x/tools/gopls: crash due to missing type in inline.escape

[adonovan]

#!stacks
"sigpanic" && "inline.escape.func1:+27"

Issue created by stacks.

This stack PHhF6w was reported by telemetry:

	case *ast.SelectorExpr:
			// We assume TypeOf returns non-nil.
			if _, ok := info.TypeOf(e.X).Underlying().(*types.Struct); ok {  <---- panic
				lvalue(e.X, escapes) // &s.f on struct
			}

The question here is why is this panic not recovered? The stack is truncated so we can't tell whether inline.Inline was called on behalf of golang.inlineCall golang.inlineAllCalls, or gofix.(*analyzer) inlineCall. However, the first two conditionally call recover if there was a type error in the caller or callee packages, and the third doesn't run on ill-typed code. So either there is a bug in the type checker that causes it to fail to record a type, or more likely, the recover condition is too strict: perhaps the type error is in a transitive dependency. The fix in that case is to compute a "transitively error-free" predicate over packages and call recover if it is false. FWIW, the deprecated go/loader had this feature; perhaps go/packages should too (though it can be derived).

• crash/crash
• runtime.gopanic:+69,+0x153
• runtime.panicmem:=262,+0x2ff
• runtime.sigpanic:+19,+0x2cc
• golang.org/x/tools/internal/refactor/inline.escape.func1:+27,+0xb4
• golang.org/x/tools/internal/refactor/inline.escape.func2:+4,+0xbb
• go/ast.inspector.Visit:+1,+0x37
• go/ast.Walk:+1,+0x43
• go/ast.Walk:+102,+0x2427
• go/ast.walkList[...]:=21,+0x205b
• go/ast.Walk:+51,+0x2048
• go/ast.Walk:+102,+0x2427
• go/ast.walkList[...]:=21,+0x205b
• go/ast.Walk:+51,+0x2048
• go/ast.walkList[...]:=21,+0x1b0b
• go/ast.Walk:+161,+0x1abc
• go/ast.walkList[...]:=21,+0x1f47
• go/ast.Walk:+178,+0xc40
• go/ast.Walk:+299,+0x4cf
• go/ast.Inspect:=372,+0x107
• golang.org/x/tools/internal/refactor/inline.escape:+46,+0xa4
• golang.org/x/tools/internal/refactor/inline.(*state).inlineCall:+40,+0x2df
• golang.org/x/tools/internal/refactor/inline.(*state).inline:+17,+0x1e7

golang.org/x/tools/gopls@v0.19.1 go1.24.4 darwin/arm64 vscode (2)

[gopherbot]

Change https://go.dev/cl/703955 mentions this issue: internal/refactor/inline: fix panic due to nil TypeOf in transitive dependencies

[ANAS727189]

I submitted a fix in https://go-review.googlesource.com/c/tools/+/703955 that adds nil checks in escape and skips analysis for packages with transitive errors.