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fmt/Printf: document and tweak error messages produced for bad formats
R=golang-dev, adg CC=golang-dev https://golang.org/cl/2198044
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@ -69,8 +69,8 @@
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Regardless of the verb, if an operand is an interface value,
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the internal concrete value is used, not the interface itself.
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Thus:
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var i interface{} = 23;
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fmt.Printf("%v\n", i);
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var i interface{} = 23
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fmt.Printf("%v\n", i)
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will print 23.
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If an operand implements interface Formatter, that interface
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@ -85,6 +85,26 @@
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cast the value before recurring:
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func (x X) String() string { return Sprintf("%d", int(x)) }
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Format errors:
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If an invalid argument is given for a verb, such as providing
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a string to %d, the generated string will contain a
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description of the problem, as in these examples:
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Wrong type or unknown verb: %!verb(type=value)
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Printf("%d", hi): %!d(string=hi)
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Too many arguments: %!(EXTRA type=value)
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Printf("hi", "guys"): hi%!(EXTRA string=guys)
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Too few arguments: %!verb(MISSING)
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Printf("hi%d"): hi %!d(MISSING)
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Non-int for width or precision: %!(BADWIDTH) or %!(BADPREC)
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Printf("%*s", 4.5, "hi"): %!(BADWIDTH)hi
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Printf("%.*s", 4.5, "hi"): %!(BADPREC)hi
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All errors begin with the string "%!" followed sometimes
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by a single character (the verb) and end with a parenthesized
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description.
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Scanning:
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An analogous set of functions scans formatted text to yield
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@ -97,7 +117,7 @@
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routines treat newlines as spaces.
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Scanf, Fscanf, and Sscanf parse the arguments according to a
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format string, analogous to that of Printf. For example, "%x"
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format string, analogous to that of Printf. For example, %x
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will scan an integer as a hexadecimal number, and %v will scan
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the default representation format for the value.
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@ -193,8 +193,8 @@ var fmttests = []fmtTest{
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fmtTest{"%+.3g", complex128(1 + 2i), "(+1+2i)"},
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// erroneous formats
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fmtTest{"", 2, "?(extra int=2)"},
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fmtTest{"%d", "hello", "%d(string=hello)"},
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fmtTest{"", 2, "%!(EXTRA int=2)"},
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fmtTest{"%d", "hello", "%!d(string=hello)"},
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// old test/fmt_test.go
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fmtTest{"%d", 1234, "1234"},
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@ -301,7 +301,7 @@ var fmttests = []fmtTest{
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fmtTest{"%s", I(23), `<23>`},
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fmtTest{"%q", I(23), `"<23>"`},
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fmtTest{"%x", I(23), `3c32333e`},
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fmtTest{"%d", I(23), `%d(string=<23>)`},
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fmtTest{"%d", I(23), `%!d(string=<23>)`},
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// go syntax
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fmtTest{"%#v", A{1, 2, "a", []int{1, 2}}, `fmt_test.A{i:1, j:0x2, s:"a", x:[]int{1, 2}}`},
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@ -321,7 +321,7 @@ var fmttests = []fmtTest{
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// renamings
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fmtTest{"%v", renamedBool(true), "true"},
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fmtTest{"%d", renamedBool(true), "%d(fmt_test.renamedBool=true)"},
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fmtTest{"%d", renamedBool(true), "%!d(fmt_test.renamedBool=true)"},
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fmtTest{"%o", renamedInt(8), "10"},
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fmtTest{"%d", renamedInt8(-9), "-9"},
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fmtTest{"%v", renamedInt16(10), "10"},
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@ -366,14 +366,14 @@ var fmttests = []fmtTest{
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fmtTest{"%p", make(chan int), "PTR"},
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fmtTest{"%p", make(map[int]int), "PTR"},
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fmtTest{"%p", make([]int, 1), "PTR"},
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fmtTest{"%p", 27, "%p(int=27)"}, // not a pointer at all
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fmtTest{"%p", 27, "%!p(int=27)"}, // not a pointer at all
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// erroneous things
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fmtTest{"%d", "hello", "%d(string=hello)"},
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fmtTest{"no args", "hello", "no args?(extra string=hello)"},
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fmtTest{"%s", nil, "%s(<nil>)"},
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fmtTest{"%d", "hello", "%!d(string=hello)"},
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fmtTest{"no args", "hello", "no args%!(EXTRA string=hello)"},
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fmtTest{"%s", nil, "%!s(<nil>)"},
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fmtTest{"%T", nil, "<nil>"},
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fmtTest{"%-1", 100, "%1(int=100)"},
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fmtTest{"%-1", 100, "%!1(int=100)"},
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}
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func TestSprintf(t *testing.T) {
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@ -622,12 +622,12 @@ var startests = []starTest{
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starTest{"%-*d", args(4, 42), "42 "},
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// erroneous
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starTest{"%*d", args(nil, 42), "%(badwidth)42"},
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starTest{"%.*d", args(nil, 42), "%(badprec)42"},
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starTest{"%*d", args(5, "foo"), "%d(string= foo)"},
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starTest{"%*d", args(nil, 42), "%!(BADWIDTH)42"},
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starTest{"%.*d", args(nil, 42), "%!(BADPREC)42"},
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starTest{"%*d", args(5, "foo"), "%!d(string= foo)"},
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starTest{"%*% %d", args(20, 5), "% 5"},
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starTest{"%*", args(4), "%(badwidth)%*(int=4)"},
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starTest{"%*d", args(int32(4), 42), "%(badwidth)42"},
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starTest{"%*", args(4), "%!(BADWIDTH)%!*(int=4)"},
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starTest{"%*d", args(int32(4), 42), "%!(BADWIDTH)42"},
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}
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// TODO: there's no conversion from []T to ...T, but we can fake it. These
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@ -20,12 +20,12 @@ var (
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nilParenBytes = []byte("(nil)")
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nilBytes = []byte("nil")
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mapBytes = []byte("map[")
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missingBytes = []byte("missing")
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extraBytes = []byte("?(extra ")
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missingBytes = []byte("(MISSING)")
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extraBytes = []byte("%!(EXTRA ")
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irparenBytes = []byte("i)")
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bytesBytes = []byte("[]byte{")
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widthBytes = []byte("%(badwidth)")
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precBytes = []byte("%(badprec)")
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widthBytes = []byte("%!(BADWIDTH)")
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precBytes = []byte("%!(BADPREC)")
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)
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// State represents the printer state passed to custom formatters.
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@ -266,6 +266,7 @@ func (p *pp) unknownType(v interface{}) {
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func (p *pp) badVerb(verb int, val interface{}) {
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p.add('%')
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p.add('!')
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p.add(verb)
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p.add('(')
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if val == nil {
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