent;
}
continue;
}
string s = aterm2String(e);
for (unsigned int j = 0; j < s.size(); ++j) {
if (atStartOfLine) {
if (s[j] == ' ')
curIndent++;
else if (s[j] == '\n') {
/* Empty line, doesn't influence minimum
indentation. */
curIndent = 0;
} else {
atStartOfLine = false;
if (curIndent < minIndent) minIndent = curIndent;
}
} else if (s[j] == '\n') {
atStartOfLine = true;
curIndent = 0;
}
}
}
/* Strip spaces from each line. */
ATermList es2 = ATempty;
atStartOfLine = true;
unsigned int curDropped = 0;
unsigned int n = ATgetLength(es);
for (ATermIterator i(es); i; ++i, --n) {
if (!matchIndStr(*i, e)) {
atStartOfLine = false;
curDropped = 0;
es2 = ATinsert(es2, *i);
continue;
}
string s = aterm2String(e);
string s2;
for (unsigned int j = 0; j < s.size(); ++j) {
if (atStartOfLine) {
if (s[j] == ' ') {
if (curDropped++ >= minIndent)
s2 += s[j];
}
else if (s[j] == '\n') {
curDropped = 0;
s2 += s[j];
} else {
atStartOfLine = false;
curDropped = 0;
s2 += s[j];
}
} else {
s2 += s[j];
if (s[j] == '\n') atStartOfLine = true;
}
}
/* Remove the last line if it is empty and consists only of
spaces. */
if (n == 1) {
unsigned int p = s2.find_last_of('\n');
if (p != string::npos && s2.find_first_not_of(' ', p + 1) == string::npos)
s2 = string(s2, 0, p + 1);
}
es2 = ATinsert(es2, makeStr(s2));
}
return makeConcatStrings(ATreverse(es2));
}
void backToString(yyscan_t scanner);
void backToIndString(yyscan_t scanner);
static Pos makeCurPos(YYLTYPE * loc, ParseData * data)
{
return makePos(toATerm(data->path),
@ -121,10 +212,11 @@ static void freeAndUnprotect(void * p)
%type <t> start expr expr_function expr_if expr_op
%type <t> expr_app expr_select expr_simple bind inheritsrc formal
%type <ts> binds ids expr_list formals string_parts
%token <t> ID INT STR PATH URI
%type <ts> binds ids expr_list formals string_parts ind_string_parts
%token <t> ID INT STR IND_STR PATH URI
%token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL
%token DOLLAR_CURLY /* == ${ */
%token IND_STRING_OPEN IND_STRING_CLOSE
%nonassoc IMPL
%left OR
@ -199,6 +291,9 @@ expr_simple
else if (ATgetNext($2) == ATempty) $$ = ATgetFirst($2);
else $$ = makeConcatStrings(ATreverse($2));
}
| IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
$$ = stripIndentation(ATreverse($2));
}
| PATH { $$ = makePath(toATerm(absPath(aterm2String($1), data->basePath))); }
| URI { $$ = makeStr($1, ATempty); }
| '(' expr ')' { $$ = $2; }
@ -219,6 +314,12 @@ string_parts
| { $$ = ATempty; }
;
ind_string_parts
: ind_string_parts IND_STR { $$ = ATinsert($1, $2); }
| ind_string_parts DOLLAR_CURLY expr '}' { backToIndString(scanner); $$ = ATinsert($1, $3); }
| { $$ = ATempty; }
;
binds
: binds bind { $$ = ATinsert($1, $2); }
| { $$ = ATempty; }