patch 9.0.1704: Cannot use positional arguments for printf()

Problem: Cannot use positional arguments for printf()
Solution: Support positional arguments in string formatting

closes: #12140

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Christ van Willegen <cvwillegen@gmail.com>

runtime/doc/builtin.txt

@@ -6590,7 +6590,11 @@ printf({fmt}, {expr1} ...)				*printf()*
 		The "%" starts a conversion specification.  The following
 		arguments appear in sequence:
 
-			%  [flags]  [field-width]  [.precision]  type
+			% [pos-argument] [flags] [field-width] [.precision] type
+
+		pos-argument
+			At most one positional argument specifier. These
+			take the form {n$}, where n is >= 1.
 
 		flags
 			Zero or more of the following flags:
@@ -6662,6 +6666,13 @@ printf({fmt}, {expr1} ...)				*printf()*
 <		This limits the length of the text used from "line" to
 		"width" bytes.
 
+		If the argument to be formatted is specified using a posional
+		argument specifier, and a '*' is used to indicate that a
+		number argument is to be used to specify the width or
+		precision, the argument(s) to be used must also be specified
+		using a {n$} positional argument specifier. See |printf-$|.
+
+
 		The conversion specifiers and their meanings are:
 
 				*printf-d* *printf-b* *printf-B* *printf-o*
@@ -6751,6 +6762,103 @@ printf({fmt}, {expr1} ...)				*printf()*
 		of "%" items.  If there are not sufficient or too many
 		arguments an error is given.  Up to 18 arguments can be used.
 
+							*printf-$*
+		In certain languages, error and informative messages are
+		more readable when the order of words is different from the
+		corresponding message in English. To accomodate translations
+		having a different word order, positional arguments may be
+		used to indicate this. For instance: >
+
+			#, c-format
+			msgid "%s returning %s"
+			msgstr "waarde %2$s komt terug van %1$s"
+<
+		In this example, the sentence has its 2 string arguments reversed
+		in the output. >
+
+			echo printf(
+				"In The Netherlands, vim's creator's name is: %1$s %2$s",
+				"Bram", "Moolenaar")
+<			In The Netherlands, vim's creator's name is: Bram Moolenaar >
+
+			echo printf(
+				"In Belgium, vim's creator's name is: %2$s %1$s",
+				"Bram", "Moolenaar")
+<			In Belgium, vim's creator's name is: Moolenaar Bram
+
+		Width (and precision) can be specified using the '*' specifier.
+		In this case, you must specify the field width position in the
+		argument list. >
+
+			echo printf("%1$*2$.*3$d", 1, 2, 3)
+<			001 >
+			echo printf("%2$*3$.*1$d", 1, 2, 3)
+<			  2 >
+			echo printf("%3$*1$.*2$d", 1, 2, 3)
+<			03 >
+			echo printf("%1$*2$.*3$g", 1.4142, 2, 3)
+<			1.414
+
+		You can mix specifying the width and/or precision directly
+		and via positional arguments: >
+
+			echo printf("%1$4.*2$f", 1.4142135, 6)
+<			1.414214 >
+			echo printf("%1$*2$.4f", 1.4142135, 6)
+<			1.4142 >
+			echo printf("%1$*2$.*3$f", 1.4142135, 6, 2)
+<			  1.41
+
+							*E1400*
+		You cannot mix positional and non-positional arguments: >
+			echo printf("%s%1$s", "One", "Two")
+<			E1400: Cannot mix positional and non-positional
+			arguments: %s%1$s
+
+							*E1401*
+		You cannot skip a positional argument in a format string: >
+			echo printf("%3$s%1$s", "One", "Two", "Three")
+<			E1401: format argument 2 unused in $-style
+			format: %3$s%1$s
+
+							*E1402*
+		You can re-use a [field-width] (or [precision]) argument: >
+			echo printf("%1$d at width %2$d is: %01$*2$d", 1, 2)
+<			1 at width 2 is: 01
+
+		However, you can't use it as a different type: >
+			echo printf("%1$d at width %2$ld is: %01$*2$d", 1, 2)
+<			E1402: Positional argument 2 used as field
+			width reused as different type: long int/int
+
+							*E1403*
+		When a positional argument is used, but not the correct number
+		or arguments is given, an error is raised: >
+			echo printf("%1$d at width %2$d is: %01$*2$.*3$d", 1, 2)
+<			E1403: Positional argument 3 out of bounds:
+			%1$d at width %2$d is: %01$*2$.*3$d
+
+		Only the first error is reported: >
+			echo printf("%01$*2$.*3$d %4$d", 1, 2)
+<			E1403: Positional argument 3 out of bounds:
+			%01$*2$.*3$d %4$d
+
+							*E1404*
+		A positional argument can be used more than once: >
+			echo printf("%1$s %2$s %1$s", "One", "Two")
+<			One Two One
+
+		However, you can't use a different type the second time: >
+			echo printf("%1$s %2$s %1$d", "One", "Two")
+<			E1404: Positional argument 1 type used
+			inconsistently: int/string
+
+							*E1405*
+		Various other errors that lead to a format string being
+		wrongly formatted lead to: >
+			echo printf("%1$d at width %2$d is: %01$*2$.3$d", 1, 2)
+<			E1405: Invalid format specifier:
+			%1$d at width %2$d is: %01$*2$.3$d
 
