add test program

analysis/typecheck/typecheck_test.go

@@ -0,0 +1,15 @@
+package typecheck_test
+
+// TODO: Figure out how to test this analyzer.
+// The golang.org/x/tools/go/analysis/analysistest testing tools set up a
+// "GOPATH-style project" [1], which seems to require vendoring dependencies.
+// This is ok for testing the Go standard library but isn't practical for
+// code with several transitive dependencies, as bigslice has.
+// [1] https://pkg.go.dev/golang.org/x/[email protected]/go/analysis/analysistest?tab=doc
+//
+// Until then, run and see no errors for urls but a type error for wrongarg:
+// 	$ go run github.com/grailbio/bigslice/cmd/slicetypecheck \
+// 		github.com/grailbio/bigslice/cmd/urls \
+// 		github.com/grailbio/bigslice/analysis/typecheck/typechecktest/wrongarg
+//	<snip>/wrongarg.go:22:34: bigslice type error: func "testFunc" argument "argInt" requires int, but got string
+//	exit status 3

analysis/typecheck/typechecktest/wrongarg/wrongarg.go

@@ -0,0 +1,23 @@
+// Tests the static slice typechecker.
+//
+// This is a correctly-typed Go program (even though it's incomplete and thus
+// not runnable, for simplicity). However, its bigslice Func invocation is
+// incorrectly typed, and the static typechecker find that, in this case.
+package main
+
+import (
+	"context"
+
+	"github.com/grailbio/bigslice"
+	"github.com/grailbio/bigslice/exec"
+)
+
+var testFunc = bigslice.Func(func(argInt int, argString string) bigslice.Slice {
+	return nil
+})
+
+func main() {
+	ctx := context.Background()
+	var session *exec.Session
+	_ = session.Must(ctx, testFunc, "i should be an int", "i'm ok")
+}