Re-vendor and re-patch grisu (#597)

* Let's have a maintenance/ folder

And move the existing maintenance notes

* Pull grisu3.{h,c} from upstream

* Patch the header file

* Patch the c file

* Use #pragma once

* Document this process

* Remove the working copies

Author: jennybc

.Rbuildignore

@@ -49,3 +49,4 @@
 ^[.]?air[.]toml$
 ^scratch\.R$
 ^compile_commands\.json$
+^maintenance$

MAINTENANCE.md maintenance/README.mdMAINTENANCE.md renamed to maintenance/README.md

@@ -0,0 +1,66 @@
+# Vendoring grisu3 from MathGeoLib
+
+The `grisu3.c` and `grisu3.h` files in `src/` are vendored from the [MathGeoLib](https://github.com/juj/MathGeoLib) library. We maintain local modifications documented as patch files.
+
+## Files in maintenance/
+
+- **`grisu3-pull-from-upstream.R`**: Script to download fresh grisu3 files from upstream
+- **`grisu3-upstream-info.txt`**: Records the upstream commit SHA and date
+- **`patches/grisu3-header.patch`**: Modifications to `grisu3.h`
+- **`patches/grisu3-source.patch`**: Modifications to `grisu3.c`
+
+## Workflow to re-vendor grisu3
+
+```r
+# 1. Pull fresh upstream files to maintenance/
+source("maintenance/01_pull-grisu3-upstream.R")
+```
+
+This downloads `grisu3.{c,h}` from upstream to the `maintenance/` directory.
+
+```bash
+# 2. Apply patches and copy to src/
+cd maintenance
+patch < patches/grisu3-header.patch
+patch < patches/grisu3-source.patch
+cp grisu3.h ../src/grisu3.h
+cp grisu3.c ../src/grisu3.c
+cd ..
+```
+
+## What we modify
+
+The patches transform the upstream grisu3 code for vroom's needs:
+
+**Header simplifications** (`grisu3-header.patch`):
+- Add Jukka Jylänki copyright header
+- Remove MathGeoLib-specific includes (`#include "../MathBuildConfig.h"`)
+- Remove Emscripten support
+- Remove unused function declarations (`f32_to_string`, `u32_to_string`, `i32_to_string`, hex functions)
+- Simplify C++ string support (remove conditional compilation)
+
+**Source modifications** (`grisu3-source.patch`):
+- Add copyright headers (Jukka Jylänki and mikkelfj)
+- Use `snprintf()` instead of `sprintf()` for buffer safety
+- Remove unused helper functions (`u32_to_string`, `i32_to_string`, `f32_to_string`, hex functions)
+- Add simplified `i_to_str()` function for internal use
+- Include mikkelfj modifications for better decimal formatting:
+  - Handle whole numbers as integers (< 10^15)
+  - Fix zero prefix (.1 => 0.1) for JSON export
+  - Prefer unscientific notation for short decimals
+  - These modifications have been here ever since grisu3.c first appeared in vroom, so Jim Hester must have found them somewhere.
+- Remove `#include "grisu3.h"` (not needed in vroom's structure)
+
+## Why vendor grisu3?
+
+vroom uses grisu3 for fast, accurate double-to-string conversion when writing CSV files (see `src/vroom_write.cc:208`). The vendored version is simpler than the full MathGeoLib implementation—we only keep what vroom needs: the `dtoa_grisu3()` function.
+
+## Upstream source
+
+**Repository**: https://github.com/juj/MathGeoLib
+**Path**: `src/Math/grisu3.{c,h}`
+**Current version**: See `grisu3-upstream-info.txt` for the specific commit SHA
+
+The original grisu3 algorithm is from the research paper:
+> "Printing Floating-Point Numbers Quickly And Accurately with Integers"
+> by Florian Loitsch

maintenance/grisu3-README.md

@@ -0,0 +1,59 @@
+# Pull grisu3 files from upstream MathGeoLib repository
+# https://github.com/juj/MathGeoLib
+#
+# After running this script, apply patches from maintenance/patches/
+# to get the versions vroom actually uses. See 02_apply-grisu3-patches.txt
+
+library(usethis)
+library(gh)
+
+# Upstream: https://github.com/juj/MathGeoLib/tree/master/src/Math
+owner <- "juj"
+repo <- "MathGeoLib"
+repo_spec <- paste0(owner, "/", repo)
+
+# Get current HEAD SHA
+gh_result <- gh(
+  "/repos/{owner}/{repo}/commits/{ref}",
+  owner = owner,
+  repo = repo,
+  ref = "HEAD"
+)
+upstream_sha <- gh_result$sha
+upstream_date <- as.Date(gh_result$commit$author$date)
+
+message(sprintf(
+  "Upstream SHA: %s (%s)",
+  substr(upstream_sha, 1, 7),
+  upstream_date
+))
+# Upstream SHA: 55053da (2023-01-21)
+
+# Download grisu3 files to maintenance/ for patching
+use_github_file(
+  repo_spec = repo_spec,
+  path = "src/Math/grisu3.h",
+  save_as = "maintenance/grisu3.h",
+  ref = upstream_sha
+)
+
+use_github_file(
+  repo_spec = repo_spec,
+  path = "src/Math/grisu3.c",
+  save_as = "maintenance/grisu3.c",
+  ref = upstream_sha
+)
+
+writeLines(
+  c(
+    sprintf("grisu3 vendored from: https://github.com/%s", repo_spec),
+    sprintf("Commit: %s", upstream_sha),
+    sprintf("Date: %s", upstream_date),
+    sprintf(
+      "Permalink: https://github.com/%s/tree/%s/src/Math",
+      repo_spec,
+      upstream_sha
+    )
+  ),
+  "maintenance/grisu3-upstream-info.txt"
+)

