compiler: disambiguate function-local named types (#5336)

* compiler: make getTypeCodeName a method on compilerContext

* testdata: add regression tests for function-local named types

* compiler: disambiguate function-local named types

* Some PR feedback

compiler/compiler.go

@@ -92,6 +92,7 @@ type compilerContext struct {
 	pkg              *types.Package
 	packageDir       string // directory for this package
 	runtimePkg       *types.Package
+	localTypeNames   typeutil.Map // *types.Named (synthetic local from generic instantiation) -> string
 }
 
 // newCompilerContext returns a new compiler context ready for use, most
@@ -313,6 +314,11 @@ func CompilePackage(moduleName string, pkg *loader.Package, ssaPkg *ssa.Package,
 	// Convert AST to SSA.
 	ssaPkg.Build()
 
+	// Assign names to function-local named types before compiling the
+	// package, so that types declared in different functions (or in
+	// different instantiations of a generic function) do not collide.
+	c.scanLocalTypes(ssaPkg)
+
 	// Initialize debug information.
 	if c.Debug {
 		c.cu = c.dibuilder.CreateCompileUnit(llvm.DICompileUnit{