Serialize saved sessions more efficiently #1496
Description
:CopilotChatSave currently stores all the data as JSON; here's an example:
Click to expand
$ cat /Users/victor.alvarez/.local/share/nvim/copilotchat_history/go.json | jq [4:30:27 PM]
[
{
"content": "##neovim://selection\nWhat's the point of calling `Grow()`? I may as well be managing the internal byte slice myself.",
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"content": "The point of calling `Grow()` on `strings.Builder` is to optimize memory allocation. By preallocating enough space for the final string, you avoid multiple reallocations as you append each substring. This improves performance, especially when concatenating many strings.\nManaging the internal byte slice yourself would require you to handle allocation, resizing, and conversion to a string manually. `strings.Builder` abstracts these details and ensures safe, efficient string construction. Using `Grow()` with `Builder` gives you control over allocation without sacrificing safety or convenience.",
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"content": "Can you specifically explain what `strings.Builder` takes care of for me?",
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"content": "`strings.Builder` handles several things for you:\n1. **Efficient memory management:** It automatically grows its internal buffer as needed, minimizing allocations.\n2. **Safe string construction:** It prevents accidental misuse, such as reading from the buffer before writing, or using it after calling `String()`.\n3. **Type safety:** It provides methods like `WriteString`, `WriteByte`, and `WriteRune` for appending different types.\n4. **Conversion:** It efficiently converts the buffer to a string with `String()` without unnecessary copying.\n5. **No manual slice management:** You don’t need to manage capacity, resizing, or conversion from `[]byte` to `string` yourself.\n\nIn summary, `strings.Builder` abstracts away manual buffer management, making string concatenation safer and more efficient.",
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"content": "Is the internal buffer an array or a slice?",
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"content": "The internal buffer of `strings.Builder` is a slice of bytes (`[]byte`). This allows dynamic resizing as data is appended.",
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{
"content": "##neovim://selection\nCan you give an example of the first bullet point?",
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"content": "Certainly! The first bullet point refers to using a value receiver when the receiver is a slice that doesn't need to be mutated.\n**Example:**\n```go\ntype IntSlice []int\n\n// Value receiver: does not mutate the slice\nfunc (s IntSlice) Sum() int {\n total := 0\n for _, v := range s {\n total += v\n }\n return total\n}\n```\nHere, `Sum()` uses a value receiver because it only reads from the slice and does not modify it. This is efficient and idiomatic in Go.",
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"content": "Does this copy the backing array? I think no.",
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"content": "Correct, it does not copy the backing array. \nWhen you pass a slice as a value receiver, Go copies the slice header (pointer, length, capacity), but both the original and the copy point to the same backing array. \nOnly the slice descriptor is copied, not the underlying data.",
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{
"content": "##neovim://selection\nWhy is this a convention? What's so unclear about having both pointer and value receivers?",
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"content": "Mixing pointer and value receivers in the same type can be unclear because:\n1. **Method set confusion:** \n Value receivers can be called on both values and pointers, but pointer receivers can only be called on pointers. This affects which methods are available depending on how you use the type.\n\n2. **Mutability ambiguity:** \n Pointer receivers can modify the receiver; value receivers cannot. Mixing them makes it harder to reason about which methods change state and which do not.\n\n3. **Consistency:** \n Using one style consistently makes code easier to read and maintain. Mixing styles can lead to subtle bugs, especially if you accidentally use a value when you meant to use a pointer.\n\nIn short, it's a convention because consistency reduces confusion and potential errors, especially for people reading or maintaining the code.",
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"content": "So is the rule that if you have a type, either all methods should have pointer receivers or all methods should have value receivers?",
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"content": "The rule is: **For a given type, use either all pointer receivers or all value receivers for its methods, unless you have a clear, justified reason to mix them.**\n- Use **pointer receivers** if methods modify the receiver or if the type is large.\n- Use **value receivers** if the type is small and methods don’t modify the receiver.\n\nMixing is discouraged because it can lead to confusion and subtle bugs, but it’s allowed if there’s a good reason. Consistency is preferred.",
