fmt: add more function and allocation tests

This is part of a series of CLs that aim to reduce how often interface
arguments escape for the print functions in fmt.

Currently, method values are one of two reasons reflect.Value.Interface
always escapes its reflect.Value.

Our later CLs modify behavior around method values, so we add some tests
of function formatting (including method values) to help reduce the
chances of breaking behavior later.

We also add in some allocation tests focused on interface arguments for
the print functions. These currently do not show any improvements
compared to Go 1.21.

These tests were originally in a later CL in our stack (CL 528538),
but we split them out into this CL and moved them earlier in the stack.

Updates #8618

Change-Id: Iec51abc3b7f86a2711e7497fc2fb7a678b9f8f73
Reviewed-on: https://go-review.googlesource.com/c/go/+/529575
Reviewed-by: Carlos Amedee <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: thepudds

src/fmt/fmt_test.go

@@ -11,7 +11,6 @@ import (
 	"io"
 	"math"
 	"reflect"
-	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -112,6 +111,19 @@ func (p *P) String() string {
 	return "String(p)"
 }
 
+// Fn is a function type with a String method.
+type Fn func() int
+
+func (fn Fn) String() string { return "String(fn)" }
+
+var fnValue Fn
+
+// U is a type with two unexported function fields.
+type U struct {
+	u  func() string
+	fn Fn
+}
+
 var barray = [5]renamedUint8{1, 2, 3, 4, 5}
 var bslice = barray[:]
 
@@ -714,7 +726,6 @@ var fmtTests = []struct {
 	// go syntax
 	{"%#v", A{1, 2, "a", []int{1, 2}}, `fmt_test.A{i:1, j:0x2, s:"a", x:[]int{1, 2}}`},
 	{"%#v", new(byte), "(*uint8)(0xPTR)"},
-	{"%#v", TestFmtInterface, "(func(*testing.T))(0xPTR)"},
 	{"%#v", make(chan int), "(chan int)(0xPTR)"},
 	{"%#v", uint64(1<<64 - 1), "0xffffffffffffffff"},
 	{"%#v", 1000000000, "1000000000"},
@@ -737,6 +748,54 @@ var fmtTests = []struct {
 	{"%#v", 1.2345678, "1.2345678"},
 	{"%#v", float32(1.2345678), "1.2345678"},
 
