cmd/cgo: improve error messages

api/next/51945.txt

@@ -0,0 +1 @@
+pkg errors, func AsType[$0 error](error) ($0, bool) #51945

api/next/68021.txt

@@ -0,0 +1,13 @@
+pkg go/ast, func ParseDirective(token.Pos, string) (Directive, bool) #68021
+pkg go/ast, method (*Directive) End() token.Pos #68021
+pkg go/ast, method (*Directive) ParseArgs() ([]DirectiveArg, error) #68021
+pkg go/ast, method (*Directive) Pos() token.Pos #68021
+pkg go/ast, type Directive struct #68021
+pkg go/ast, type Directive struct, Args string #68021
+pkg go/ast, type Directive struct, ArgsPos token.Pos #68021
+pkg go/ast, type Directive struct, Name string #68021
+pkg go/ast, type Directive struct, Slash token.Pos #68021
+pkg go/ast, type Directive struct, Tool string #68021
+pkg go/ast, type DirectiveArg struct #68021
+pkg go/ast, type DirectiveArg struct, Arg string #68021
+pkg go/ast, type DirectiveArg struct, Pos token.Pos #68021

api/next/71287.txt

@@ -0,0 +1,4 @@
+pkg testing, method (*B) ArtifactDir() string #71287
+pkg testing, method (*F) ArtifactDir() string #71287
+pkg testing, method (*T) ArtifactDir() string #71287
+pkg testing, type TB interface, ArtifactDir() string #71287

api/next/73161.txt

@@ -0,0 +1 @@
+pkg net/http/httputil, type ReverseProxy struct, Director //deprecated #73161

doc/go_spec.html

@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Language version go1.25 (Feb 25, 2025)",
+	"Subtitle": "Language version go1.26 (Oct 1, 2025)",
 	"Path": "/ref/spec"
 }-->
 
@@ -3173,7 +3173,7 @@ <h3 id="Composite_literals">Composite literals</h3>
 
 <p>
 Unless the LiteralType is a type parameter,
-its <a href="#Underlying_types">underlying type
+its <a href="#Underlying_types">underlying type</a>
 must be a struct, array, slice, or map type
 (the syntax enforces this constraint except when the type is given
 as a TypeName).
@@ -4873,7 +4873,7 @@ <h4 id="Operator_precedence">Operator precedence</h4>
 x &lt;= f()                   // x &lt;= f()
 ^a &gt;&gt; b                    // (^a) >> b
 f() || g()                 // f() || g()
-x == y+1 &amp;&amp; &lt;-chanInt &gt; 0  // (x == (y+1)) && ((<-chanInt) > 0)
+x == y+1 &amp;&amp; &lt;-chanInt &gt; 0  // (x == (y+1)) && ((&lt;-chanInt) > 0)
 </pre>
 
 
@@ -6635,7 +6635,7 @@ <h4 id="For_clause">For statements with <code>for</code> clause</h4>
 
 <pre>
 var prints []func()
-for i := 0; i < 5; i++ {
+for i := 0; i &lt; 5; i++ {
 	prints = append(prints, func() { println(i) })
 	i++
 }
@@ -6772,7 +6772,7 @@ <h4 id="For_range">For statements with <code>range</code> clause</h4>
 variable, which must be of integer type.
 Otherwise, if the iteration variable is declared by the "range" clause or is absent,
 the type of the iteration values is the <a href="#Constants">default type</a> for <code>n</code>.
-If <code>n</code> &lt= 0, the loop does not run any iterations.
+If <code>n</code> &lt;= 0, the loop does not run any iterations.
 </li>
 
 <li>
@@ -7799,7 +7799,7 @@ <h3 id="Min_and_max">Min and max</h3>
 </p>
 
 <pre>
-min(x, y)    == if x <= y then x else y
+min(x, y)    == if x &lt;= y then x else y
 min(x, y, z) == min(min(x, y), z)
 </pre>
 

doc/godebug.md

@@ -153,6 +153,16 @@ for example,
 see the [runtime documentation](/pkg/runtime#hdr-Environment_Variables)
 and the [go command documentation](/cmd/go#hdr-Build_and_test_caching).
 
