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| Original file line number | Diff line number | Diff line change |
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| # Undetected cyclic dependency between module extensions | ||
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| This repository illustrates an issue where Bazel does not detect a cyclic | ||
| dependency between imported module extensions and instead silently disregards | ||
| tags on the affected extension. | ||
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| ## Expected behavior | ||
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| You can observe the expected behavior with the following command: | ||
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| ``` | ||
| $ (cd module_b; bazel fetch @extension_2//:defs.bzl) | ||
| DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_b TAG module_b_tag_1 | ||
| DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_b TAG module_b_tag_2 | ||
| DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_a TAG module_a_tag_1 | ||
| DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_a TAG module_a_tag_2 | ||
| DEBUG: .../module_a~override/extension_2.bzl:5:10: extension_2 found hello from extension_1, 4 tags | ||
| ``` | ||
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| Note that 4 tags of `extension_1` are reported. | ||
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| ## Faulty behavior | ||
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| You can observe the faulty behavior by changing the extension imports in | ||
| `module_b` as follows: | ||
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| ```diff | ||
| diff --git a/module_b/MODULE.bazel b/module_b/MODULE.bazel | ||
| index 16a8f90..8f57311 100644 | ||
| --- a/module_b/MODULE.bazel | ||
| +++ b/module_b/MODULE.bazel | ||
| @@ -3,15 +3,15 @@ module(name = "module_b") | ||
| bazel_dep(name = "module_a") | ||
| local_path_override(module_name = "module_a", path = "../module_a") | ||
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| -# extension_1 = use_extension("@module_a//:extensions.bzl", "extension_1") | ||
| -# extension_2 = use_extension("@module_a//:extensions.bzl", "extension_2") | ||
| +extension_1 = use_extension("@module_a//:extensions.bzl", "extension_1") | ||
| +extension_2 = use_extension("@module_a//:extensions.bzl", "extension_2") | ||
| # $ (cd module_b; bazel fetch @extension_2//:defs.bzl) | ||
| # DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_a TAG module_a_tag_1 | ||
| # DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_a TAG module_a_tag_2 | ||
| # DEBUG: .../module_a~override/extension_2.bzl:5:10: extension_2 found hello from extension_1, 2 tags | ||
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| -extension_1 = use_extension("@module_a//:extension_1.bzl", "extension_1") | ||
| -extension_2 = use_extension("@module_a//:extension_2.bzl", "extension_2") | ||
| +# extension_1 = use_extension("@module_a//:extension_1.bzl", "extension_1") | ||
| +# extension_2 = use_extension("@module_a//:extension_2.bzl", "extension_2") | ||
| # $ (cd module_b; bazel fetch @extension_2//:defs.bzl) | ||
| # DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_b TAG module_b_tag_1 | ||
| # DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_b TAG module_b_tag_2 | ||
| ``` | ||
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| And then executing the following command: | ||
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| ``` | ||
| $ (cd module_b; bazel fetch @extension_2//:defs.bzl) | ||
| DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_a TAG module_a_tag_1 | ||
| DEBUG: .../module_a~override/extension_1.bzl:7:18: MODULE module_a TAG module_a_tag_2 | ||
| DEBUG: .../module_a~override/extension_2.bzl:5:10: extension_2 found hello from extension_1, 2 tags | ||
| ``` | ||
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| Note that no only 2 tags of `extension_1` are reported. The tags defined in | ||
| `module_b` are lost. | ||
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| ## For reference | ||
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| Bazel does detect the cyclic dependency from the context of `module_a` which | ||
| defines the module extensions `extension_1` and `extension_2`. | ||
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| First modify the imports in `module_a` as follows: | ||
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| ```diff | ||
| diff --git a/module_a/MODULE.bazel b/module_a/MODULE.bazel | ||
| index 5ff4cb7..11259b0 100644 | ||
| --- a/module_a/MODULE.bazel | ||
| +++ b/module_a/MODULE.bazel | ||
| @@ -1,6 +1,6 @@ | ||
| module(name = "module_a") | ||
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| -# extension_1 = use_extension("//:extensions.bzl", "extension_1") | ||
| +extension_1 = use_extension("//:extensions.bzl", "extension_1") | ||
| # ``` | ||
| # $ (cd module_a; bazel fetch @extension_1//:defs.bzl) | ||
| # ERROR: Circular definition of repositories generated by module extensions and/or .bzl files: | ||
| @@ -13,7 +13,7 @@ module(name = "module_a") | ||
| # ERROR: cycles detected during target parsing | ||
| # ``` | ||
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| -extension_1 = use_extension("//:extension_1.bzl", "extension_1") | ||
| +# extension_1 = use_extension("//:extension_1.bzl", "extension_1") | ||
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| extension_1.tag(name = "module_a_tag_1") | ||
| extension_1.tag(name = "module_a_tag_2") | ||
| ``` | ||
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| Then execute the following command to trigger the error: | ||
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| ``` | ||
| $ (cd module_a; bazel fetch @extension_1//:defs.bzl) | ||
| ERROR: Circular definition of repositories generated by module extensions and/or .bzl files: | ||
| .-> @_main~extension_1~extension_1 | ||
| | extension 'extension_1' defined in //:extensions.bzl | ||
| | //:extensions.bzl | ||
| | //:extension_2.bzl | ||
| | @_main~extension_1~extension_1//:defs.bzl | ||
| `-- @_main~extension_1~extension_1 | ||
| ERROR: cycles detected during target parsing | ||
| ``` |