go/analysis/analysistest: Validate analyzers in Run

The standalone analysis drivers (e.g. {single,multi,unit}checker)
all call Validate immediately within main, but somehow we forgot
to do this within analysistest, leading one user practicing
test-first development to get confused.

This change adds the missing assertion.

Fixes golang/go#59164

Change-Id: I02c316ff1dae0a345e80b488c012707a8d0f93ce
Reviewed-on: https://go-review.googlesource.com/c/tools/+/479737
Reviewed-by: Robert Findley <[email protected]>
Run-TryBot: Alan Donovan <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
gopls-CI: kokoro <[email protected]>

Author: adonovan

go/analysis/analysistest/analysistest.go

@@ -289,6 +289,11 @@ func Run(t Testing, dir string, a *analysis.Analyzer, patterns ...string) []*Res
 		return nil
 	}
 
+	if err := analysis.Validate([]*analysis.Analyzer{a}); err != nil {
+		t.Errorf("Validate: %v", err)
+		return nil
+	}
+
 	results := checker.TestAnalyzer(a, pkgs)
 	for _, result := range results {
 		if result.Err != nil {

go/analysis/internal/checker/checker.go

@@ -75,6 +75,7 @@ func RegisterFlags() {
 // Run loads the packages specified by args using go/packages,
 // then applies the specified analyzers to them.
 // Analysis flags must already have been set.
+// Analyzers must be valid according to [analysis.Validate].
 // It provides most of the logic for the main functions of both the
 // singlechecker and the multi-analysis commands.
 // It returns the appropriate exit code.
@@ -142,16 +143,19 @@ func Run(args []string, analyzers []*analysis.Analyzer) (exitcode int) {
 		// TODO: filter analyzers based on RunDespiteError?
 	}
 
-	// Print the results.
+	// Run the analysis.
 	roots := analyze(initial, analyzers)
 
+	// Apply fixes.
 	if Fix {
 		if err := applyFixes(roots); err != nil {
 			// Fail when applying fixes failed.
 			log.Print(err)
 			return 1
 		}
 	}
+
+	// Print the results.
 	return printDiagnostics(roots)
 }
 
@@ -211,8 +215,9 @@ func loadingError(initial []*packages.Package) error {
 	return err
 }
 
-// TestAnalyzer applies an analysis to a set of packages (and their
+// TestAnalyzer applies an analyzer to a set of packages (and their
 // dependencies if necessary) and returns the results.
+// The analyzer must be valid according to [analysis.Validate].
 //
 // Facts about pkg are returned in a map keyed by object; package facts
 // have a nil key.