+### Go 1.26
+
+Go 1.26 added a new `httpcookiemaxnum` setting that controls the maximum number
+of cookies that net/http will accept when parsing HTTP headers. If the number of
+cookie in a header exceeds the number set in `httpcookiemaxnum`, cookie parsing
+will fail early. The default value is `httpcookiemaxnum=3000`. Setting
+`httpcookiemaxnum=0` will allow the cookie parsing to accept an indefinite
+number of cookies. To avoid denial of service attacks, this setting and default
+was backported to Go 1.25.2 and Go 1.24.8.
+
 ### Go 1.25
 
 Go 1.25 added a new `decoratemappings` setting that controls whether the Go

doc/next/3-tools.md

@@ -7,5 +7,15 @@
 a replacement for `go tool doc`: it takes the same flags and arguments and
 has the same behavior.
 
+<!-- go.dev/issue/75432 -->
+The `go fix` command, following the pattern of `go vet` in Go 1.10,
+now uses the Go analysis framework (`golang.org/x/tools/go/analysis`).
+This means the same analyzers that provide diagnostics in `go vet`
+can be used to suggest and apply fixes in `go fix`.
+The `go fix` command's historical fixers, all of which were obsolete,
+have been removed and replaced by a suite of new analyzers that
+offer fixes to use newer features of the language and library.
+<!-- I'll write a blog post that discusses this at length. --adonovan -->
+
 ### Cgo {#cgo}
 

doc/next/6-stdlib/99-minor/errors/51945.md

@@ -0,0 +1,2 @@
+The new [AsType] function is a generic version of [As]. It is type-safe, faster,
+and, in most cases, easier to use.

doc/next/6-stdlib/99-minor/go/ast/68021.md

@@ -0,0 +1,4 @@
+The new [ParseDirective] function parses [directive
+comments](/doc/comment#Syntax), which are comments such as `//go:generate`.
+Source code tools can support their own directive comments and this new API
+should help them implement the conventional syntax.

doc/next/6-stdlib/99-minor/net/http/httputil/73161.md

@@ -0,0 +1,11 @@
+The [ReverseProxy.Director] configuration field is deprecated
+in favor of [ReverseProxy.Rewrite].
+
+A malicious client can remove headers added by a `Director` function
+by designating those headers as hop-by-hop. Since there is no way to address
+this problem within the scope of the `Director` API, we added a new
+`Rewrite` hook in Go 1.20. `Rewrite` hooks are provided with both the
+unmodified inbound request received by the proxy and the outbound request
+which will be sent by the proxy.
+
+Since the `Director` hook is fundamentally unsafe, we are now deprecating it.

doc/next/6-stdlib/99-minor/testing/71287.md

@@ -0,0 +1,18 @@
+The new methods [T.ArtifactDir], [B.ArtifactDir], and [F.ArtifactDir]
+return a directory in which to write test output files (artifacts).
+
+When the `-artifacts` flag is provided to `go test`,
+this directory will be located under the output directory
+(specified with `-outputdir`, or the current directory by default).
+Otherwise, artifacts are stored in a temporary directory
+which is removed after the test completes.
+
+The first call to `ArtifactDir` when `-artifacts` is provided
+writes the location of the directory to the test log.
+
+For example, in a test named `TestArtifacts`,
+`t.ArtifactDir()` emits:
+
+```
+=== ARTIFACTS Test /path/to/artifact/dir
+```

src/archive/tar/common.go

@@ -39,6 +39,7 @@ var (
 	errMissData        = errors.New("archive/tar: sparse file references non-existent data")
 	errUnrefData       = errors.New("archive/tar: sparse file contains unreferenced data")
 	errWriteHole       = errors.New("archive/tar: write non-NUL byte in sparse hole")
+	errSparseTooLong   = errors.New("archive/tar: sparse map too long")
 )
 
 type headerError []string

src/archive/tar/reader.go

@@ -531,12 +531,17 @@ func readGNUSparseMap1x0(r io.Reader) (sparseDatas, error) {
 		cntNewline int64
 		buf        bytes.Buffer
 		blk        block
+		totalSize  int
 	)
 
 	// feedTokens copies data in blocks from r into buf until there are
 	// at least cnt newlines in buf. It will not read more blocks than needed.
 	feedTokens := func(n int64) error {
 		for cntNewline < n {
+			totalSize += len(blk)
+			if totalSize > maxSpecialFileSize {
+				return errSparseTooLong
+			}
 			if _, err := mustReadFull(r, blk[:]); err != nil {
 				return err
 			}
@@ -569,8 +574,8 @@ func readGNUSparseMap1x0(r io.Reader) (sparseDatas, error) {
 	}
 
