fix(wasm): correct several bugs in `realloc` by WillLillis · Pull Request #5261 · tree-sitter/tree-sitter

WillLillis · 2026-01-26T06:32:22Z

free memory if 0 size is passed in
Don't memcpy contents if new pointer is NULL
Copy old region's contents only up to size of new region
free old region
also exit early from calloc if call to malloc fails

Supersedes #5234 with more minimal changes and test coverage for the bug.

CC @trim21 I wasn't able to get beancount-format to build locally to give this change a try on your original repro from #5205. If you get a chance to try it out let me know!

Closes malloc for rust wasm32 target is buggy #5205

trim21 · 2026-01-26T06:36:27Z

what's the error when you try to build it?

there is a cargo registry patch in master branch, you can replace it and remove the rust malloc workaround and try.

https://github.com/trim21/beancount-format/tree/master/patches/tree-sitter-language-0.1.6

also I guess there are some bug when region_end == next is true, I forget what I found and why I change it in the original PR.

trim21 · 2026-01-26T06:37:20Z

since you create a new PR I'll close my #5234 .

trim21 · 2026-01-26T06:41:17Z

also while we are fixing malloc, there is also a bug in calloc, if doesn't handle NULL from malloc:

tree-sitter/crates/language/wasm/src/stdlib.c

Lines 110 to 114 in 8816d44

    
           void *calloc(size_t count, size_t size) { 
        
             void *result = malloc(count * size); 
        
             memset(result, 0, count * size); 
        
             return result; 
        
           }

WillLillis · 2026-01-26T06:54:04Z

what's the error when you try to build it?

❯ cargo build -p dprint-plugin-beancount --target wasm32-unknown-unknown --features wasm --release
    Updating crates.io index
error: failed to select a version for `tree-sitter`.
    ... required by package `tree-sitter-beancount v2.4.2 (https://github.com/trim21/tree-sitter-beancount?branch=wasm#110e43d6)`
    ... which satisfies git dependency `tree-sitter-beancount` (locked to 2.4.2) of package `beancount-formatter v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter)`
    ... which satisfies path dependency `beancount-formatter` (locked to 0.1.0) of package `beancount-formatter-cli v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter-cli)`
versions that meet the requirements `~0.26.3` are: 0.26.3

package `tree-sitter` links to the native library `tree-sitter`, but it conflicts with a previous package which links to `tree-sitter` as well:
package `tree-sitter v0.27.0 (/home/lillis/projects/tree-sitter/lib)`
    ... which satisfies path dependency `tree-sitter` of package `beancount-formatter v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter)`
    ... which satisfies path dependency `beancount-formatter` (locked to 0.1.0) of package `beancount-formatter-cli v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter-cli)`
Only one package in the dependency graph may specify the same links value. This helps ensure that only one copy of a native library is linked in the final binary. Try to adjust your dependencies so that only one package uses the `links = "tree-sitter"` value. For more information, see https://doc.rust-lang.org/cargo/reference/resolver.html#links.

failed to select a version for `tree-sitter` which could resolve this conflict

This is with the following changes to the broken-malloc branch to point to my local checkout of tree-sitter with these changes:

diff --git a/crates/beancount-formatter/Cargo.toml b/crates/beancount-formatter/Cargo.toml
index 17113f6..8e2f654 100644
--- a/crates/beancount-formatter/Cargo.toml
+++ b/crates/beancount-formatter/Cargo.toml
@@ -16,7 +16,8 @@ wasm = ["tree-sitter-beancount/wasm"]
 [dependencies]
 tree-sitter-beancount = { git = "https://github.com/trim21/tree-sitter-beancount", branch = "wasm", default-features = false }
 # tree-sitter-beancount = { path = "C:/Users/trim21/projects/tree-sitter-beancount/", default-features = false }
-tree-sitter = { version = "0.26.3" }
+# tree-sitter = { version = "0.26.3" }
+tree-sitter = { path = "../../../tree-sitter/lib" }
 anyhow.workspace = true
 serde.workspace = true
 ropey = '1.6.1'

trim21 · 2026-01-26T06:56:50Z

what's the error when you try to build it?

❯ cargo build -p dprint-plugin-beancount --target wasm32-unknown-unknown --features wasm --release
    Updating crates.io index
error: failed to select a version for `tree-sitter`.
    ... required by package `tree-sitter-beancount v2.4.2 (https://github.com/trim21/tree-sitter-beancount?branch=wasm#110e43d6)`
    ... which satisfies git dependency `tree-sitter-beancount` (locked to 2.4.2) of package `beancount-formatter v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter)`
    ... which satisfies path dependency `beancount-formatter` (locked to 0.1.0) of package `beancount-formatter-cli v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter-cli)`
versions that meet the requirements `~0.26.3` are: 0.26.3

package `tree-sitter` links to the native library `tree-sitter`, but it conflicts with a previous package which links to `tree-sitter` as well:
package `tree-sitter v0.27.0 (/home/lillis/projects/tree-sitter/lib)`
    ... which satisfies path dependency `tree-sitter` of package `beancount-formatter v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter)`
    ... which satisfies path dependency `beancount-formatter` (locked to 0.1.0) of package `beancount-formatter-cli v0.1.0 (/home/lillis/projects/beancount-format/crates/beancount-formatter-cli)`
Only one package in the dependency graph may specify the same links value. This helps ensure that only one copy of a native library is linked in the final binary. Try to adjust your dependencies so that only one package uses the `links = "tree-sitter"` value. For more information, see https://doc.rust-lang.org/cargo/reference/resolver.html#links.