+	// functions
+	{"%v", TestFmtInterface, "0xPTR"}, // simple function
+	{"%v", reflect.ValueOf(TestFmtInterface), "0xPTR"},
+	{"%v", G.GoString, "0xPTR"}, // method expression
+	{"%v", reflect.ValueOf(G.GoString), "0xPTR"},
+	{"%v", G(23).GoString, "0xPTR"}, // method value
+	{"%v", reflect.ValueOf(G(23).GoString), "0xPTR"},
+	{"%v", reflect.ValueOf(G(23)).Method(0), "0xPTR"},
+	{"%v", Fn.String, "0xPTR"}, // method of function type
+	{"%v", reflect.ValueOf(Fn.String), "0xPTR"},
+	{"%v", fnValue, "String(fn)"}, // variable of function type with String method
+	{"%v", reflect.ValueOf(fnValue), "String(fn)"},
+	{"%v", [1]Fn{fnValue}, "[String(fn)]"}, // array of function type with String method
+	{"%v", reflect.ValueOf([1]Fn{fnValue}), "[String(fn)]"},
+	{"%v", fnValue.String, "0xPTR"}, // method value from function type
+	{"%v", reflect.ValueOf(fnValue.String), "0xPTR"},
+	{"%v", reflect.ValueOf(fnValue).Method(0), "0xPTR"},
+	{"%v", U{}.u, "<nil>"}, // unexported function field
+	{"%v", reflect.ValueOf(U{}.u), "<nil>"},
+	{"%v", reflect.ValueOf(U{}).Field(0), "<nil>"},
+	{"%v", U{fn: fnValue}.fn, "String(fn)"}, // unexported field of function type with String method
+	{"%v", reflect.ValueOf(U{fn: fnValue}.fn), "String(fn)"},
+	{"%v", reflect.ValueOf(U{fn: fnValue}).Field(1), "<nil>"},
+
+	// functions with go syntax
+	{"%#v", TestFmtInterface, "(func(*testing.T))(0xPTR)"}, // simple function
+	{"%#v", reflect.ValueOf(TestFmtInterface), "(func(*testing.T))(0xPTR)"},
+	{"%#v", G.GoString, "(func(fmt_test.G) string)(0xPTR)"}, // method expression
+	{"%#v", reflect.ValueOf(G.GoString), "(func(fmt_test.G) string)(0xPTR)"},
+	{"%#v", G(23).GoString, "(func() string)(0xPTR)"}, // method value
+	{"%#v", reflect.ValueOf(G(23).GoString), "(func() string)(0xPTR)"},
+	{"%#v", reflect.ValueOf(G(23)).Method(0), "(func() string)(0xPTR)"},
+	{"%#v", Fn.String, "(func(fmt_test.Fn) string)(0xPTR)"}, // method of function type
+	{"%#v", reflect.ValueOf(Fn.String), "(func(fmt_test.Fn) string)(0xPTR)"},
+	{"%#v", fnValue, "(fmt_test.Fn)(nil)"}, // variable of function type with String method
+	{"%#v", reflect.ValueOf(fnValue), "(fmt_test.Fn)(nil)"},
+	{"%#v", [1]Fn{fnValue}, "[1]fmt_test.Fn{(fmt_test.Fn)(nil)}"}, // array of function type with String method
+	{"%#v", reflect.ValueOf([1]Fn{fnValue}), "[1]fmt_test.Fn{(fmt_test.Fn)(nil)}"},
+	{"%#v", fnValue.String, "(func() string)(0xPTR)"}, // method value from function type
+	{"%#v", reflect.ValueOf(fnValue.String), "(func() string)(0xPTR)"},
+	{"%#v", reflect.ValueOf(fnValue).Method(0), "(func() string)(0xPTR)"},
+	{"%#v", U{}.u, "(func() string)(nil)"}, // unexported function field
+	{"%#v", reflect.ValueOf(U{}.u), "(func() string)(nil)"},
+	{"%#v", reflect.ValueOf(U{}).Field(0), "(func() string)(nil)"},
+	{"%#v", U{fn: fnValue}.fn, "(fmt_test.Fn)(nil)"}, // unexported field of function type with String method
+	{"%#v", reflect.ValueOf(U{fn: fnValue}.fn), "(fmt_test.Fn)(nil)"},
+	{"%#v", reflect.ValueOf(U{fn: fnValue}).Field(1), "(fmt_test.Fn)(nil)"},
+
 	// Whole number floats are printed without decimals. See Issue 27634.
 	{"%#v", 1.0, "1"},
 	{"%#v", 1000000.0, "1e+06"},
@@ -1438,6 +1497,9 @@ var mallocTest = []struct {
 	{0, `Fprintf(buf, "%s")`, func() { mallocBuf.Reset(); Fprintf(&mallocBuf, "%s", "hello") }},
 	{0, `Fprintf(buf, "%x")`, func() { mallocBuf.Reset(); Fprintf(&mallocBuf, "%x", 7) }},
 	{0, `Fprintf(buf, "%x")`, func() { mallocBuf.Reset(); Fprintf(&mallocBuf, "%x", 1<<16) }},
+	{1, `Fprintf(buf, "%x")`, func() { mallocBuf.Reset(); i := 1 << 16; Fprintf(&mallocBuf, "%x", i) }}, // not constant
+	{4, `Fprintf(buf, "%v")`, func() { mallocBuf.Reset(); s := []int{1, 2}; Fprintf(&mallocBuf, "%v", s) }},
+	{1, `Fprintf(buf, "%v")`, func() { mallocBuf.Reset(); type P struct{ x, y int }; Fprintf(&mallocBuf, "%v", P{1, 2}) }},
 	{2, `Fprintf(buf, "%80000s")`, func() { mallocBuf.Reset(); Fprintf(&mallocBuf, "%80000s", "hello") }}, // large buffer (>64KB)
 	// If the interface value doesn't need to allocate, amortized allocation overhead should be zero.
 	{0, `Fprintf(buf, "%x %x %x")`, func() {
@@ -1452,8 +1514,6 @@ func TestCountMallocs(t *testing.T) {
 	switch {
 	case testing.Short():
 		t.Skip("skipping malloc count in short mode")
-	case runtime.GOMAXPROCS(0) > 1:
-		t.Skip("skipping; GOMAXPROCS>1")
 	case race.Enabled:
 		t.Skip("skipping malloc count under race detector")
 	}