transform: add debug info in interface lowering pass

This is fake debug info. It doesn't point to a source location because
there is no source location. However, it helps to correctly attribute
code size usage to particular packages.

I've also updated builder/sizes.go with some debugging helpers.

builder/sizes.go

@@ -17,6 +17,9 @@ import (
 	"github.com/tinygo-org/tinygo/goenv"
 )
 
+// Set to true to print extra debug logs.
+const sizesDebug = false
+
 // programSize contains size statistics per package of a compiled program.
 type programSize struct {
 	Packages map[string]packageSize
@@ -514,6 +517,9 @@ func readSection(section memorySection, addresses []addressLine, addSize func(st
 			// There is a gap: there is a space between the current and the
 			// previous line entry.
 			addSize("(unknown)", line.Address-addr, false)
+			if sizesDebug {
+				fmt.Printf("%08x..%08x %4d: unknown (gap)\n", addr, line.Address, line.Address-addr)
+			}
 		}
 		if addr > line.Address+line.Length {
 			// The current line is already covered by a previous line entry.
@@ -536,6 +542,9 @@ func readSection(section memorySection, addresses []addressLine, addSize func(st
 	if addr < sectionEnd {
 		// There is a gap at the end of the section.
 		addSize("(unknown)", sectionEnd-addr, false)
+		if sizesDebug {
+			fmt.Printf("%08x..%08x %4d: unknown (end)\n", addr, sectionEnd, sectionEnd-addr)
+		}
 	}
 }
 
@@ -556,6 +565,20 @@ func findPackagePath(path string, packagePathMap map[string]string) string {
 		} else if reflectDataRegexp.MatchString(path) {
 			// Parse symbol names like reflect.structTypesSidetable.
 			packagePath = "Go reflect data"
+		} else if path == "<Go interface assert>" {
+			// Interface type assert, generated by the interface lowering pass.
+			packagePath = "Go interface assert"
+		} else if path == "<Go interface method>" {
+			// Interface method wrapper (switch over all concrete types),
+			// generated by the interface lowering pass.
+			packagePath = "Go interface method"
+		} else if path == "<stdin>" {
+			// This can happen when the source code (in Go) doesn't have a
+			// source file and uses "-" as the location. Somewhere this is
+			// converted to "<stdin>".
+			// Convert this back to the "-" string. Eventually, this should be
+			// fixed in the compiler.
+			packagePath = "-"
 		} else {
 			// This is some other path. Not sure what it is, so just emit its directory.
 			packagePath = filepath.Dir(path) // fallback