failed to select a version for `tree-sitter` which could resolve this conflict

This is with the following changes to the broken-malloc branch to point to my local checkout of tree-sitter with these changes:

diff --git a/crates/beancount-formatter/Cargo.toml b/crates/beancount-formatter/Cargo.toml
index 17113f6..8e2f654 100644
--- a/crates/beancount-formatter/Cargo.toml
+++ b/crates/beancount-formatter/Cargo.toml
@@ -16,7 +16,8 @@ wasm = ["tree-sitter-beancount/wasm"]
 [dependencies]
 tree-sitter-beancount = { git = "https://github.com/trim21/tree-sitter-beancount", branch = "wasm", default-features = false }
 # tree-sitter-beancount = { path = "C:/Users/trim21/projects/tree-sitter-beancount/", default-features = false }
-tree-sitter = { version = "0.26.3" }
+# tree-sitter = { version = "0.26.3" }
+tree-sitter = { path = "../../../tree-sitter/lib" }
 anyhow.workspace = true
 serde.workspace = true
 ropey = '1.6.1'

there is a version spec that ~0.26.3 on tree-sitter on the beancount-parser （which is a dependency doesn't exists in this repo) so you can't use master branch of tree-sitter to build it, it's 0.27.0 doesn't match ~0.26.3.

WillLillis · 2026-01-26T06:58:20Z

there is a version spec that ~0.26.3 on tree-sitter on the beancount-parser （which is a dependency doesn't exists in this repo) so you can't use master branch of tree-sitter to build it, it's 0.27.0 doesn't match ~0.26.3.

How were you testing your changes then?

Edit: I see, nevermind.

trim21 · 2026-01-26T06:59:55Z

there is a patch.crates-io on tree-sitter-language so the tree-sitter-language resolve a vendor version inside the project

https://github.com/trim21/beancount-format/blob/0669ac8bd7a99867c73af1168f45d5cb43953567/Cargo.toml#L19-L20

It's a small enough change so I think you can only change content of https://github.com/trim21/beancount-format/blob/master/patches/tree-sitter-language-0.1.6/wasm/src/stdlib.c

and also remove these workaround

https://github.com/trim21/beancount-format/blob/0669ac8bd7a99867c73af1168f45d5cb43953567/crates/dprint-plugin-beancount/src/lib.rs#L164-L165

- free memory if 0 size is passed in - Don't `memcpy` contents if new pointer is `NULL` - Copy old region's contents only up to size of new region - free old region Co-authored-by: trim21 <i@trim21.me>

Co-authored-by: trim21 <i@trim21.me>

WillLillis · 2026-01-27T02:14:09Z

Replaced the contents of stdlib.c with the file from this PR, and removed the rust global allocator workaround. Everything seems to be working for beancount-format, so this should be good to land.

tree-sitter-ci-bot · 2026-01-27T02:14:25Z

Backport failed for release-0.26, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin release-0.26
git worktree add -d .worktree/backport-5261-to-release-0.26 origin/release-0.26
cd .worktree/backport-5261-to-release-0.26
git switch --create backport-5261-to-release-0.26
git cherry-pick -x f9d64425dbea3e286e9092e6f5ccd599e728cbc0 b714e2a7c01e8d5abab526f23e40b77c33babcb4

trim21 · 2026-01-30T19:43:52Z

there is indeed some bug in these code

tree-sitter/crates/language/wasm/src/stdlib.c

Lines 128 to 135 in 4f8983b

    
           Region *region_end = region_after(region, region->size); 
        
           // When reallocating the last allocated region, return 
        
           // the same pointer, and skip copying the data. 
        
           if (region_end == next) { 
        
             next = region; 
        
             return malloc(new_size); 
        
           }

haven't findout why...

WillLillis added wasm ci:backport release-0.26 Backport label labels Jan 26, 2026

WillLillis and others added 2 commits January 26, 2026 02:13

fix(wasm): correct several bugs in realloc

f9d6442

- free memory if 0 size is passed in - Don't `memcpy` contents if new pointer is `NULL` - Copy old region's contents only up to size of new region - free old region Co-authored-by: trim21 <i@trim21.me>

fix(wasm): return early from calloc if malloc fails

b714e2a

Co-authored-by: trim21 <i@trim21.me>

WillLillis force-pushed the wasm_realloc_size branch from ee26b3a to b714e2a Compare January 26, 2026 07:13

clason approved these changes Jan 26, 2026

View reviewed changes

WillLillis merged commit 7ad63a8 into tree-sitter:master Jan 27, 2026
24 of 26 checks passed

WillLillis deleted the wasm_realloc_size branch January 27, 2026 02:14

WillLillis mentioned this pull request Jan 27, 2026

fix(wasm): correct several bugs in realloc #5264

Merged

trim21 mentioned this pull request Jan 30, 2026

fix: wasm32 stdlib realloc on heap end #5274

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fix(wasm): correct several bugs in `realloc`#5261

fix(wasm): correct several bugs in `realloc`#5261
WillLillis merged 2 commits intotree-sitter:masterfrom
WillLillis:wasm_realloc_size

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