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Found via fuzz testing:
fuzz: elapsed: 0s, gathering baseline coverage: 0/4 completed
fuzz: elapsed: 0s, gathering baseline coverage: 4/4 completed, now fuzzing with 4 workers
fuzz: elapsed: 1s, execs: 1955 (1385/sec), new interesting: 6 (total: 10)
--- FAIL: FuzzTemplatefile (1.41s)
--- FAIL: FuzzTemplatefile (0.00s)
testing.go:1825: panic: not a string
goroutine 1245 [running]:
runtime/debug.Stack()
/opt/hostedtoolcache/go/1.25.9/x64/src/runtime/debug/stack.go:26 +0x9b
testing.tRunner.func1()
/opt/hostedtoolcache/go/1.25.9/x64/src/testing/testing.go:1825 +0x1d0
panic({0x9ed640?, 0xb16cb0?})
/opt/hostedtoolcache/go/1.25.9/x64/src/runtime/panic.go:783 +0x132
github.com/zclconf/go-cty/cty.Value.AsString({{{0xb1be40?, 0xebf8e0?}}, {0x0?, 0x0?}})
/home/runner/go/pkg/mod/github.com/zclconf/go-cty@v1.18.1/cty/value_ops.go:1458 +0x218
github.com/TypedSoftware/templatefile.templatefile({0xc0053aebd0, 0x23}, {0xc0053aec30, 0x2d}, {0xc0052c7c50, 0x4})
/home/runner/work/templatefile/templatefile/templatefile.go:141 +0x391d
github.com/TypedSoftware/templatefile.FuzzTemplatefile.func1(0xc005399880, {0xc004decd59, 0x6}, {0xc0052c7c50, 0x4})
/home/runner/work/templatefile/templatefile/templatefile_test.go:51 +0x146
reflect.Value.call({0x9fb9c0?, 0xa99598?, 0x13?}, {0xa6bf86, 0x4}, {0xc0053cf6e0, 0x3, 0x4?})
/opt/hostedtoolcache/go/1.25.9/x64/src/reflect/value.go:581 +0xcc6
reflect.Value.Call({0x9fb9c0?, 0xa99598?, 0xd8a540?}, {0xc0053cf6e0?, 0xa6b300?, 0xd21ae0?})
/opt/hostedtoolcache/go/1.25.9/x64/src/reflect/value.go:365 +0xb9
testing.(*F).Fuzz.func1.1(0xc005399880?)
/opt/hostedtoolcache/go/1.25.9/x64/src/testing/fuzz.go:341 +0x32a
testing.tRunner(0xc005399880, 0xc0053e0090)
/opt/hostedtoolcache/go/1.25.9/x64/src/testing/testing.go:1934 +0xea
created by testing.(*F).Fuzz.func1 in goroutine 21
/opt/hostedtoolcache/go/1.25.9/x64/src/testing/fuzz.go:328 +0x637
Failing input written to testdata/fuzz/FuzzTemplatefile/a3034cdd38718cd7
To re-run:
go test -run=FuzzTemplatefile/a3034cdd38718cd7
I've added the seed corpus as well.
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This PR adds a basic fuzzing setup which has already identified some error handling improvements!
The new workflow will run 10s of fuzzing and upload any seed corpus that fails as an artifact.
See also: Tutorial: Getting started with fuzzing, a great intro. I don't expect this to catch much over the long term, but it's free!