 	// Parse for all member entries.
-	// numEntries is trusted after this since a potential attacker must have
-	// committed resources proportional to what this library used.
+	// numEntries is trusted after this since feedTokens limits the number of
+	// tokens based on maxSpecialFileSize.
 	if err := feedTokens(2 * numEntries); err != nil {
 		return nil, err
 	}

src/archive/tar/reader_test.go

@@ -621,6 +621,11 @@ func TestReader(t *testing.T) {
 			},
 			Format: FormatPAX,
 		}},
+	}, {
+		// Small compressed file that uncompresses to
+		// a file with a very large GNU 1.0 sparse map.
+		file: "testdata/gnu-sparse-many-zeros.tar.bz2",
+		err:  errSparseTooLong,
 	}}
 
 	for _, v := range vectors {

src/archive/zip/reader_test.go

@@ -1213,7 +1213,6 @@ func TestFS(t *testing.T) {
 			[]string{"a/b/c"},
 		},
 	} {
-		test := test
 		t.Run(test.file, func(t *testing.T) {
 			t.Parallel()
 			z, err := OpenReader(test.file)
@@ -1247,7 +1246,6 @@ func TestFSWalk(t *testing.T) {
 			wantErr: true,
 		},
 	} {
-		test := test
 		t.Run(test.file, func(t *testing.T) {
 			t.Parallel()
 			z, err := OpenReader(test.file)

src/cmd/asm/internal/arch/arm64.go

@@ -195,149 +195,6 @@ func ARM64RegisterShift(reg, op, count int16) (int64, error) {
 	return int64(reg&31)<<16 | int64(op)<<22 | int64(uint16(count)), nil
 }
 
-// ARM64RegisterExtension constructs an ARM64 register with extension or arrangement.
-func ARM64RegisterExtension(a *obj.Addr, ext string, reg, num int16, isAmount, isIndex bool) error {
-	Rnum := (reg & 31) + int16(num<<5)
-	if isAmount {
-		if num < 0 || num > 7 {
-			return errors.New("index shift amount is out of range")
-		}
-	}
-	if reg <= arm64.REG_R31 && reg >= arm64.REG_R0 {
-		if !isAmount {
-			return errors.New("invalid register extension")
-		}
-		switch ext {
-		case "UXTB":
-			if a.Type == obj.TYPE_MEM {
-				return errors.New("invalid shift for the register offset addressing mode")
-			}
-			a.Reg = arm64.REG_UXTB + Rnum
-		case "UXTH":
-			if a.Type == obj.TYPE_MEM {
-				return errors.New("invalid shift for the register offset addressing mode")
-			}
-			a.Reg = arm64.REG_UXTH + Rnum
-		case "UXTW":
-			// effective address of memory is a base register value and an offset register value.
-			if a.Type == obj.TYPE_MEM {
-				a.Index = arm64.REG_UXTW + Rnum
-			} else {
-				a.Reg = arm64.REG_UXTW + Rnum
-			}
-		case "UXTX":
-			if a.Type == obj.TYPE_MEM {
-				return errors.New("invalid shift for the register offset addressing mode")
-			}
-			a.Reg = arm64.REG_UXTX + Rnum
-		case "SXTB":
-			if a.Type == obj.TYPE_MEM {
-				return errors.New("invalid shift for the register offset addressing mode")
-			}
-			a.Reg = arm64.REG_SXTB + Rnum
-		case "SXTH":
-			if a.Type == obj.TYPE_MEM {
-				return errors.New("invalid shift for the register offset addressing mode")
-			}
-			a.Reg = arm64.REG_SXTH + Rnum
-		case "SXTW":
-			if a.Type == obj.TYPE_MEM {
-				a.Index = arm64.REG_SXTW + Rnum
-			} else {
-				a.Reg = arm64.REG_SXTW + Rnum
-			}
-		case "SXTX":
-			if a.Type == obj.TYPE_MEM {
-				a.Index = arm64.REG_SXTX + Rnum
-			} else {
-				a.Reg = arm64.REG_SXTX + Rnum
-			}
-		case "LSL":
-			a.Index = arm64.REG_LSL + Rnum
-		default:
-			return errors.New("unsupported general register extension type: " + ext)
-
-		}
-	} else if reg <= arm64.REG_V31 && reg >= arm64.REG_V0 {
-		switch ext {
-		case "B8":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_8B & 15) << 5)
-		case "B16":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_16B & 15) << 5)
-		case "H4":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_4H & 15) << 5)
-		case "H8":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_8H & 15) << 5)
-		case "S2":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_2S & 15) << 5)
-		case "S4":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_4S & 15) << 5)
-		case "D1":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_1D & 15) << 5)
-		case "D2":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_2D & 15) << 5)
-		case "Q1":
-			if isIndex {
-				return errors.New("invalid register extension")
-			}
-			a.Reg = arm64.REG_ARNG + (reg & 31) + ((arm64.ARNG_1Q & 15) << 5)
-		case "B":
-			if !isIndex {
-				return nil
-			}
-			a.Reg = arm64.REG_ELEM + (reg & 31) + ((arm64.ARNG_B & 15) << 5)
-			a.Index = num
-		case "H":
-			if !isIndex {
-				return nil
-			}
-			a.Reg = arm64.REG_ELEM + (reg & 31) + ((arm64.ARNG_H & 15) << 5)
-			a.Index = num
-		case "S":
-			if !isIndex {
-				return nil
-			}
-			a.Reg = arm64.REG_ELEM + (reg & 31) + ((arm64.ARNG_S & 15) << 5)
-			a.Index = num
-		case "D":
-			if !isIndex {
-				return nil
-			}
-			a.Reg = arm64.REG_ELEM + (reg & 31) + ((arm64.ARNG_D & 15) << 5)
-			a.Index = num
-		default:
-			return errors.New("unsupported simd register extension type: " + ext)
-		}
-	} else {
-		return errors.New("invalid register and extension combination")
-	}
-	return nil
-}
-
 // ARM64RegisterArrangement constructs an ARM64 vector register arrangement.
 func ARM64RegisterArrangement(reg int16, name, arng string) (int64, error) {
 	var curQ, curSize uint16

