From 55e2dff4830a24d66126ad229d9e58cd2a003dd3 Mon Sep 17 00:00:00 2001
From: Jacob Quinn <jacob.quinn@cbtravel.com>
Date: Mon, 6 Oct 2025 19:06:25 -0600
Subject: [PATCH] Add check for positive float precision for non-shortest
 float_style

---
 docs/src/writing.md | 2 ++
 src/write.jl        | 7 ++++++-
 test/json.jl        | 7 ++++++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/docs/src/writing.md b/docs/src/writing.md
index 18a980e6..65925fa0 100644
--- a/docs/src/writing.md
+++ b/docs/src/writing.md
@@ -171,6 +171,8 @@ JSON.json(pi_value; float_style=:exp, float_precision=3)
 # [3.142e+00]
 ```
 
+`float_precision` must be a positive integer when `float_style` is `:fixed` or `:exp`.
+
 ### JSON Lines Format
 
 The JSON Lines format is useful for streaming records where each line is a JSON value:
diff --git a/src/write.jl b/src/write.jl
index ef99f052..7a5c9c15 100644
--- a/src/write.jl
+++ b/src/write.jl
@@ -393,6 +393,9 @@ end
 @noinline float_style_throw(fs) = throw(ArgumentError("Invalid float style: $fs"))
 float_style_check(fs) = fs == :shortest || fs == :fixed || fs == :exp || float_style_throw(fs)
 
+@noinline float_precision_throw(fs, fp) = throw(ArgumentError("float_precision must be positive when float_style is $fs; got $fp"))
+float_precision_check(fs, fp) = (fs == :shortest || fp > 0) || float_precision_throw(fs, fp)
+
 # if jsonlines and pretty is not 0 or false, throw an ArgumentError
 @noinline _jsonlines_pretty_throw() = throw(ArgumentError("pretty printing is not supported when writing jsonlines"))
 _jsonlines_pretty_check(jsonlines, pretty) = jsonlines && pretty !== false && !iszero(pretty) && _jsonlines_pretty_throw()
@@ -401,6 +404,7 @@ function json(io::IO, x::T; pretty::Union{Integer,Bool}=false, kw...) where {T}
     opts = WriteOptions(; pretty=pretty === true ? 2 : Int(pretty), kw...)
     _jsonlines_pretty_check(opts.jsonlines, opts.pretty)
     float_style_check(opts.float_style)
+    float_precision_check(opts.float_style, opts.float_precision)
     y = StructUtils.lower(opts.style, x)
     # Use smaller initial buffer size, limited by bufsize
     initial_size = min(sizeguess(y), opts.bufsize)
@@ -423,6 +427,7 @@ function json(x; pretty::Union{Integer,Bool}=false, kw...)
     opts = WriteOptions(; pretty=pretty === true ? 2 : Int(pretty), kw...)
     _jsonlines_pretty_check(opts.jsonlines, opts.pretty)
     float_style_check(opts.float_style)
+    float_precision_check(opts.float_style, opts.float_precision)
     y = StructUtils.lower(opts.style, x)
     buf = stringvec(sizeguess(y))
     pos = json!(buf, 1, y, opts, Any[y], nothing)
@@ -762,4 +767,4 @@ function anyinvalidnumberchars(x)
         end
     end
     return false
-end
\ No newline at end of file
+end
diff --git a/test/json.jl b/test/json.jl
index 47077998..2564ff83 100644
--- a/test/json.jl
+++ b/test/json.jl
@@ -258,6 +258,11 @@ end
     # float_style and float_precision
     @test JSON.json(Float64(π); float_style=:fixed, float_precision=2) == "3.14"
     @test JSON.json(Float64(π); float_style=:exp, float_precision=2) == "3.14e+00"
+    @test_throws ArgumentError JSON.json(Float64(π); float_style=:fixed, float_precision=0)
+    @test_throws ArgumentError JSON.json(Float64(π); float_style=:fixed, float_precision=-1)
+    @test_throws ArgumentError JSON.json(Float64(π); float_style=:exp, float_precision=0)
+    io = IOBuffer()
+    @test_throws ArgumentError JSON.json(io, Float64(π); float_style=:fixed, float_precision=0)
     @test_throws ArgumentError JSON.json(Float64(π); float_style=:not_a_style)
 end
 
@@ -585,4 +590,4 @@ end
     end
 end
 
-end # @testset "JSON.json"
\ No newline at end of file
+end # @testset "JSON.json"