 prompt_getprompt({buf})					*prompt_getprompt()*
 		Returns the effective prompt text for buffer {buf}.  {buf} can

src/errors.h

@@ -3477,3 +3477,17 @@ EXTERN char e_incomplete_type[]
 #endif
 EXTERN char e_warning_pointer_block_corrupted[]
 	INIT(= N_("E1364: Warning: Pointer block corrupted"));
+EXTERN char e_cannot_mix_positional_and_non_positional_str[]
+	INIT(= N_("E1400: Cannot mix positional and non-positional arguments: %s"));
+EXTERN char e_fmt_arg_nr_unused_str[]
+	INIT(= N_("E1401: format argument %d unused in $-style format: %s"));
+EXTERN char e_positional_num_field_spec_reused_str_str[]
+	INIT(= N_("E1402: Positional argument %d used as field width reused as different type: %s/%s"));
+EXTERN char e_positional_nr_out_of_bounds_str[]
+	INIT(= N_("E1403: Positional argument %d out of bounds: %s"));
+EXTERN char e_positional_arg_num_type_inconsistent_str_str[]
+	INIT(= N_("E1404: Positional argument %d type used inconsistently: %s/%s"));
+EXTERN char e_invalid_format_specifier_str[]
+	INIT(= N_("E1405: Invalid format specifier: %s"));
+
+// E1365 - E1399 unused

src/globals.h

@@ -1674,6 +1674,19 @@ EXTERN int	cmdwin_result INIT(= 0); // result of cmdline window or 0
 
 EXTERN char_u no_lines_msg[]	INIT(= N_("--No lines in buffer--"));
 
+EXTERN char typename_unknown[]	INIT(= N_("unknown"));
+EXTERN char typename_int[]	INIT(= N_("int"));
+EXTERN char typename_longint[]	INIT(= N_("long int"));
+EXTERN char typename_longlongint[]	INIT(= N_("long long int"));
+EXTERN char typename_unsignedint[]	INIT(= N_("unsigned int"));
+EXTERN char typename_unsignedlongint[]	INIT(= N_("unsigned long int"));
+EXTERN char typename_unsignedlonglongint[]	INIT(= N_("unsigned long long int"));
+EXTERN char typename_pointer[]	INIT(= N_("pointer"));
+EXTERN char typename_percent[]	INIT(= N_("percent"));
+EXTERN char typename_char[] INIT(= N_("char"));
+EXTERN char typename_string[]	INIT(= N_("string"));
+EXTERN char typename_float[]	INIT(= N_("float"));
+
 /*
  * When ":global" is used to number of substitutions and changed lines is
  * accumulated until it's finished.