gopls/internal/analysis/yield: improve diagnostic

This change adds the location of the second (reached) yield call
to the diagnostic in the form of RelatedInformation.

Also, for both the primary and related positions, it now
reports the start and end range of the enclosing yield CallExpr,
instead of the single point of the SSA Call instruction, which
is just the CallExpr.Lparen.  (We should aim always to report
meaningful ranges, not just points.)

Tested interactively, since analysistest doesn't yet have a means
of testing related information, nor do we generally assert column
information; but see golang/go#75800.

Change-Id: I70d54375c33ef3c85ce6dd7b53803b9f961e42dc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/712360
Reviewed-by: Markus Kusano <kusano@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>

Author: adonovan

gopls/internal/analysis/yield/yield.go

@@ -31,6 +31,7 @@ import (
 	"golang.org/x/tools/go/ssa"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/internal/analysisinternal"
+	"golang.org/x/tools/internal/moreiters"
 )
 
 //go:embed doc.go
@@ -121,14 +122,45 @@ func run(pass *analysis.Pass) (any, error) {
 					for _, instr := range b.Instrs[start:] {
 						switch instr := instr.(type) {
 						case *ssa.Call:
+
+							// Precondition: v has a pos within a CallExpr.
+							enclosingCall := func(v ssa.Value) ast.Node {
+								pos := v.Pos()
+								cur, ok := inspector.Root().FindByPos(pos, pos)
+								if !ok {
+									panic(fmt.Sprintf("can't find node at %v", safetoken.StartPosition(pass.Fset, pos)))
+								}
+								call, ok := moreiters.First(cur.Enclosing((*ast.CallExpr)(nil)))
+								if !ok {
+									panic(fmt.Sprintf("no call enclosing %v", safetoken.StartPosition(pass.Fset, pos)))
+								}
+								return call.Node()
+							}
+
 							if !info.reported && ssaYieldCalls[instr] != nil {
 								info.reported = true
-								where := "" // "" => same yield call (a loop)
+								var (
+									where   = "" // "" => same yield call (a loop)
+									related []analysis.RelatedInformation
+								)
+								// Also report location of reached yield call, if distinct.
 								if instr != call {
 									otherLine := safetoken.StartPosition(pass.Fset, instr.Pos()).Line
 									where = fmt.Sprintf("(on L%d) ", otherLine)
+									otherCallExpr := enclosingCall(instr)
+									related = []analysis.RelatedInformation{{
+										Pos:     otherCallExpr.Pos(),
+										End:     otherCallExpr.End(),
+										Message: "other call here",
+									}}
 								}
-								pass.Reportf(call.Pos(), "yield may be called again %safter returning false", where)
+								callExpr := enclosingCall(call)
+								pass.Report(analysis.Diagnostic{
+									Pos:     callExpr.Pos(),
+									End:     callExpr.End(),
+									Message: fmt.Sprintf("yield may be called again %safter returning false", where),
+									Related: related,
+								})
 							}
 						case *ssa.If:
 							// Visit both successors, unless cond is yield() or its negation.