dotnet-inspect-compatibility

name	dotnet-inspect-compatibility
version	0.1.0
description	Decide whether a change or upgrade is safe — API-surface diffs, behavioral diffs (allocations, exceptions), feature switches, and version resolution.

dotnet-inspect: compatibility and change analysis

Use this skill to decide whether a change is safe to adopt: what changed between two versions and what surface a library exposes. The scenario crosses commands — diff for change, library/package for the surface a single version exposes.

dnx dotnet-inspect -y -- <command>

Did the API surface change?

diff compares a version range from a package, a platform (in-box) library, or two local builds. Pick the lens for the question you are answering:

dnx dotnet-inspect -y -- diff --package System.Text.Json@9.0.0..10.0.0 --breaking
dnx dotnet-inspect -y -- diff --platform System.Runtime@9.0.0..10.0.0 --additive
dnx dotnet-inspect -y -- diff --library old/Foo.dll..new/Foo.dll --changed

--breaking for migration work, --additive for release notes, --changed for in-place member changes, --name-only for a quick list. Narrow with -t TypeName; widen with --all.

Did runtime behavior change? (allocations, exceptions)

-S "Analysis Diff" compares body-level signal deltas between the two versions, not just the API shape. Rows are Member | Signal | Old | New | Delta, where Signal covers allocations, copies, reflection, throws, catches, finallys, unsafe, constructed-exceptions, and optimization shapes. This is how you catch an allocation regression or a change in exception coverage across versions. (For what these signals mean on a single version, see the performance and correctness skills.)

dnx dotnet-inspect -y -- diff --package Foo@1.0.0..2.0.0 -S "Analysis Diff"
dnx dotnet-inspect -y -- diff --library old/Foo.dll..new/Foo.dll -S "Analysis Diff" --changed

Use Analysis Diff for aggregate regression triage. To confirm whether one allocation occurrence was introduced at a caller-selected boundary, resolve one method and request the native Analysis Finding pairs:

dnx dotnet-inspect -y -- diff --package Foo@1.4.0..1.5.0 \
  -t Foo.Parser -m Parse \
  --finding analysis.allocation

PairFinding.Added with Old=absent and New=present confirms allocation onset. Present, Removed, and Changed remain distinct; do not infer onset from an aggregate allocation-count delta.

For a direct-call boundary in one caller method, select the call-site producer:

dnx dotnet-inspect -y -- diff --package Foo@1.4.0..1.5.0 \
  -t Foo.Parser -m Parse \
  --finding analysis.call-site

Rows identify the callees. PairFinding.Added confirms a new direct-call occurrence; Changed reports retained-call facet changes such as moving into a loop.

For a definite unsafe-operation boundary in one method, select the unsafety producer:

dnx dotnet-inspect -y -- diff --package Foo@1.4.0..1.5.0 \
  -t Foo.Parser -m Parse \
  --finding analysis.unsafety

Rows identify unsafe operation kinds and details. PairFinding.Added confirms introduction; Present and Removed distinguish persistence from disappearance without treating endpoint-local IL offsets as identity.

Did the implementation change? (decompiled C# + IL + PDB Source)

-S "Implementation Diff" selects Research-composed body evidence instead of the default API compatibility view. Rows identify the member, producer (C#, IL, or PDB Source), change kind, and producer-owned evidence. C# is decompiled text; PDB Source is Portable-PDB-selected, checksum-verified text acquired locally or through SourceLink. The lanes are peers: PDB-source absence or failure stays visible and never replaces the C# lane. Narrow with -t and -m; use --table, --tsv, or --jsonl for columnar output.

dnx dotnet-inspect -y -- diff --library old/Foo.dll..new/Foo.dll \
  -S "Implementation Diff" --pdb-source --repo /path/to/Foo \
  -t MyType -m HotPath

--repo requires a fully qualified clone path. For raw.githubusercontent.com SourceLink URLs, it reads the committed blob at the SourceLink commit and verifies it against the PDB checksum before fetching the source body remotely. Package or PDB acquisition may still use the network; other SourceLink hosts do not use the local-repository path. Treat these rows as implementation evidence, not semantic-equivalence proof.

What can be configured? (feature switches)

-S Switches on library or package --library reports the behavior and trim/AOT knobs: [FeatureSwitchDefinition]s, runtime host configuration options, and AppContext switches.

dnx dotnet-inspect -y -- library System.Text.Json -S Switches

Which versions to compare

Version resolution is source-scoped. Use Foo --version for the best-known listed version: it reuses each source's matching latest entry and queries sources without one. Use Foo --latest-version to bypass those caches and refresh the newest version across all eligible configured sources, and Foo --versions [N] (add --preview) to list published versions. Unlisted versions are hidden unless --include-unlisted is explicit. --versions-with-feed retains each version/feed pair when source identity matters. Source declaration order is not precedence; load the private-feeds skill for source and credential workflows. Pin with @: Foo@9.0.0, Foo@latest.

For caller-driven onset or bisect work, resolve an inclusive addressable vector, then probe only the cells you choose:

dnx dotnet-inspect -y -- package Foo@1.0.0..2.0.0 --versions
dnx dotnet-inspect -y -- type TargetType --package Foo@1.0.0..2.0.0 --at '#5'
dnx dotnet-inspect -y -- member TargetType TargetMember --package Foo@1.0.0..2.0.0 --at 1.6.0
dnx dotnet-inspect -y -- timeline --package Foo@1.0.0..2.0.0 \
  --type TargetType --members --at first --at last
dnx dotnet-inspect -y -- timeline --package Foo@1.0.0..2.0.0 \
  --type TargetType --member TargetMember \
  --finding analysis.unsafety --at first --at last

--at accepts an exact version, one-based #N, first, or last. Vector resolution does not download every package; only the selected probe is acquired. The agent owns the search policy and bound. For recurrence-safe current onset, walk backward from the bad version until the first successful absence; use binary search only for a predicate known to be monotonic.

timeline renders Evaluations and Transitions over the same vector. Omit --at for a zero-payload address view and midpoint recommendation, repeat --at for sparse probes, or pass --at all for explicit dense traversal. Choose the type-focused census with --type-presence, --members, or --attributes (aliases for api.type, api.member, and api.attribute). Add --member to api.member for one exact member identity track. The same member selector scopes analysis.allocation, analysis.call-site, and analysis.unsafety timelines to one method body. Gap-spanning transitions are evidence across the selected probes, not claims about the exact introduction or removal version.

The range and point probes identify a candidate boundary. Confirm the adjacent pair with Metadata's real Finding comparison rather than inferring introduction from probe text:

dnx dotnet-inspect -y -- diff \
  --package System.Text.Json@8.0.6..9.0.0 \
  -t System.Text.Json.Schema.JsonSchemaExporter \
  -S "Finding Transitions"

An introduction boundary is a row with PairFinding.Added, Old=absent, and New=present. PairFinding.Present means the target exists at both endpoints; for a type target, no row means it exists at neither. Use -m Type.Member:1 for an API member boundary. Use --finding analysis.allocation, --finding analysis.call-site, or --finding analysis.unsafety with exactly one method target for the corresponding Analysis boundary. Use --finding csharp.line or --finding il.op with exactly one method target to inspect native implementation-census transitions. Those lenses preserve complete, absent, and failed outcomes, including added or removed methods.