struct: return error instead of panic when MapTo receives a nil pointer (fixes #369)#383
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nghiack7 wants to merge 2 commits into
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struct: return error instead of panic when MapTo receives a nil pointer (fixes #369)#383nghiack7 wants to merge 2 commits into
nghiack7 wants to merge 2 commits into
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May 9, 2026 14:54
Calling MapTo (or Section.MapTo) with a nil struct pointer caused a panic in mapToField because val.Elem() on a nil pointer returns a zero reflect.Value, and the subsequent val.Type() call on that zero value triggers a runtime panic. Add an IsValid check after the Pointer dereference and return a descriptive error, matching the expected behaviour of the method (returns error) instead of crashing the caller. Fixes go-ini#369
…ter structs - Change single if to for loop so chained/double pointers are fully dereferenced - Auto-initialize nil pointers via reflect.New instead of returning an error - Fixes go-ini#369 (nil pointer panic on MapTo) and go-ini#370 (slice of *Struct panic) Previously mapToField would panic when encountering a nil pointer inside a slice of struct pointers ([]*Peer pattern common in WireGuard-style configs). The fix mirrors encoding/json behavior: walk the pointer chain, allocating any nil links, then map into the concrete value.
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Problem
Two related bugs in
mapToFieldwhen the target is a nil pointer or a slice of struct pointers:MapTopanics when the destination struct field is a nil pointer (e.g.var s *S; f.MapTo(&s))MapTopanics when mapping into a[]*Structfield (slice of struct pointers), common in WireGuard-style INI configs with repeated[Peer]sectionsBoth root causes are the same:
mapToFieldonly unwrapped one level of pointer indirection and never initialized nil pointers.Fix
Replace the single
if val.Kind() == reflect.Pointerblock with aforloop that:**T,***T, etc.)reflect.New(mirrorsencoding/jsonbehavior)Tests
Test_MapToNilPointer— regression for panic: nil struct pointer to MapTo #369; verifies nil pointer is auto-initialized and fields are populatedTest_MapToSliceOfStructPointers— regression for panic: slice of struct pointers #370; verifies[]*PeerwithAllowNonUniqueSectionsmaps correctlyFixes #369, fixes #370