src/cmd/asm/internal/asm/asm.go

@@ -248,7 +248,7 @@ func (p *Parser) asmData(operands [][]lex.Token) {
 	case obj.TYPE_CONST:
 		switch sz {
 		case 1, 2, 4, 8:
-			nameAddr.Sym.WriteInt(p.ctxt, nameAddr.Offset, int(sz), valueAddr.Offset)
+			nameAddr.Sym.WriteInt(p.ctxt, nameAddr.Offset, sz, valueAddr.Offset)
 		default:
 			p.errorf("bad int size for DATA argument: %d", sz)
 		}
@@ -262,10 +262,10 @@ func (p *Parser) asmData(operands [][]lex.Token) {
 			p.errorf("bad float size for DATA argument: %d", sz)
 		}
 	case obj.TYPE_SCONST:
-		nameAddr.Sym.WriteString(p.ctxt, nameAddr.Offset, int(sz), valueAddr.Val.(string))
+		nameAddr.Sym.WriteString(p.ctxt, nameAddr.Offset, sz, valueAddr.Val.(string))
 	case obj.TYPE_ADDR:
 		if sz == p.arch.PtrSize {
-			nameAddr.Sym.WriteAddr(p.ctxt, nameAddr.Offset, int(sz), valueAddr.Sym, valueAddr.Offset)
+			nameAddr.Sym.WriteAddr(p.ctxt, nameAddr.Offset, sz, valueAddr.Sym, valueAddr.Offset)
 		} else {
 			p.errorf("bad addr size for DATA argument: %d", sz)
 		}

src/cmd/asm/internal/asm/parse.go

@@ -775,7 +775,7 @@ func (p *Parser) registerExtension(a *obj.Addr, name string, prefix rune) {
 
 	switch p.arch.Family {
 	case sys.ARM64:
-		err := arch.ARM64RegisterExtension(a, ext, reg, num, isAmount, isIndex)
+		err := arm64.ARM64RegisterExtension(a, ext, reg, num, isAmount, isIndex)
 		if err != nil {
 			p.errorf("%v", err)
 		}