internal/godoc/internal/doc: support examples on generic methods

Remove bracket contents from generic method example identifiers
to allow them to be paired with examples.

Port of https://go.dev/cl/401761.

Fixes golang/go#52363.

Change-Id: I4404c833d1aa98308407cdc6199fbe6261f256c9
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/401621
Run-TryBot: Jonathan Amsterdam <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Jamal Carvalho <[email protected]>

Author: jba

internal/godoc/internal/doc/example.go

@@ -492,7 +492,7 @@ func classifyExamples(p *Package, examples []*Example) {
 			if !token.IsExported(m.Name) {
 				continue
 			}
-			ids[strings.TrimPrefix(m.Recv, "*")+"_"+m.Name] = &m.Examples
+			ids[strings.TrimPrefix(nameWithoutInst(m.Recv), "*")+"_"+m.Name] = &m.Examples
 		}
 	}
 
@@ -527,6 +527,24 @@ func classifyExamples(p *Package, examples []*Example) {
 	}
 }
 
+// nameWithoutInst returns name if name has no brackets. If name contains
+// brackets, then it returns name with all the contents between (and including)
+// the outermost left and right bracket removed.
+//
+// Adapted from debug/gosym/symtab.go:Sym.nameWithoutInst.
+func nameWithoutInst(name string) string {
+	start := strings.Index(name, "[")
+	if start < 0 {
+		return name
+	}
+	end := strings.LastIndex(name, "]")
+	if end < 0 {
+		// Malformed name, should contain closing bracket too.
+		return name
+	}
+	return name[0:start] + name[end+1:]
+}
+
 // splitExampleName attempts to split example name s at index i,
 // and reports if that produces a valid split. The suffix may be
 // absent. Otherwise, it must start with a lower-case letter and

internal/godoc/internal/doc/example_test.go

@@ -8,13 +8,14 @@ import (
 	"bytes"
 	"fmt"
 	"go/ast"
-	"go/doc"
 	"go/format"
 	"go/parser"
 	"go/token"
 	"reflect"
 	"strings"
 	"testing"
+
+	"golang.org/x/pkgsite/internal/godoc/internal/doc"
 )
 
 const exampleTestFile = `
@@ -616,6 +617,10 @@ type (
 )
 
 func (Conflict) Conflict() {}
+
+type G[T any] int
+
+func (G[T]) M() {}
 `
 	const test = `
 package p_test
@@ -675,6 +680,9 @@ func ExampleConflict_Conflict()        {} // ambiguous with either Conflict or C
 func ExampleConflict_conflict()        {} // ambiguous with either Conflict or Conflict_conflict type
 func ExampleConflict_Conflict_suffix() {} // ambiguous with either Conflict or Conflict_Conflict type
 func ExampleConflict_conflict_suffix() {} // ambiguous with either Conflict or Conflict_conflict type
+
+func ExampleG_M() {}
+func ExampleG_M_suffix() {}
 `
 
 	// Parse literal source code as a *doc.Package.
@@ -724,12 +732,18 @@ func ExampleConflict_conflict_suffix() {} // ambiguous with either Conflict or C
 		// These are implementation dependent due to the ambiguous parsing.
 		"Conflict_Conflict": {"", "suffix"},
 		"Conflict_conflict": {"", "suffix"},
+
+		"G.M": {"", "suffix"},
 	}
 
 	for id := range got {
 		if !reflect.DeepEqual(got[id], want[id]) {
 			t.Errorf("classification mismatch for %q:\ngot  %q\nwant %q", id, got[id], want[id])
 		}
+		delete(want, id)
+	}
+	if len(want) > 0 {
+		t.Errorf("did not find:\n%q", want)
 	}
 }