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"content": "Give an example where this is enforced and one where it's not enforced.",
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"content": "**Enforced (consistent pointer receivers):**\n```go\ntype Counter struct {\n Count int\n}\n\nfunc (c *Counter) Increment() {\n c.Count++\n}\n\nfunc (c *Counter) Reset() {\n c.Count = 0\n}\n```\nAll methods use pointer receivers, so you always call them on a pointer (`&Counter{}`).\n---\n**Not enforced (mixed receivers):**\n```go\ntype Counter struct {\n Count int\n}\n\nfunc (c Counter) Value() int {\n return c.Count\n}\n\nfunc (c *Counter) Increment() {\n c.Count++\n}\n```\nHere, `Value()` uses a value receiver, while `Increment()` uses a pointer receiver. This can be confusing, as the method set differs depending on whether you have a value or a pointer, and it’s less clear which methods mutate the receiver.",
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"content": "Wouldn't it be more common for a type to have methods that mutate as well as don't mutate it?",
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"content": "Yes, it's common for a type to have both mutating and non-mutating methods. \nIn such cases, Go convention is to use **pointer receivers for all methods**, even for those that don't mutate the receiver. \nThis maintains consistency, avoids confusion with the method set, and ensures that all methods are available regardless of whether you have a pointer or a value.",
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"content": "What if a type evolves, and you initially had only non-mutating methods but later added mutating ones? Would you have to change all the existing methods to use pointer receivers? What happens to clients?",
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"content": "If a type evolves from only non-mutating methods (value receivers) to include mutating methods (pointer receivers), it’s best practice to change all methods to use pointer receivers for consistency.\n**What happens to clients?**\n- Existing code that called non-mutating methods on values will need to use pointers instead (e.g., change `obj.Method()` to `(&obj).Method()`).\n- This can be a breaking change, requiring updates in client code.\n- If you don’t update the non-mutating methods to pointer receivers, the method set will be inconsistent, which can lead to confusion and subtle bugs.\n\n**Summary:** \nFor consistency and maintainability, update all methods to use pointer receivers. This may require client code changes, but it avoids future confusion and errors.",
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"content": "Give me an example where receivers are mixed, and I can only call some methods on pointers and some on values.",
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"content": "Certainly! Here’s an example:\n```go\ntype Counter struct {\n Count int\n}\n\n// Value receiver: can be called on both values and pointers\nfunc (c Counter) Value() int {\n return c.Count\n}\n\n// Pointer receiver: can only be called on pointers\nfunc (c *Counter) Increment() {\n c.Count++\n}\n```\n**Usage:**\n```go\nvar c Counter\n\nc.Value() // OK: value receiver\nc.Increment() // ERROR: cannot call pointer receiver on value\n\n(&c).Increment() // OK: pointer receiver\n(&c).Value() // OK: value receiver\n```\n**Explanation:** \n- `Value()` can be called on both `c` and `&c`.\n- `Increment()` can only be called on `&c`.\n- If you try `c.Increment()`, Go will give an error: \n `cannot call pointer method Increment on Counter`\n\nThis demonstrates how mixing receivers can restrict which methods are available depending on whether you have a value or a pointer.",
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"content": "The compiler doesn't give me an error for c.Increment(). It automatically takes the address of c for me. So isn't this a non-issue?",
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"content": "You're correct—Go automatically takes the address of a value to call pointer receiver methods when possible. \nSo, `c.Increment()` works even though `Increment` has a pointer receiver, and the compiler implicitly converts it to `(&c).Increment()`.\n**However:**\n- This only works for addressable values (variables, not temporary values or literals).\n- Mixing receivers can still cause confusion about mutability and method sets.\n- For non-addressable values (e.g., `Counter{}.Increment()`), you’ll get a compile error.\n\n**Summary:** \nWhile Go helps by auto-addressing, consistency in receiver types is still recommended for clarity and to avoid subtle issues, especially with non-addressable values.",
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]
Suggestion: use something like protocol buffers for compact, fast, and language-agnostic serialization / deserialization. There are a couple of Lua libraries which we may be able to use here (1, 2).