maintenance/grisu3-pull-from-upstream.R

@@ -0,0 +1,4 @@
+grisu3 vendored from: https://github.com/juj/MathGeoLib
+Commit: 55053da5e3e55a83043af7324944407b174c3724
+Date: 2023-01-21
+Permalink: https://github.com/juj/MathGeoLib/tree/55053da5e3e55a83043af7324944407b174c3724/src/Math

maintenance/grisu3-upstream-info.txt

@@ -0,0 +1,90 @@
+--- grisu3.h
++++ grisu3.h
+@@ -1,3 +1,14 @@
++/* Copyright Jukka Jylänki
++   Licensed under the Apache License, Version 2.0 (the "License");
++   you may not use this file except in compliance with the License.
++   You may obtain a copy of the License at
++       http://www.apache.org/licenses/LICENSE-2.0
++   Unless required by applicable law or agreed to in writing, software
++   distributed under the License is distributed on an "AS IS" BASIS,
++   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
++   See the License for the specific language governing permissions and
++   limitations under the License. */
++
+ /* This file is part of an implementation of the "grisu3" double to string
+ 	conversion algorithm described in the research paper
+ 
+@@ -6,18 +17,9 @@
+ 	http://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf */
+ #pragma once
+ 
+-#include "../MathBuildConfig.h"
++extern "C"
++{
+ 
+-#include <stdint.h>
+-
+-#ifdef __cplusplus
+-extern "C" {
+-#endif
+-
+-#ifdef __EMSCRIPTEN__
+-int js_double_to_string(double d, char *dst);
+-#endif
+-
+ /// Converts the given double-precision floating point number to a string representation.
+ /** For most inputs, this string representation is the
+ 	shortest such, which deserialized again, returns the same bit
+@@ -30,50 +32,12 @@
+ 	@return the number of characters written to dst, excluding the null terminator (which
+ 		is always written) is returned here. */
+ int dtoa_grisu3(double v, char *dst);
+-#define f64_to_string dtoa_grisu3
+ 
+-int f32_to_string(float v, char *dst);
+-
+-/// Converts an unsigned 32-bit integer to a string. Longest 32-bit unsigned integer is
+-/// 4294967295, which is 10 bytes (11 if including \0)
+-/** @param val The number to convert.
+-	@param dst [out] The unsigned number will be written here
+-		as a null-terminated string. The conversion algorithm will write at most 11 bytes
+-		to this buffer. (null terminator is included in this count).
+-		The dst pointer may not be null.
+-	@return the number of characters written to dst, excluding the null terminator (which
+-		is always written) is returned here. */
+-int u32_to_string(uint32_t val, char *dst);
+-
+-/// Similar to u32_to_string(), but prints the number in hexadecimal, inluding leading "0x".
+-int u32_to_hex_string(uint32_t val, char *str);
+-
+-/// Converts an signed 32-bit integer to a string. Longest 32-bit signed integer is
+-/// -2147483648, which is 11 bytes (12 if including \0)
+-/** @param val The number to convert.
+-	@param dst [out] The unsigned number will be written here
+-		as a null-terminated string. The conversion algorithm will write at most 12 bytes
+-		to this buffer. (null terminator is included in this count).
+-		The dst pointer may not be null.
+-	@return the number of characters written to dst, excluding the null terminator (which
+-		is always written) is returned here. */
+-int i32_to_string(int i, char *dst);
+-
+-/// Similar to i32_to_string(), but prints the number in signed hexadecimal, inluding leading "0x".
+-int i32_to_hex_string(int i, char *str);
+-
+-#ifdef __cplusplus
+ }
+-#endif
+ 
+ #ifdef __cplusplus
+ 
+-#if defined(MATH_ENABLE_STL_SUPPORT)
+ #include <string>
+-#endif
++std::string dtoa_grisu3_string(double v);
+ 
+-#if defined(MATH_ENABLE_STL_SUPPORT) || defined(MATH_CONTAINERLIB_SUPPORT)
+-StringT dtoa_grisu3_string(double v);
+ #endif
+-
+-#endif