RFC: Add an AGENTS.md in c/image

image/AGENTS.md

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+# Commitments
+
+go.podman.io/image/v5 (aka c/image) promises to keep a stable Go API,
+following the general Go semantic versioning rules, and not bumping
+the major version. Keep that promise.
+
+# Prioritize human attention
+
+Avoid repetitive code. As a rule of thumb, 3 repetitions of
+the same >5-line pattern should probably be refactored, _if_
+a clear abstraction can be found.
+
+Human’s screens (and attention spans) are limited. Avoid very long
+linear functions, look for ways to abstract / split the function
+_if_ the resulting smaller functions have a clear purpose and interface.
+Use blank lines within function bodies sparingly, less than
+you would do by default (but do use them when separating large conceptually
+different parts of the function’s code).
+
+Don't add redundant comments that add no value. Code in style
+    // Add a user
+    ….addUser(…)
+is _never_ acceptable.
+
+# Tests
+
+The default pattern is TestFunctionName, or TestObjectMethodName
+(in that case, with no underscore), containing all tests for a function/method.
+Do not _default_ to adding a new test function when adding a feature
+to an existing function.
+
+Tests should typically be table-driven. When choosing between a
+semantically precise table types and short table entries, prefer short table entries
+so that the whole test table easily fits on a screen. For example, usually don't
+add .name fields to test tables - have such descriptions as comments on the same line
+as the other test content.
+
+It should be very rare to test error message text. Just a test that an error is reported
+is frequently enough.
+
+# Existing code
+
+Have some (but not slavish) deference to existing code structure: don't
+refactor a whole file just to add 3 lines, if that addition would be otherwise clean.
+
+If some refactoring _is_ beneficial, the goal is to have one or more _pure_
+refactoring commits (which don't change the observable behavior at all, and document that
+in the commit message), followed by a separate commit that adds the required feature.
+
+# Documentation
+
+Most data structures with scope larger than a single function probably need documentation.
+Document field interactions:
+    UseTLS bool
+    TLSConfig … // Only used if UseTLS
+special values:
+    Name // "" if unknown
+_Never_ add comments that add no value:
+    // A user
+    type User struct { …}
+or
+    Name // name
+is never acceptable.
+
+Most functions should have documentation, documenting in enough detail that, when working
+on a caller code, humans can read only the callee’s documentation without reading the callee
+itself — but no more! The documentation of a function should almost never contain _how_
+the function does it, the caller shouldn’t need to care.
+
+If such a function documentation looks too convoluted, that’s a sign that the function’s interface
+is probably not right — the function boundary is in the wrong place, or an abstraction is missing
+to simplify the concepts.
+
+Comments within function bodies should typically only document non-obvious implementation
+decisions, non-obvious constraints that require using one approach over another, or _sometimes_
+delineate significantly conceptually separate parts of the same function (definitely not
+after every blank line). It should not generally be necessary to document, in a caller, what calling another
+function does — if that is confusing, the callee should probably be renamed or refactored.