cmd/go: clarify that -coverpkg uses import paths

This change amends the long-form help output for 'go help build' and
'go help testflag' to specify that the '-coverpkg' flag operates
explicitly on import paths as well as package names. Import paths are
fundamental for precise specification of packages versus unqualified
package names, and the naming of the flag '-coverpkg' and its original
documentation leads a user to assume that it only operates on the
simple, unqualified package name form. The situation warrants
clarification.

Fixes #69653

Author: matttproud

src/cmd/go/internal/test/test.go

@@ -235,10 +235,10 @@ control the execution of any test:
 	    Sets -cover.
 
 	-coverpkg pattern1,pattern2,pattern3
-	    Apply coverage analysis in each test to packages matching the patterns.
-	    The default is for each test to analyze only the package being tested.
-	    See 'go help packages' for a description of package patterns.
-	    Sets -cover.
+	    Apply coverage analysis in each test to packages and import paths
+	    matching the patterns. The default is for each test to analyze only the
+	    package being tested. See 'go help packages' for a description of
+	    package patterns. Sets -cover.
 
 	-cpu 1,2,4
 	    Specify a list of GOMAXPROCS values for which the tests, benchmarks or

src/cmd/go/internal/work/build.go

@@ -104,10 +104,10 @@ and test commands:
 		Sets -cover.
 	-coverpkg pattern1,pattern2,pattern3
 		For a build that targets package 'main' (e.g. building a Go
-		executable), apply coverage analysis to each package matching
-		the patterns. The default is to apply coverage analysis to
+		executable), apply coverage analysis to each package and import path
+		matching the patterns. The default is to apply coverage analysis to
 		packages in the main Go module. See 'go help packages' for a
-		description of package patterns.  Sets -cover.
+		description of package patterns. Sets -cover.
 	-v
 		print the names of packages as they are compiled.
 	-work